High Strength Microalloyed Magnesium Alloy

The present disclosure is directed to a composite material and method for manufacturing a magnesium composite alloy wherein the magnesium composite alloy has improved thermal and mechanical properties. The improved thermal and mechanical properties are at least in part obtained by the modification of grain boundary properties in the magnesium composite alloy by the addition of nanoscale fillers to the magnesium composite alloy. The magnesium composite alloy has a thermal conductivity that is at least 170 W/m-K, and/or a ductility exceeding 6% elongation to failure (Ef). The magnesium composite alloy is a substituted, quaternary magnesium alloy that exhibits high strength and good processability. The magnesium composite alloy includes additions of calcium, nickel, and/or tin, and such additions have been found to improve the strength and processability of long period stacking order (LPSO) magnesium composite alloys containing one or more rare earth metals (RE) and zinc. It has also been found that the addition of aluminum to the magnesium composite alloy improves the corrosion resistance of the magnesium composite alloy. The addition of calcium, nickel, and/or tin to the magnesium composite alloy can improve the strength of the magnesium composite alloy and/or enhance reduction ratios in the magnesium composite alloy.

BACKGROUND OF THE DISCLOSURE

Magnesium alloys can be used to form a low-density alloy, but such alloys have suffered from poor workability (due to incipient melting, poor ductility, and texture development) as well as poor strength compared to aluminum alloys. Traditional magnesium alloys are primarily strengthened by grain refinement. For example, the AZ series includes a large volume fraction precipitation. However, the precipitates are coarse and there is a low number density of precipitates in the alloy. Also, the precipitation does not follow a sequence which can lead to significant precipitation hardening.

In the last five years, the development of LPSO (long period stacking order) alloys reinforced by fibrous/platelet phases has shown excellent properties with ultimate tensile strengths exceeding 500 MPa and having a high ductility. Most of these alloys are gadolinium-zinc or yttrium-zinc LPSO formers with zirconium or manganese addition for grain refinement, and generally contain 0.5-2 at. % (atomic weight percent) zinc and 2-5 at. % RE. Some of these alloys also include micro-alloying additions. Wrought versions of these alloys are strengthened by plastic deformation where the highly resistant LPSO phase induces dynamic recrystallization during hot forming, thereby resulting in fine grain sizes to create a high strength alloy. However, one issue with this process of forming these alloys is that very high forces are needed to deform these alloys at lower temperatures, thus limiting the ability to produce practical parts from such alloys. Rolling reductions of as little as 5% reduction per pass between anneals have been reported for these LPSO alloys.

Attempts to improve processability while retaining high strength in LPSO alloys have been generally unsuccessful. The high-strength magnesium-RE-based extrusion alloys are categorized into two groups: magnesium-yttrium-zinc-based alloys and magnesium-gadolinium-based alloys. In some cases, gadolinium, yttrium and zinc are added together in order to achieve enhanced strength in the alloy. However, the magnesium-RE-based alloys are typically difficult to extrude, with high RE concentrations necessitating high temperatures and low speed, resulting in a high cost for industrial production.

The addition of soluble alloying elements that create age-hardening alloys in addition to the LPSO phases is a method to increase strength through heat treatments. Processing ability of these alloys can be improved through selection of an alloy composition opening a window of lower flow stress at elevated temperature. An alloy with good processability may likewise not have high elevated temperature strength.

Belgian Pat. No. 654,809 discloses a yttrium-RE-zinc magnesium alloy with up to 10 wt. % yttrium, 3 wt. % RE (other than yttrium), and up to 1.25 wt. % zinc. It is disclosed that at a room temperature (77° F.), the magnesium alloy has poor properties, thus making the magnesium alloy unusable for many applications.

Tikhova (U.S. Pat. No. 4,116,731) discloses a high strength magnesium alloy containing yttrium and neodymium, plus zinc and zirconium. Tikhova teaches that such magnesium alloy is useful for high temperature applications. Tikhova does not teach that such magnesium alloy can be plastically worked and discloses that the magnesium alloy has a tensile yield strength of 18 Kg/mm²(21 ksi).

Inoue Kuwamara Y., Hayashi K., Inoue A., and Masumoto T., “Rapidly solidified powder metallurgy Mg97ZniY2 alloys with excellent tensile yield strength above 600 MPa”, Mater. Trans., 42(7): 1174 (2001), reported >600 MPa strengths in the magnesium-yttrium-zinc system from extruded and heat treated rapidly solidified (partially amorphous) powders.,

Kuwamara (U.S. Pat. No. 8,394,211 and US 2007/0125464) discloses magnesium-yttrium-zinc and magnesium-gadolinium-zinc systems that uses casting, extrusion, and heat-treating processes. Kuwamara teaches such magnesium alloys are castable alloys having high strengths. Kuwamara also discloses gadolinium and other rare earths in the magnesium RE-zinc-zirconium system and the influence of rare earths on mechanical properties such magnesium alloys. Kuwamara discloses that neodymium and cerium resulting in improved properties over yttrium.

Nie, J F, “Precipitation and hardening in magnesium alloys” Metallurgical and Materials Transactions A, 43(11), pp. 3891-3939 (2012), teaches that magnesium alloys can be strengthened by prismatic plates of intrinsically strong precipitate phases.

Zhang, “Recent developments in high-strength Mg-RE-based alloys: Focusing on Mg—Gd and Mg—Y systems,” Journal of Magnesium and Alloys, 6(3), pp. 277-291 (2018), teaches that to develop high-strength magnesium-RE alloys, precipitation strengthening is very crucial.

At present, the microstructure of magnesium-RE-zinc and magnesium-RE-silver systems contain both prismatic and basal plates. The basal plates in such a microstructure have a large aspect ratio (γ″, γ′, basal SFs or 14H LPSO); however, the aspect ratio as well as number density of the prismatic plates (β′, etc.) is much lower that typical precipitates formed in high-strength aluminum alloys.

Zeng teaches that for developing high-strength magnesium-RE alloys, it is equally important to develop the methods and technologies to realize refining grain size of the α-magnesium matrix down to the submicron or even nanometer scale to fulfill the grain refinement strengthening.

Presently, there is still a need for developing magnesium alloys with high UTS both in cast and wrought form. As such, in view of the current state of magnesium alloys, there remains a need for a magnesium alloy that has improved thermal and mechanical properties.

SUMMARY OF THE INVENTION

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the improved mechanical properties of the magnesium composite alloy are optionally at least in part obtained by the addition of long period stacking order phases, and at least partially due to microalloying additions leading to one or more additional precipitates, along with optional solid solution and grain refinement strengthening.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally has 1) a strength exceeding 240 MPa and/or 2) a ductility exceeding 6% elongation to failure (Ef).

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composition alloy is optionally a substituted, quaternary (or quintenary) magnesium alloy that exhibits high strength and good processability, and retains significant mechanical properties to at least 200° C.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes additions of calcium, tin, and/or additional rare earth metals above that required to form the stable LPSO phases, as well as optionally either zirconium or manganese, wherein such additions have been found to improve the strength and processability of long period stacking order (LPSO) magnesium composite alloys containing one or more rare earth metals (RE) and zinc.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes germanium, arsenic, and/or antimony. The addition of germanium, arsenic, and/or antimony to the magnesium composite alloy of amounts of less than 1% can significantly improve the corrosion resistance of the magnesium composite alloy.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes additions of nanoparticles that can be added or substituted for the zirconium or manganese additions for grain refinement and strengthening in the magnesium composite alloy.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes addition of calcium, silver, nickel, copper, and/or tin to improve the strength of the magnesium composite alloy and/or enhance reduction ratios in the magnesium composite alloy.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally is an alloy of magnesium-zinc-RE and the RE includes one or more of cerium, dysprosium, erbium, europium, gadolinium, lanthanum, neodymium, yttrium and/or ytterbium. In one non-limiting embodiment, the RE in the magnesium composite alloy includes one or more gadolinium, yttrium, cerium, and/or neodymium. In another non-limiting specific example, the RE in the magnesium composite alloy includes two or more of gadolinium, yttrium, cerium, and/or neodymium. In another one non-limiting specific example, the RE in the magnesium composite alloy includes yttrium and one or more of gadolinium, cerium, and/or neodymium. In another one non-limiting specific example, the RE in the magnesium composite alloy includes gadolinium and one or more of yttrium, cerium, and/or neodymium. In another one non-limiting specific example, the RE in the magnesium composite alloy includes yttrium and gadolinium. In another specific non-limiting example of this embodiment, the RE constitutes three or more RE wherein one of the RE is yttrium and at least one other RE is gadolinium and/or cerium. In another specific non-limiting example of this embodiment, the RE includes yttrium, gadolinium, and cerium. In another non-limiting embodiment, the magnesium composite alloy includes 0.1-10 wt. % yttrium (and all values and ranges therebetween). In one specific non-limiting example, the magnesium composite alloy includes 0.1-8 wt. % yttrium. In another specific non-limiting example, the magnesium composite alloy includes 0.1-6 wt. % yttrium. In one specific non-limiting example, the magnesium composite alloy includes 0.1-4 wt. % yttrium. In one specific non-limiting example, the magnesium composite alloy includes 0.1-2 wt. % yttrium. In another non-limiting embodiment, the magnesium composite alloy includes 0.1-15 wt. % gadolinium (and all values and ranges therebetween). In one specific non-limiting example, the magnesium composite alloy includes 0.1-12 wt. % gadolinium. In another specific non-limiting example, the magnesium composite alloy includes 0.1-10 wt. % gadolinium. In one specific non-limiting example, the magnesium composite alloy includes 0.1-5 wt. % gadolinium. In one specific non-limiting example, the magnesium composite alloy includes 0.1-3 wt. % gadolinium. In another non-limiting embodiment, the RE in the magnesium composite alloy includes both gadolinium and yttrium. When gadolinium and yttrium are included in the magnesium composite alloy, the weight ratio of gadolinium to yttrium is 0.5:1 to 10:1 (and all values and ranges therebetween). In one specific non-limiting example, the weight ratio of gadolinium to yttrium in the magnesium composite alloy is 0.9:1 to 8:1. In another specific non-limiting example, the weight ratio of gadolinium to yttrium in the magnesium composite alloy is 1:1 to 4:1. In another specific non-limiting example, the weight ratio of gadolinium to yttrium in the magnesium composite alloy is 1:1 to 2:1. In another non-limiting specific example, the weight content of gadolinium is greater than the weight content of yttrium in the magnesium composite alloy. In another non-limiting specific example, the weight ratio of gadolinium to yttrium in the magnesium composite alloy is 5:4 to 3:2. In another non-limiting specific example, the weight ratio of gadolinium to yttrium in the magnesium composite alloy is about 4:3. In another non-limiting specific example, a weight ratio of non-yttrium rare earth metal to yttrium is 1:1 to 20:1 (and all values and ranges therebetween).

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is optionally an alloy of magnesium-zinc-RE and cerium can be optionally included in the magnesium composite alloy. The addition of cerium to the magnesium composite alloy can be a partial or full substitute for gadolinium and/or yttrium in the magnesium composite alloy. In one non-limiting specific example, the weight content of cerium in the magnesium composite alloy, when used, is 0.01-2 wt. % (and all values and ranges therebetween), and typically 0.1-1 wt. %. It has also been found that cerium may optionally be used to replace a portion of the yttrium and/or gadolinium in the magnesium composite alloy without adversely affecting the thermal and mechanical properties of the magnesium composite alloy.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is optionally an alloy of magnesium-zinc-RE and neodymium, dysprosium, and/or erbium can be optionally included in the magnesium composite alloy. The addition of neodymium, dysprosium, and/or erbium to the magnesium composite alloy, when used, can be a partial or full substitute for gadolinium in the magnesium composite alloy. In one non-limiting specific example, the weight content of neodymium, dysprosium, and/or erbium in the magnesium composite alloy is 0.01-4 wt. % (and all values and ranges therebetween), and typically 0.1-2 wt. %.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy can optionally include lanthanum, cerium, europium, and/or ytterbium as microalloying elements to facilitate in the formation of favorable precipitate morphologies in the magnesium composite alloy. In one non-limiting embodiment, the total content of lanthanum, cerium, europium, and/or ytterbium in the magnesium composite alloy, when used, is up to 3 wt. %. In one non-limiting specific example, the total content of lanthanum, cerium, europium, and/or ytterbium in the magnesium composite alloy, when used, is up to 3 wt. %. In another non-limiting specific example, the total content of lanthanum, cerium, europium, and/or ytterbium in the magnesium composite alloy, when used, is 0.01-3 wt. % (and all values and ranges therebetween). In another non-limiting specific example, the total content of lanthanum, cerium, europium, and/or ytterbium in the magnesium composite alloy, when used, is 0.01-1 wt. %.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy that includes RE and optionally zinc. The zinc content in the magnesium composite alloy in an amount of 0.05-7.99 wt. % of the magnesium composite alloy (and all values and ranges therebetween), and typically 0.1-3 wt. % of the magnesium composite alloy. In one non-limiting specific example, zinc is included in the magnesium alloy composite in an amount of 0.1-1.5 wt. % of the magnesium composite alloy. In another non-limiting specific example, the weight content of zinc in the magnesium composite alloy is 0.1-1.25 wt. %. In one non-limiting embodiment, at least a portion of the zinc addition to the magnesium composite alloy is located in the LPSO phase. In another non-limiting embodiment, 0.001-66.67% of the zinc in the magnesium composite alloy can be substituted with nickel and/or copper, and typically 20-66.667% of the zinc in the magnesium composite alloy can be substituted with nickel and/or copper. As such, if the maximum zinc content in the magnesium composite alloy is 3 wt. %, the zinc content in the magnesium composite alloy can optionally be reduced up to 2 wt. % (66.67% reduction from 3 wt. %), and the total weight percent of nickel and/or copper in the magnesium composite alloy can be 0.001-2 wt. %. Likewise, if the maximum zinc content in the magnesium composite alloy is 1.5 wt. %, the zinc content in the magnesium composite alloy can be reduced up to 1 wt. % (66.67% reduction from 1.5 wt. %), and the total weight percent of nickel and/or copper in the magnesium composite alloy can be 0.001-1 wt. %. When nickel and/or copper is optionally partially substituted for zinc in the magnesium composite alloy, nickel and/or copper can be optionally included in the LPSO phase. In another non-limiting embodiment, the nickel content in the magnesium composite alloy, when used, is 0.01-2 wt. % (and all values and ranges therebetween), typically 0.01-1 wt. %, and more typically 0.1-0.8 wt. %. In another non-limiting embodiment, the copper content in the magnesium composite alloy, when used, is 0.01-2 wt. % (and all values and ranges therebetween), typically 0.01-1 wt. %, and more typically 0.1-0.8 wt. %.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy wherein the magnesium composite alloy optionally includes strengthening additives. In one non-limiting embodiment, the magnesium composite alloy includes additions of calcium, nickel, and/or tin. The addition of calcium, nickel, and/or tin to the magnesium composite alloy, when used, can improve the strength of the magnesium composite alloy. For example, the UTS of a magnesium-RE-zinc-zirconium alloy is 38.5 ksi (Alloy A2 in Table 1) whereas a similar alloy containing 2 wt. % nickel is 52.5 ksi (Alloy A5 in Table 1). The A2 alloy has lower gadolinium and yttrium than typical magnesium-gadolinium-yttrium-zinc-zirconium-containing alloys (and a correspondingly lower UTS). However, the trend of increased strength with additional nickel content is expected to hold. Alloy A7 from was successfully rolled, a high RE content alloy, with 10% reduction per pass. The addition of calcium, nickel, and/or tin to the magnesium composite alloy can improve the strength of the magnesium composite alloy and/or the enhanced reduction ratios in alloys of magnesium-RE-zinc that have the optional inclusion of metals such as, but not limited to, zirconium and/or manganese. The inclusion of strengthening additives in the magnesium composite alloy have been found to improve the strength and processability of LPSO magnesium composite alloys containing RE (e.g., cerium, dysprosium, erbium, gadolinium, neodymium, yttrium) and zinc. It has also been found that the addition of aluminum to the magnesium composite alloy improves the corrosion resistance of the magnesium composite alloy. In NaCl-based electrolytes, aluminum containing magnesium-aluminum binary alloys exhibit a corrosion rate of ˜0.5 mg/cm²/day, whereas high RE (gadolinium and yttrium)-containing binaries that include aluminum exhibit a corrosion rate of ˜20 mg/cm²/day. In one non-limiting embodiment, the content of strengthening additives in the magnesium composite alloy, when used, is 0.01-5 wt. % (and all values and ranges therebetween), and typically 0.1-3 wt. %. In one non-limiting specific example, the content of calcium in the magnesium composite alloy, when used, is 0.01-1 wt. % (and all values and ranges therebetween), and typically 0.1-0.8 wt. %. In one non-limiting specific example, the content of tin in the magnesium composite alloy, when used, is 0.01-1 wt. % (and all values and ranges therebetween), and typically 0.1-0.8 wt. %. In one non-limiting specific example, the content of nickel in the magnesium composite alloy, when used, is 0.01-3 wt. % (and all values and ranges therebetween), and typically 0.3-2.0 wt. %.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy wherein the magnesium composite alloy optionally includes additions of zirconium and/or manganese to refine the grain size in the magnesium composite alloy during casting and/or produce dispersoids in the magnesium composite alloy. In one non-limiting embodiment, the total content of zirconium and/or manganese in the magnesium composite alloy is 0.01-1.99 wt. % (and all values and ranges therebetween), and typically 0.2-1.8 wt. %.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy wherein the magnesium composite alloy optionally includes additions of aluminum, calcium, manganese, tin, strontium, and/or zirconium to facilitate in causing additional precipitate to form in the magnesium composite alloy so as to further strengthen the magnesium composite alloy. In one non-limiting embodiment, the total content of aluminum, calcium, manganese, tin, strontium, and/or zirconium in the magnesium composite alloy, when used, is 0.1-5 wt. % (and all values and ranges therebetween). In one specific non-limiting example of this embodiment, the total content of tin, strontium and/or calcium in the magnesium composite alloy is 0.2-4 wt. % (and all values and ranges therebetween). In another specific non-limiting example of this embodiment, the total content of tin, strontium, and/or calcium in the magnesium composite alloy is 0.5-2 wt. %. In another non-limiting specific example, the content of calcium, when used in the magnesium composite alloy, is 0.01-4 wt. % (and all values and ranges therebetween), typically 0.2-2 wt. %, and more typically 0.25-0.5 wt. %. In another non-limiting specific example, the content of tin, when used in the magnesium composite alloy, is 0.01-2 wt. % (and all values and ranges therebetween), typically 0.01-1 wt. %, and more typically 0.25-0.5 wt. %. In another non-limiting specific example, the magnesium composite alloy optionally includes both calcium and tin. It has been found that the addition of tin and calcium to the magnesium composite alloy forms a highly stable magnesium-calcium-tin compound in the magnesium composite alloy that is effective in creating additional precipitate in the magnesium composite alloy.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy wherein the magnesium composite alloy optionally includes additions of indium another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy wherein the magnesium composite alloy optionally includes additions of tin and/or germanium to improve the corrosion resistance of the magnesium composite alloy. In one non-limiting embodiment, the content of tin, when used in the magnesium composite alloy, is 0.01-2 wt. % (and all values and ranges therebetween), typically 0.01-1 wt. %, and more typically 0.25-0.5 wt. %. In another non-limiting embodiment, the content of germanium, when used in the magnesium composite alloy, is 0.01-2 wt. % (and all values and ranges therebetween), typically 0.01-1 wt. %, and more typically 0.25-0.5 wt. %.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy wherein the magnesium composite alloy optionally includes additions of aluminum. The inclusion of aluminum in the magnesium composite alloy is used to improve corrosion resistance of the magnesium composite alloy; however, too much aluminum in the magnesium composite alloy can result in the formation of detrimental MgAl eutectic phases which can greatly inhibit processability of the magnesium composite alloy. In one non-limiting embodiment, the total content of aluminum in the magnesium composite alloy, when used, is 0.01-9.99 wt. % (and all values and ranges therebetween), typically is 0.01-5 wt. %, more typically 0.01-1 wt. %, and even more typically 0.01-0.5 wt. %.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is an alloy of magnesium-zinc-RE and at least 2 wt. % of the RE remains in solid solution in the magnesium phase of the magnesium composite alloy (e.g., hexagonal magnesium phase, etc.) after the processing and heat treatment of the magnesium composite alloy, and wherein the remaining RE and/or RE alloy goes to forming of the LPSO in the magnesium composite alloy and/or as particles of Mg—Re (e.g., Mg3RE and/or Mg2RE) in the magnesium composite alloy.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy includes one or more phases (e.g., LPSO phase, secondary precipitate phase). In one non-limiting embodiment, the magnesium composite alloy includes one or more LPSO phases in the magnesium composite alloy wherein the one or more LPSO phases constitutes 2-60 vol. % (and all values and ranges therebetween) of the magnesium composite alloy, typically 5-55 vol. % of the magnesium composite alloy, more typically 5-40 vol. % of the magnesium composite alloy, and even more typically 5-30 vol. % of the magnesium composite alloy. In another non-limiting embodiment, the magnesium composite alloy includes two or more phases, wherein at least one phase is a LPSO phase, and wherein at least one phase is a secondary phase precipitate that includes a) a magnesium-RE phase (e.g., Mg3RE, Mg2RE, etc.) and/or b) a non-RE precipitate phase (e.g., precipitate that includes one or more of aluminum, calcium, copper, germanium, manganese, nickel, tin, and strontium). The magnesium-RE is a precipitate phase caused by adding more RE to the magnesium composite alloy that can remain in solution in the magnesium composite alloy. Such oversaturation of the magnesium composite alloy with RE results in some of the RE forming a precipitate phase in the magnesium composite alloy. In one non-limiting specific examples, the amount of RE added to the magnesium composite alloy is in excess of 10% of the maximum amount of RE that can stay in solid solution (e.g., RE in solid solution with magnesium composite alloy does not precipitate out of the magnesium composite alloy after being solidified and/or after being heat processed and/or extruded) with the magnesium composite alloy. In another non-limiting specific examples, the amount of RE added to the magnesium composite alloy is in excess of 50% of the maximum amount of RE that can stay in solid solution with the magnesium composite alloy. In another non-limiting specific examples, the amount of RE added to the magnesium composite alloy is in excess of 100% of the maximum amount of RE that can stay in solid solution with the magnesium composite alloy at room temperature (25° C.). In another non-limiting specific examples, the amount of RE added to the magnesium composite alloy is in excess of 10-1000% of the maximum amount of RE (and all values and ranges therebetween) that can stay in solid solution with the magnesium composite alloy. The non-RE precipitate phase is a precipitate phase caused by adding more of a non-RE to the magnesium composite alloy that can remain in solution in the magnesium composite alloy. Such oversaturation of the magnesium composite alloy with the non-RE results in some of the non-RE forming a precipitate phase in the magnesium composite alloy (e.g., magnesium-calcium precipitate, magnesium-manganese precipitate, magnesium-aluminum precipitate, magnesium-zirconium precipitate, magnesium-copper precipitate, magnesium-germanium precipitate, magnesium-nickel precipitate, magnesium-tin precipitate, magnesium-strontium precipitate, etc.). In one non-limiting specific example, the magnesium composite alloy includes at least three phases, wherein at least one phase is a LPSO phase, wherein at least one phase is a magnesium-RE phase, and wherein at least one phase is a non-RE precipitate phase. It has been found that the formation of one or more LPSO phases in the magnesium alloy composite are particularly effective in creating a high strength, corrosion-resistant magnesium composite alloy. In one non-limiting embodiment, the formation of a LPSO phase in the magnesium alloy composite of magnesium-RE-zinc has been found to be particularly effective in creating a high strength, corrosion-resistant magnesium composite alloy. In another non-limiting embodiment, the average size (maximum dimension) of the each of the LPSO phases or plates in the magnesium composite alloy is greater than 2 μm, and typically 2-50 μm (and all values and ranges therebetween), and more typically 5-30 μm. In another non-limiting embodiment, the average size (maximum dimension) of the each of the secondary phase participate in the magnesium composite alloy is generally less than 1 μm.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes both RE and zinc and wherein the weight ratio of RE to zinc is at least 1.2:1. In one non-limiting embodiment, the atomic ratio of RE to zinc is 1.2-40:1 (and all values and ranges therebetween), and typically 1.5-20:1, and more typically 2-4:1. It has been found that such an RE/zinc weight ratio results in a magnesium composite alloy have the desired LPSO phases. In one specific non-limiting example, the weight ration of gadolinium and yttrium to zinc is 1.3-5:1, and typically 2-4:1. Several non-limiting examples of magnesium composite alloy are set forth below:

Example
Mg
Gd
Nd
Y
Zn
Zr
TRE:Zn
TRE:Y

1
98.95
0.75
0.00
0.10
0.05
0.15
17:1
8.5:1

2
99.25
0.50
0.00
0.05
0.05
0.15
11:1
11:1

3
98.80
0.50
0.50
0.00
0.05
0.15
20:1
—

4
99.20
0.50
0.10
0.00
0.05
0.15
12:1
—

5
99.00
0.60
0.10
0.10
0.05
0.15
16:1

8:1

6
95.35
2.00
0.00
1.50
1.00
0.15
3.5:1
2.3:1

7
96.35
1.50
0.00
1.00
1.00
0.15
2.5:1
2.5:1

8
95.85
2.00
1.00
0.00
1.00
0.15
3:1
—

9
96.35
1.00
1.50
0.00
1.00
0.15
2.5:1
—

10
95.85
1.00
1.00
1.00
1.00
0.15
3:1

3:1

Example alloys (in at %)—The rare earth metals in these non-limiting examples are gadolinium, neodymium, and/or yttrium. All ratios are based on at % of the element.

In one non-limiting specific example, for a heat treatable alloy (able to achieve full aMg solutionizing at 500°), the magnesium composite alloy generally has 1) 5:1<TRE:Zn<40:1 (and all values and ranges therebetween) (and all values and ranges therebetween); 2) 0.01 at % <Zn<2 at % (and all values and ranges therebetween), and typically 0.05 at %<Zn<0.20 at %; and 3) if the magnesium composite alloy contains Y, then 6:1<TRE:Y<13:1 (and all values and ranges therebetween). In another non-limiting specific examples, for a magnesium composite alloy having precipitates stable at 500° C., the magnesium composite alloy generally has 1) 2:1<TRE:Zn<4:1 (and all values and ranges therebetween) (and all values and ranges therebetween); 2) 0.01 at %<Zn<2 at % (and all values and ranges therebetween); and 3) if the magnesium composite alloy contains Y, then 1.33:1<TRE:Y<4:1 (and all values and ranges therebetween).

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes at least two additional precipitates, wherein one of the precipitates include at least one RE phase. In one non-limiting embodiment, the at least one rare RE phase includes Mg5-12RE (i.e., 5-12 wt. % RE in magnesium composite alloy).

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes the addition of carbon, carbide, and/or oxide nanoparticles, and wherein the magnesium composite alloy includes 0.01-4.99 wt. % (and all values and ranges therebetween) of such carbon (e.g., graphite, graphene, nano-diamond particles, carbon nanotubes, carbon nano-fibers, etc.), carbide, and/or oxide nanoparticles, and typically includes 0.5-3 wt. % of carbon, carbide, and/or oxide nanoparticles. The addition of carbon, carbide, and/or oxide nanoparticles to the magnesium composite alloy can optionally be used to include the strength of the magnesium composite alloy.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy optionally includes both the α-Mg and LPSO phases have an average dimension of less than 100 mm, typically less than 50 mm, and more typically less than 10 mm. In one non-limiting specific example, the magnesium composite alloy optionally includes both a LPSO phase and an α-Mg phase, wherein both the LPSO phase and the α-Mg phase have an average major dimension of less than 50 microns.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy can be optionally prepared by smelting. The magnesium composite alloy can be formed from one or more elemental metal additions (e.g., magnesium, aluminum, calcium, copper, manganese, neodymium, nickel, RE, tin, strontium, titanium, vanadium, zinc, zirconium, etc.) and/or from one or more master alloy additions (magnesium-aluminum, magnesium-nickel, magnesium-zirconium, magnesium-calcium, magnesium-aluminum-calcium, magnesium-yttrium, magnesium-neodymium, magnesium-cerium, aluminum-RE, nickel-RE, zinc-RE, etc.). The magnesium composite alloy can be formed under a protective gas environment. Non-limiting gas environments include containing SF₆, other protective fluoride environments, and other non-reactive gas environments. During the smelting process, the elemental metal additions and/or master alloy additions are generally added at an elevated temperature which is generally greater that 700° C. Generally, the elemental metal additions and/or master alloy additions are added at a temperature which is no more than 800° C. In one non-limiting arrangement, one or more elemental metal additions and/or master alloy additions are added to molten magnesium and/or a molten magnesium mixture that includes at least 60% magnesium. When one or more elemental metal additions and/or master alloy additions are added to a heated environment and/or to molten magnesium and/or a molten magnesium mixture, the one or more elemental metal additions and/or master alloy additions are generally added under conditions of stirring or motion. In one non-limiting specific arrangement, one or more elemental metal additions and/or master alloy additions are placed in a perforated container that is formed of a material that will not melt at a temperature that is less than 1100° C. (e.g., steel container, etc.), and typically not melt at a temperature that is less than 1200° C., and moving through the perforated container in the molten magnesium and/or a molten magnesium mixture until the one or more elemental metal additions and/or master alloy additions in the perforated container have melted/dissolved in the molten magnesium and/or a molten magnesium mixture. It has been found that adding prealloyed master alloys to the molten magnesium and/or a molten magnesium mixture can improve the yield of RE in the final magnesium composite alloy, and can also inhibit or prevent segregation and settling/slag formation of the rare metals.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy can optionally be direct chill cast or permanent mold cast, and solutionized to homogenize the magnesium composite alloy and to reduce or eliminate eutectic phase formed during solidification of the magnesium cast alloy. In one non-limiting embodiment, the magnesium composite alloy is optionally subjected to a solutionizing process for at least 2 hours (e.g., 2-12 hours, etc.), and typically at least 5 hours (e.g., 5-10 hours, etc.) at a temperature above 480° C. and less than 600° (and all values and ranges therebetween), and typically about 500-540° C. A solutionizing process can be used to reduce or eliminate the amount of precipitant in the magnesium composite alloy that has been formed through eutectic formation. Generally, the solutionizing process can reduce by at least 80%, and typically by at least 90%, the amount of precipitant in the magnesium composite alloy that has been formed through eutectic formation.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy can optionally be aged. In one non-limiting embodiment, the magnesium composite alloy is optionally aged at a temperature of 200-400° C. (and all values and ranges therebetween), and typically 250-320° C. for 2-60 hours (and all values and ranges therebetween), and typically 4-12 hours prior to any optional extrusion of the magnesium composite alloy. Such an optional aging process can result in higher strengths of the magnesium composite alloy. The magnesium composite alloy can be optionally extruded to improve the thermal mechanical properties of the magnesium composite alloy. In another non-limiting embodiment, the magnesium composite alloy is optionally extruded at a temperature of 300-500° C. (and all values and ranges therebetween), and typically 320-420° C. at a rate of 0.1-25 inches/min. (and all values and ranges therebetween), and typically 1-8 inches/min. The magnesium composite alloy can be optionally rolled or forged. In another non-limiting embodiment, the magnesium composite alloy is optionally rolled or forged to create at least a 35% total strain in the magnesium composite alloy, and typically at least a 50% total strain in the magnesium composite alloy. In one non-limiting specific example, a post plastic worked, age hardened treatment of the magnesium composite alloy at a temperature of 250-320° C. for 5-40 hours resulted in a T6 tempered magnesium composite alloy. The magnesium composite alloy can be optionally heat treated. In one non-limiting specific example, the magnesium composite alloy is subject to an annealing precipitation/aging heat treatment for 4-50 hrs. (and all values and ranges therebetween) at a temperature of 200-525° C. (and all values and ranges therebetween).

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy has improved thermal mechanical properties as compared to prior art magnesium alloys, while being more processable than most current magnesium alloy systems. In one non-limiting embodiment, the magnesium composite alloy has a tensile yield strength of at least 120 MPa (17.4 ksi), an ultimate tensile strength (UTS) of at least 200 MPa (29 ksi), and/or an Ef of at least 2%. In one non-limiting specific example, the magnesium composite alloy has a tensile yield strength (YS) of 130-450 Mpa (18.85-62.7 ksi) (and all values and ranges therebetween), and typically 140-380 MPa (20.3-55.11 ksi), and more typically 145-350 MPa (21.03-50.76 ksi). In another non-limiting specific example, the magnesium composite alloy has a tensile yield strength of at least 241 MPa (35 ksi), and typically at least 310 MPa (45 ksi). In another non-limiting specific example, the magnesium composite alloy has an ultimate tensile strength (UTS) of 150-500 MPa (21.76-72.5 ksi), typically 160-400 (23.3-58 ksi), and more typically 160-350 MPa (23.3-50.76 ksi). In another non-limiting embodiment, the magnesium composite alloy has a ductility of at least 6% elongation to failure (Ef), typically a ductility of at least 8% Ef, more typically a ductility of at least 11% Ef, even more typically ductility of at least 15% Ef, and still even more typically ductility of at least 20% Ef. When the magnesium composite alloy is subjected to extrusion and heat treatment, the magnesium composite alloy can have yield strengths above 300 MPa (43.51 ksi), and even above 350 MPa (50.76 ksi), and with low compression-tensile ratios and greater than 8% Ef. The magnesium composite can have fatigue strengths above 200 MPa (29 ksi). Generally, the magnesium composite alloy will retain at least 70-80% of its physical room temperature (25° C.) properties at a temperature 150-250° C., and the magnesium composite alloy will retain at least 50% of its physical properties in at a temperature rate of 300° C. The magnesium composite alloy can have fatigue strengths that are greater than 250 MPa (36.26 ksi). Table 1 illustrates the physical properties of several magnesium composite alloys that includes 7-8.99 wt. % RE and at least 0.5 wt. % zinc.

TABLE 1

Test
UTS
YS
E^f
Test
UTS
YS
E_f

Alloy
Processing
Temp.
(ksi)
(ksi)
(%)
Temp.
(ksi)
(ksi)
(%)

Al
Solution
20° C.
33.7
21.4
3.5
150° C.
28.8
19.7
2.9

treat 20 hrs.

@ 500° C. -

Aged 16

hrs. @ 250° C.

A2
Solution
20° C.
31.9
18.2
11
150° C.
24
15.9
6

treat 20 hrs.

@ 500° C. -

Aged 16

hrs. @ 250° C.

A3
Solution
20° C.
34.5
22
20
150° C.
26.2
14.9
30.7

treat 20 hrs.

@ 500° C. -

Extruded

A4
Solution
20° C.
32.3
18.7
25
150° C.
24
14.5
37.3

treat 20 hrs.

@ 500° C. -

Extruded

A2
Solution
20° C.
38.5
22.1
18
150° C.
36.9
20
29

treat 20 hrs.

@ 500° C. -

Extruded

A5
Solution
20° C.
52.5
41.9
16
150° C.
45.2
36.2
24.3

treat 20 hrs.

@ 500° C. -

Extruded

A6
Solution
20° C.
42.9
26.6
22
150° C.
40.5
24.5
28.2

treat 20 hrs.

@ 500° C. -

Extruded

A7
Solution
20° C.
42.3
26.1
21
150° C.
39.4
22.8
32.7

treat 20 hrs.

@ 500° C. -

Extruded

In another non-limiting embodiment, the magnesium composite alloy has a thermal conductivity that is at least 170 W/m-K, and typically greater than 180 W/m-K, but less than 300 W/m K (and all values and ranges therebetween). The magnesium composite alloy exhibits lower texture and lower compression/tensile strength ratios than prior art magnesium alloys. Lower/weakened texture in turn leads to a lower (closer to 1:1) ratio of compression to tension yield strength. An extruded alloy of Mg-8.2Gd-3.8Y-1Zn-0.4Zr (wt. %) exhibited a ratio of 1.07. The magnesium composite alloy can be a substituted, quaternary magnesium alloy that exhibits high strength, UTS>47 ksi (325 MPa) and good processability, able to be extruded with an extrusion ratio (ER)>3 at a ram speed>6 inches per minute (2.54 mm/sec.)

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy contains 1) 5.01-8.99 wt. % rare earth metal, wherein the rare earth metal includes at least 2 wt. % yttrium and at least 1 wt. % gadolinium, 2) 0.5-3 wt. % zinc, and 3) at least two additional compound formers selected from zirconium, manganese, calcium, tin, and aluminum, and wherein the magnesium composite alloy is processed to produce an alloy with 10-60 vol. % LPSO phase (and all values and ranges therebetween), typically 15-50 vol. % LPSO phase, and at least 5 vol % (e.g., 5-40 vol. % and all values and ranges therebetween) of one or more secondary phase precipitates formed by precipitation (e.g., Mg-RE phase, non-RE precipitate phase). In one non-limiting specific example, about 90-100% of the one or more secondary phase precipitates formed by precipitation are formed by solid solution formation, and not through eutectic formation. In another non-limiting embodiment, precipitation in the magnesium composite alloy that is formed through eutectic formation is at least 90% reduced or eliminated by subjecting the magnesium composite alloy to a solutionization process. A high strength magnesium composite alloy can be formed by use of hot plastic deformation of at least 35% strain and typically 50-70% strain by traditional processes such as extrusion, rolling, forging, ECAP, stir processing, or other deformation technique.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is suitable for formation into minimum gauge thickness structures by rolling or extrusion. In one-non-limiting embodiment, the magnesium composite alloy can be rolled into sheets having a thickness of 5-100 mils (and all values and ranges therebetween). In one non-limiting specific example, the magnesium composite alloy can be rolled into sheets having a thickness of 20 mils. As can be appreciated, sheets having a thickness greater than 100 mills can also be formed. In another non-limiting specific example, the magnesium composite alloy can be rolled into sheets having a thickness of 10 mils. In another non-limiting specific example, the magnesium composite alloy can be rolled into sheets having a thickness of less than 200 mils.

In another non-limiting embodiment, the magnesium composite alloy can be extruded into components having small cross-sectional thickness. In one non-limiting specific example, the magnesium composite alloy can be extruded into components having cross-sectional thicknesses of less than 10 mm, typically 2 mm or less, more typically 1 mm or less, and still more typically 0.5 mm. As can be appreciated, components having cross-sectional thicknesses of greater than 10 mils can also be formed by extrusion. In another non-limiting embodiment, the magnesium composite alloy can be formed into complex profile by use of extrusion and with stretching from heated dies.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy comprises 1) at least 60 wt. % magnesium, typically at least 80 wt. % magnesium, and more typically at least 88 wt. % magnesium, 2) RE wherein a total content of RE is more than 5 wt. % and less than 9 wt. %, and wherein at least 2 wt. % RE contains yttrium, and wherein a majority the RE that does not include yttrium is gadolinium and/or neodymium, and wherein a weight ratio of non-yttrium RE to yttrium of 1:1 to 6:1 (and all values and ranges therebetween), and typically 5:4 to 3:2, and, 3) 0.5-3 wt. % zinc, and typically 0.8-1.5 wt. % zinc.

In another non-limiting aspect of the present disclosure, there is provided a cast or wrought magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy comprises 1) 5.01-8.99 wt. % RE, wherein the RE includes at least 2 wt. % yttrium and at least 1 wt. % gadolinium, 2) 0.5-3 wt. % zinc, 3) at least two compound formers selected from zirconium, manganese, calcium, tin, and aluminum, 3) a LPSO phase, wherein the LPPSO phase forms 15-40 vol. % of the magnesium composite alloy, and 4) a secondary phase precipitate formed of a magnesium-RE phase and/or a non-RE precipitate phase, wherein the secondary phase precipitate forms at least 5 vol. % of the magnesium composite.

In another non-limiting aspect of the present disclosure, several non-limiting examples of the magnesium composite alloy in weight percent are as follows:

Element
Ex. 1
Ex. 2
Ex. 3
Ex. 4
Ex. 5

Magnesium
60-97%
75-96.5%
80-95.4%
80-94.29%
82-93.99%

Zinc
0.5-7.99%
0.5-7%
0.6-6%
0.7-5%
1-3%

RE
2.5-16%
3-12%
4-10%
5.01-8.99%
5.01-8.99%

Zirconium
0-0.99%
0-0.99%
0-0.99%
0-0.99%
0-0.99%

Tin and/or
0-4%
0-4%
0-2%
0-2%
0-1%

Germanium

Aluminum
0-9.99%
0-7%
0-5%
0-4%
0-2%

Element
Ex. 6
Ex. 7
Ex. 8
Ex. 9
Ex. 10

Magnesium
60-97%
75-96.5%
80-95.4%
80-94.29%
82-93.99%

Zinc
0.5-7.99%
0.5-7%
0.6-6%
0.7-5%
1-3%

Gadolinium
0-15%
0.1-15%
0.1-10%
0.1-5%
0.1-3%

Yttrium
0-10%
0.1-10%
0.1-6%
0.1-4%
0.1-2%

Zirconium
0-0.99%
0-0.99%
0-0.99%
0-0.99%
0-0.99%

Tin and/or
0-2%
0-1%
0-1%
0-1%
0-1%

Germanium

Aluminum
0-9.99%
0-7%
0-5%
0-4%
0-2%

Element
Ex. 11
Ex. 12
Ex. 13
Ex. 14
Ex. 15

Magnesium
60-97%
75-96.5%
80-95.4%
80-94.29%
82-93.99%

Zinc
0.5-7.99%
0.5-7%
0.6-6%
0.7-5%
1-3%

Gadolinium
0-15%
0.1-15%
0.1-10%
0.1-5%
0.1-3%

Yttrium
0-10%
0.1-10%
0.1-6%
0.1-4%
0.1-2%

Zirconium
0-0.99%
0-0.99%
0-0.99%
0-0.99%
0-0.99%

Tin
0-2%
0-1%
0-1%
0-1%
0.01-1%

Germanium
0-2%
0-1%
0-1%
0-1%
0.01-1%

Aluminum
0-9.99%
0-7%
0-5%
0-4%
0-2%

Cerium
0-2%
0-2%
0.01-2%
0.1-2%
0.5-2%

Neodymium
0-4%
0-4%
0.01-3%
0.1-3%
0.1-2%

Zirconium
0-1.4%
0-1%
0.01-1%
0.1-0.8%
0.1-0.6%

Calcium
0-4%
0-3%
0-2%
0.01-1%
0.25-0.5%

Nickel
0-2%
0-2%
0-1%
0-1%
0-1%

Copper
0-2%
0-2%
0-2%
0-2%
0-20

Manganese
0-1.4%
0-1%
0.01-1%
0.1-0.8%
0.1-0.6%

Strontium
0-2%
0-1%
0-1%
0-1%
0.01-1%

Titanium
0-1%
0-1%
0-1%
0-1%
0-1%

Niobium
0-1%
0-1%
0-1%
0-1%
0-1%

Vanadium
0-1%
0-1%
0-1%
0-1%
0-1%

Dysprosium
0-4%
0-4%
0-3%
0-3%
0.01-2%

Erbium
0-4%
0-4%
0-3%
0-3%
0.01-2%

Lanthanum
0-2%
0-2%
0-2%
0-1%
0-1%

Europium
0-2%
0-2%
0-2%
0-1%
0-1%

Ytterbium
0-2%
0-2%
0-2%
0-1%
0-1%

In Examples 1-15, each of the magnesium composite alloys include 1) a LPSO phase, and 2) at least 2.5 wt. % RE. Typically, the magnesium composite alloys of Examples 1-15 also include a secondary phase precipitate that includes a magnesium-RE phase and/or a non-RE precipitate phase.

In one non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is formed of magnesium-RE-zinc.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy comprises 1) at least 60 wt. % magnesium, 2) RE wherein a total content of RE of at least 2.5 wt. % and 3) zinc.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy comprises at least 60 wt. % magnesium; more than 5 wt. % and less than 9 wt. % RE; at least 0.5 wt. % zinc; and wherein said magnesium composite alloy has a thermal conductivity that is at least 170 W/m-K, and/or has a ductility exceeding 6% elongation to failure.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy comprises at least 60 wt. % magnesium; 2.5-16 wt. % RE, said RE includes yttrium and/or gadolinium; and less than 8 wt. % zinc.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy comprises at least 60 wt. % magnesium; 2.5-16 wt. % RE, said RE includes yttrium and/or gadolinium; and less than 8 wt. % zinc; less than 1 wt. % zirconium; up to 1 wt. % tin; up to 1 wt. % germanium; and, less than 10 wt. % aluminum; and wherein the magnesium alloy composite includes a LPSO phase.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein said RE includes yttrium and non-yttrium RE, said non-yttrium RE includes gadolinium and/or neodymium, a weight ratio of non-yttrium RE to yttrium is about 1:1-10:, and typically 5:4 to 3:2.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein said RE includes 0.5-2 wt. % cerium and one or more other of said RE selected from the group consisting of gadolinium, neodymium, and/or yttrium.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein said RE includes more than 5 wt. % RE and less than 9 wt. % RE, said RE includes yttrium and non-yttrium rare earth metal, said RE includes 2-4 wt. % yttrium, at least 50% of said non-yttrium RE includes gadolinium, cerium, and/or neodymium, a weight ratio of non-yttrium RE to yttrium is 5:4 to 3:2.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy further includes a precipitate forming additive selected from calcium, aluminum, tin, zirconium, strontium, and manganese.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein a total of said LPSO phases in said magnesium composite alloy constitutes 2-60 vol. % of said magnesium composite alloy.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein a total of said LPSO phases in said magnesium composite alloy constitutes 5-50 vol. % of said magnesium composite alloy, and said magnesium composite alloy includes at least 5 vol. % of one or more secondary phase precipitates.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein a total of said LPSO phases in said magnesium composite alloy constitutes 20-40 vol. % of said magnesium composite alloy.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein a total of said LPSO phases in said magnesium composite alloy constitutes 5-20 vol. % of said magnesium composite alloy.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein a total of said LPSO phases in said magnesium composite alloy constitutes 5-40 vol. % of said magnesium composite alloy.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein a total of said secondary precipitate phases in said magnesium composite alloy constitutes 5-30 vol. % of said magnesium composite alloy.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy retains at least 85% of its of its room temperature (25° C.) strength properties at 150° C.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy has a tensile yield strength of greater than 280 MPa at 25° C., and/or an elongation to failure (Ef) of at least 6%.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy has a tensile yield strength of greater than 340 MPa at 25° C., and/or an Ef of at least 8%.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy has a tensile yield strength of greater than 350 MPa at 25° C., and/or an Ef of at least 8%.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy has a tensile yield strength of greater than 375 MPa at 25° C., and/or an Ef of at least 8%.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is direct chilled, sanded, and/or permanent mold cast, and then solutionized at 480-540° C. for at least 5 hours to partially or fully remove eutectic phases in said magnesium composite alloy.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is subject to an annealing precipitation/aging heat treatment for 4-50 hrs. at a temperature of 200-525° C.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is subject to a single stage heat treatment at 200-350° C. to co-precipitate said LPSO phase, and a magnesium-RE phase and/or a secondary precipitate phase.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is extruded at a rate of 2-15 inches/min at a temperature of 325-450° C., and thereafter optionally heat treated for at least 6 hrs. at a temperature that is ±25° C. said temperature of said extrusion.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy is subjected to a single-stage heat treatment process at a temperature of 200-350° C. to co-precipitate said LPSO phase and one or more of said secondary precipitate phases.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy includes at least two additional precipitates are present, including one rare earth of either Mg5RE (i.e., 5 wt. % RE in magnesium composite alloy) or Mg12RE (i.e., 12 wt. % RE in magnesium composite alloy) approximate composition.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the/magnesium composite alloy, wherein the magnesium composite alloy includes both a LPSO phase and an α-Mg phase, wherein both the LPSO phase and the α-Mg phase have an average major dimension of less than 50 microns.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy includes 1) at least 60 wt. % magnesium; 2) more than 5 wt. % and less than 9 wt. % RE; 3) at least 0.5 wt. % zinc; wherein said magnesium alloy contains at least 10% LPSO phase; and wherein at least one additional precipitate in addition to the LPSO phase is present in an amount at least 1 vol. %; and wherein said magnesium composite alloy has an ultimate tensile strength of at least 240 MPa and/or has a ductility exceeding 6% elongation to failure.

In another and/or alternative non-limiting object of the present invention, there is the provision of a magnesium composite alloy and a method for manufacturing the magnesium composite alloy, wherein the magnesium composite alloy includes 1) at least 60 wt. % magnesium; 2) 2.5-16 wt. % RE, said RE includes yttrium and/or gadolinium; 3) Zinc, said zinc is less than 8 wt. %; 4) up to 1 wt. % tin; 5) up to 1 wt. % germanium; and, 6) less than 10 wt. % aluminum; and wherein said magnesium alloy composite includes an LPSO phase.

Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be made to the drawings, which illustrate various embodiments that the invention may take in physical form and in certain parts and arrangements of parts wherein:

FIG. 1 are the images of a magnesium-RE-zinc magnesium composite alloy in accordance with the present disclosure at a magnification of 350×, 650×, and 3500×. At 350× and 650×, only the LPSO phase can be seen. At 3500×, both the LPSO phase and the secondary precipitate phase (i.e., intermetallic) can be seen. The average size of the each of the LPSO phases is illustrated to be about 10-20 μm in length (or maximum dimension) and the average size of each of the secondary precipitate phases is illustrated to be less than 1 μm in length (or maximum dimension).

FIGS. 3A-D illustrate Scheil and Equilibrium models for the min/max composition range of alloys 0010-1 and 0010-2.

FIG. 4 illustrates a phase diagram for a magnesium-zirconium system.

FIG. 5 illustrates a phase diagram for a magnesium-calcium system.

FIG. 6 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-5Gd-4Y-1Zn-xZr system.

FIG. 7 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-3 Gd-2Y-1Zn-xZr system.

FIG. 8 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-zirconium system corresponding to the vertical lines in FIG. 6.

FIG. 9 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-zirconium system corresponding to the vertical lines in FIG. 7.

FIG. 10 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-5Gd-4Y-1Zn-0.5Ca-xZr system.

FIG. 11 illustrates a PANDAT calculated equilibrium phase diagram isopleths for a magnesium-3Gd-2Y-1Zn-0.5Ca-xZr system.

FIG. 12 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-calcium-zirconium system corresponding to the vertical lines in FIG. 10.

FIG. 13 illustrates Scheil solidification models (PANDAT) in the magnesium-gadolinium-yttrium-zinc-calcium-zirconium system corresponding to the vertical lines in FIG. 11.

FIGS. 14A-C illustrate PANDAT Scheil and equilibrium calculations of fraction phase (mol %) for each of the five compositions listed in Table 4, 0010-3 a), 0010-4 b), 0010-5 c).

FIGS. 15A-C illustrate PANDAT Scheil and equilibrium calculations of fraction phase (mol %) for each of the five compositions listed in Table 4, 0010-6 a), 0010-7 b), 0010-8 c).

FIGS. 16A-C illustrate PANDAT Scheil and equilibrium calculations of fraction phase (mol %) for each of the five compositions listed in Table 4, 0010-9 a), 0010-10 b), 0010-11 c).

FIGS. 17A-C illustrate Scheil and equilibrium models through PANDAT for alloys MC181207-1, MC181214-1, and MC181221-1.

FIGS. 18A-C illustrate Scheil and equilibrium models through ThermoCalc for alloys MC181207-1, MC181214-1, and MC181221-1.

FIGS. 19A-B is a chart that illustrates the comparison of phase fractions between Scheil and equilibrium models for PANDAT and ThermoCalc of the alloys illustrated in FIGS. 17 and 18.

FIGS. 20A-C illustrate ternary isothermal sections in the magnesium-gadolinium-yttrium-zinc system of increasing zinc content at 500° C.

FIG. 21A-D illustrate ternary isothermal sections in for the magnesium-gadolinium-yttrium-0.10 at. % zinc system at various temperatures (200° C., 300° C., 400° C., 500° C.)

DETAILED DESCRIPTION OF THE DISCLOSURE

A more complete understanding of the articles/devices, processes, and components disclosed herein can be obtained by reference to the accompanying drawings. These figures are merely schematic representations based on convenience and the ease of demonstrating the present disclosure, and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.

Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.

The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions or processes as “consisting of” and “consisting essentially of” the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any unavoidable impurities that might result therefrom, and excludes other ingredients/steps.

Numerical values in the specification and claims of this application should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

All ranges disclosed herein are inclusive of the recited endpoint and independently combinable (for example, the range of “from 2 grams to 10 grams” is inclusive of the endpoints, 2 grams and 10 grams, and all the intermediate values).

The terms “about” and “approximately” can be used to include any numerical value that can vary without changing the basic function of that value. When used with a range, “about” and “approximately” also disclose the range defined by the absolute values of the two endpoints, e.g. “about 2 to about 4” also discloses the range “from 2 to 4.” Generally, the terms “about” and “approximately” may refer to plus or minus 10% of the indicated number.

Percentages of elements should be assumed to be percent by weight of the stated element, unless expressly stated otherwise.

Example 1

Two magnesium composite alloys were created by casting the magnesium composite alloy in a gas fired furnace in a plain carbon steel crucible. The total charge weight of the metals used to form the magnesium composite alloy was 450 g. 99.9% pure gadolinium, yttrium, and zinc when added to the magnesium. A fluoride flux was applied as a cover material prior to the start of heating. The temperature of the carbon steel crucible was 850-900° C. to facilitate in rapid melting of the RE. The crucible was cooled to 750° C. and slagged, stirred, and cast into a warm 150° C. cylindrical 1″ diameter molds. One magnesium composite alloy (0010-1) included 5 wt. % gadolinium, 4 wt. % yttrium, 1 wt. % zinc, and about 90 wt. % magnesium. The other magnesium composite alloy (0010-2) included 3 wt. % gadolinium, 2 wt. % yttrium, 1 wt. % zinc, and about 94 wt. % magnesium. FIG. 1 illustrates magnified regions of these two samples illustrating the formation of LPSO phases and secondary precipitate phases in both magnesium composite alloys.

Example 2

Magnesium composite alloys wherein one alloy included zirconium and the other two alloys included both calcium and zirconium were formed. When forming the magnesium-RE-zinc-zirconium alloy, magnesium was in the form of ingots, zirconium was added in the form of a master alloy of magnesium-30Zr wherein zirconium constituted 30 wt. % of the master alloy, gadolinium, and yttrium were shattered elemental pieces, and zinc was in the form of shot. When forming the magnesium-RE-zinc-calcium-zirconium alloy, calcium was added as shattered elemental pieces. When forming the magnesium composite alloys, the raw materials were charged into the plain carbon steel crucible at room temperature and approximately 50 mL of fluoride-containing flux was applied to the top surface of the raw materials. The temperature was raised using an electric band heater to 350° C. and allowed to settle for 30 min to allow moisture to evaporate from the surface of the raw materials. The temperature was then raised to 650° C. and allowed to sit for 30 min. The melt was raised slowly and allowed to sit idle at 780° C. for 45 min. The heater was turned off, the lid was removed at 780° C., and solid slag was removed from the surface of the melt. Approximately 5 g of C₂Cl₆degasser was submerged with the porous ladle and stirred into the melt. Alloy 1 contained 93.48 wt. % magnesium, 2.96 wt. % gadolinium, 1.98 wt. % yttrium, 0.98 wt. % zinc, and 0.59 wt. % zirconium. Alloy 2 contained 92.23 wt. % magnesium, 3.08 wt. % gadolinium, 2.04 wt. % yttrium, 1 wt. % zinc, 0.6 wt. % zirconium, and 1.05 wt. % calcium. Alloy 3 container 88.5 wt. % magnesium, 2.94 wt. % gadolinium, 1.99 wt. % yttrium, 3.05 wt. % zinc, 0.53 wt. % zirconium, and 3 wt. % calcium. Table 2 illustrates the properties of several of the formed magnesium composite alloys.

TABLE 2

HV
0.2% YS
UTS

Alloy
Processing
(kg/mm²)
(MPa)
(MPa)
E_f%

Mg-3Gd-2Y-1Zn-0.6Zr
AC
75.1-79.5

Mg-3Gd-2Y-1Zn-0.6Zr
AC + SOL-a
59.7-67.7

Mg-3Gd-2Y-1Zn-0.6Zr
AC + SOL-b
59.6-63.1

7

Mg-3Gd-2Y-1Zn-0.6Zr
AC + SOL-b +
64.6-75.6
112
208
13

AGE

Mg-3Gd-2Y-1Zn-0.6Zr
AC + EX-a
62.1-70.1
161-209
243-248
12-16

Mg-3Gd-2Y-1Zn-0.6Zr
AC + SOL-a +
62.3-81.2

EX-a

Mg-3Gd-2Y-1Zn-0.6Zr
AC + SOL-a +
74.2-76.5
238-239
283-285
16-17

EX-b

Mg-3Gd-2Y-1Zn-0.6Zr
AC + SOL-a +
75.3-88.3
194
301
7

EX-b + HR

Mg-3Gd-2Y-1Zn-0.6Zr-1Ca
AC
65.3-71.5

Mg-3Gd-2Y-1Zn-0.6Zr-1Ca
AC + SOL-a
65.3-73.4

Mg-3Gd-2Y-1Zn-0.6Zr-1Ca
AC + EX-a
65.5-70.4
169-170
245-245
12-14

Mg-3Gd-2Y-1Zn-0.6Zr-1Ca
AC + SOL-a +
81.3-86.4
176-180
250-255
15

EX-a

Mg-3Gd-2Y-1Zn-0.6Zr-1Ca
AC + SOL-a +
86.1-92.7
239-242
283-305
15-18

EX-b

Mg-3Gd-2Y-1Zn-0.6Zr-1Ca
AC + SOL-a +
84.8-96.3
200-223
270-305
2.5-4

EX-b + HR

Mg-3Gd-2Y-1Zn-0.6Zr-1Ca
AC + SOL-a +
96.9-111.7
163-179
296-310
6.5-8

EX-b + HR +

AGE

AC—As cast.

SOL-a—Solutionizing at 500° C. for 20 hrs. under argon.

SOL-b—Solutionizing at 545° C. for 22 hrs. under argon.

AGE—Aging treatment (200° C. for 23 hrs.).

EX-a—Round extrusion at 320° C., with an ER=10.3

EX-b—Flat extrusion at 400° C., with an ER=16.6 and with post extrusion quench.

HR—Hot rolling at 350° C. with a 50% reduction in thickness.

FIGS. 2A-D illustrate the microstructure of a magnesium-RE-zinc-zirconium magnesium composite alloy in accordance with the present disclosure. Three phases were observed in the magnesium composite alloy: (1) interdendritic block LPSO phases—FIG. 2B, (2) thin plate LPSO phases—FIG. 2C, and (3) some locations of RE-rich phases—FIG. 2D. The interdendritic block LPSO phase regions show increased segregation of zinc and gadolinium with some calcium and much less zirconium or yttrium. The thin plate-like LPSO precipitates are also visible in the microstructure especially close to the interdendritic LPSO regions. These are too thin to resolve elemental compositions of individual plates but they also appear to be calcium, zinc, and gadolinium with lesser zirconium or yttrium. There does not appear to be much in the way of thin plate LPSO in the matrix of the alloy. Finally, RE-rich phase regions are specifically enriched in zirconium and yttrium. These RE-rich regions are rather non-uniformly distributed as patches in the microstructure of the as-cast alloy.

Example 3

Two magnesium composite alloys were created by casting the magnesium composite alloy in a gas fired furnace in a plain carbon steel crucible. The total charge weight of the metals used to form the magnesium composite alloy was 50 lbs. 99.9% pure gadolinium, yttrium, and zinc when added to the 99.9% pure magnesium. Pure magnesium was charged into the crucible and brought to 760° C. under inert (mixture SF₆/CO2/air) atmosphere. Gadolinium and yttrium were added and stirred. After dissolution of the RE, approximately 15 minutes, the melt for each casting was degassed (C₂Cl₆at a ratio of 1 g/1 lb. melt), slagged, and poured into an A36 steel permanent mold (7″×7″×4″ block). The first magnesium composite alloy included 10.4 wt. % gadolinium, 3.6 wt. % yttrium, 2.9 wt. % zinc, and 83.1 wt. % magnesium. The second magnesium composite alloy included 10.2 wt. % gadolinium, 4.7 wt. % yttrium, 5.1 wt. % zinc, and 80 wt. % magnesium. Both magnesium composite alloys were homogenized at 500° C. for 17 hours and water quenched. The magnesium composite alloys were subsequently aged at 225° C. for 24 hrs. The Rockwell B hardness of the first magnesium composite alloy after aging was 22-30 and the Rockwell B hardness of the second magnesium composite alloy was 32-36. The UTS of the first magnesium composite alloy after aging was 230 MPa with an elongation to failure of 7%.

Compositions for CALPHAD models are found in TABLE 3. The compositions were converted to at % (atomic percent) and the values of Gd+Y and (Gd+Y)/Zn were computed for each of the four compositions. These values are used empirically to rate the magnitude of LPSO and intermetallic formation. Scheil (rapid) and Equilibrium (slow) cooling models were completed through PANDAT for each of the four compositions. The concentration of species (mol fraction) for the equilibrium cooling is also set forth in TABLE 3. For the two alloys under equilibrium conditions, there is a range of mol fraction 0.043-0.053 (or approximately 4-5%) for the LPSO content. According to the PANDAT predictions, the fraction of LPSO is relatively equal between 10-1 and 10-2. The SEM/EDX maps, however, much more closely match the Scheil solidification curves presented in FIG. 3 with 10-1 having a fraction LPSO of 4-5% and 10-2 of 2-3%. The RMg₅and R5Mg24 intermetallic phases are also predicted according to the Scheil model in very dilute concentrations. The RMg₅and R5Mg24 intermetallic phases may be gadolinium and/or yttrium-containing intermetallics.

TABLE 3

Comp.
Mg
Gd
Y
Zn
Gd + Y
(Gd + Y)/Zn
LPSO
RMg₅
R₅Mg₂₄

10-1a
wt. %
92.04
4.3
2.8
0.86
—
—
0.047
0.045
0.017

at. %
98.13
0.71
0.82
0.34
1.52
4.47

10-1b
wt. %
90.49
4.8
3.8
0.91
—
—
0.051
0.051
0.034

at. %
97.71
0.8
1.12
0.37
1.92
5.26

10-2a
wt. %
94.72
2.6
1.9
0.78
—
—
0.043
0.024
0.008

at. %
98.74
0.42
0.54
0.3
0.96
3.18

10-2b
wt. %
93.74
3.2
2.1
0.96
—
—
0.053
0.03
0.007

at. %
98.50
0.52
0.6
0.38
1.12
2.99

The results set forth in TABLE 3 indicate the strong role thermal history plays in the development of a preferred microstructure as well as the power of thermodynamic modeling to predict said microstructures.

The 10-1 and 10-2 compositions were used as a baseline to examine the effect of microalloying zirconium and calcium content. Both equilibrium phase diagrams and Scheil solidification curves were modeled through PANDAT. Example phase diagrams for magnesium-zirconium and magnesium-calcium are shown below in FIGS. 4-5. Calcium was either present (0.5 wt. % in the compositions) or was absent. Zirconium content was varied in the equilibrium phase diagram from 0-1 wt. %. Scheil solidification curves were calculated assuming a zirconium concentration of 0.5 wt. %.

The equilibrium phase diagrams for zirconium content varied between 0-1 wt. % are presented in FIGS. 6-7 for two different magnesium composite alloys. As both alloys are dilute in RE and zinc, the diagrams are similar to the magnesium-zirconium binary diagram. The boundary for the formation of α-Zr (HCP) is shifted to a lower weight percent (0.4 wt. % zirconium) than the magnesium-zirconium binary (0.565 wt. %). This indicates that less supersaturated zirconium is required in solution at elevated temperatures (750-800° C.) to facilitate in enhanced nucleation of α-Mg (HCP) grains. The liquidus temperature of the alloy is depressed slightly from the magnesium-zirconium binary and the liquid+α-Mg (HCP) phase field has opened. Both alloys are predicted to have the same phases α-Mg (HCP), α-Zr (HCP #2), R5Mg24, RMg5, and R8Mg70Zn6_14H (LPSO) present in equilibrium at room temperature. Both R5Mg24 and RMg5 are predicted to dissolve back into solution at lower temperatures for the lower RE content Mg-3Gd-2Y-1Zn-xZr than the higher RE content Mg-5Gd-4Y-1Zn-xZr. Likewise, the LPSO is stable to a higher temperature in the higher RE content alloy, indicating superior high temperature strength. Scheil models were also calculated for the compositions Mg-3Gd-2Y-1Zn-0.5Zr and Mg-5Gd-4Y-1Zn-0.5Zr as illustrated in FIGS. 8-9. Under rapid cooling conditions, the α-Zr (HCP_#2) phase is not expected to form, despite the high concentration of zirconium in the alloys. It should also be noted that neither of these alloys is expected to have a single phase α-Mg (HCP) condition at any temperature, indicating challenges to solutionizing the alloys during heat treatment. The RM3_W phase (a brittle intermetallic) is present at very high temperatures.

Scheil models were completed for the compositions with the addition of 0.5 wt % calcium as illustrated in FIGS. 10 and 11. The liquidus remains relatively the same, but the solidus is further depressed. There is a new phase Mg2Ca (C14) the laves phase from the magnesium-calcium binary diagram. This phase is stable to its eutectic temperature of 516° C. While the addition of the laves phase may prove beneficial to the strengthening of the alloy, it lowers the solidus temperature, thereby making elevated temperature processing such as extrusion more challenging. Again, the Scheil models indicate that the α-Zr (HCP) phase does not form on rapid cooling. Although rapid cooling would assist in formation of a small, uniform grain size, the effect of zirconium nucleation of grains would not be present in the alloys.

An additional thermodynamic (ThermoCalc) assessment of the magnesium-gadolinium-yttrium-zinc quaternary system was performed with dilute as well as high concentrations of rare earth to evaluate the effect of varying the gadolinium/yttrium ratio on LPSO and intermetallic formation. The ratio of 5/2 was held constant as well as the magnitude of RE for this dilute model work. Both Scheil and Equilibrium models were completed for the alloys. From this work it was found that LPSO content depends both on the magnitude of the RE content as well as the above-mentioned ratio. Additionally, the intermetallic RMg5 is favored for high gadolinium content whereas R5Mg24 is favored for high yttrium content.

Further PANDAT models were evaluated with a high RE content (total Gd+Y of 4 at %, see TABLE 4. The ratio of (Gd+Y)/Zn was varied by increasing zinc content from 1 to 2 at %. As the zinc content increases (and the ratio of (Gd+Y)/Zn decreases) there is a significant increase in the predicted LPSO content. Similar to the dilute alloy calculations, as the ratio of gadolinium/yttrium changes, the relative concentration of RMg5 and R5Mg24 change as well.

TABLE 4

Comp.
Mg
Gd
Y
Zn
Gd + Y
(Gd + Y)/Zn
LPSO
RMg₅
R₅Mg₂₄

10-3
wt. %
80.46
5.54
9.39
4.61
—
—
0.2803
0.0274
0.0512

at. %
94
1
3
2
4
2

10-4
wt. %
78.57
10.82
6.12
4.5
—
—
0.2802
0.0794
—

at. %
94
2
2
2
4
2

10-5
wt. %
76.77
15.85
2.99
4.39
—
—
0.2797
0.0799
—

at. %
94
3
1
2
4
2

10-6
wt. %
81.48
5.58
9.46
3.48
—
—
0.21
0.0389
0.0797

at. %
94.5
1
3
1.5
4
2.7

10-7
wt. %
79.55
10.89
6.16
3.4
—
—
0.2102
0.1155
0.0034

at. %
94.5
2
2
1.5
4
2.7

10-8
wt. %
77.71
15.96
3.01
3.32
—
—
0.21
0.12
—

at. %
94.5
3
1
1.5
4
2.7

10-9
wt. %
82.51
5.62
9.53
2.34
—
—
0.14.02
0.0503
0.1079

at. %
95
1
3
1
4
4

10-10

80.55
10.97
6.2
2.28
—
—
0.1399
0.1271
0.0318

95
2
2
1
4
4

10-11

78.67
16.07
3.03
2.23
—
—
0.1401
0.1594
—

95
3
1
1
4
4

At these high RE contents, the RM3_W phase is predicted almost always for rapid (Scheil) cooling conditions. Under equilibrium conditions, the R8Mg70Zn6_14H (LPSO) phase is stable very near the solidus and may even be stable with the liquid. This indicates that these alloys would be amenable to high temperature operation. Solutionizing to single phase α-Mg would not be possible for these alloys. (See FIGS. 14-16).

Scheil and eqilbrium models were completed for three of the alloys (MC181207-1, MC181214-1 and MC181221-1) as illustrated in TABLE 5.

TABLE 5

Mg
Gd
Y
Zn

Sample
(wt. %)
(wt. %)
(wt. %)
(wt. %)

MC181207-1
82.98
10.4
3.62
3.00

MC181214-1
81.73
10.57
5.25
2.45

MC181221-1
79.95
10.2
4.74
5.1

FIGS. 17A-C and FIGS. 18A-C illustrate PANDAT and ThermoCalc diagrams. The PANDAT predicts a phase called RM3_W in the Scheil condition for all three alloys that is defined as Mg0.25(Gd,Y)0.25(Mg,Zn)0.5. Thermo-Calc also predicts a similar phase called L12_RMGZN2, defined as Mg1(Gd,Y)1(Mg,Zn)2, for the MC21 alloy in the Scheil condition. A summary of the phase fractions for both sets of models is found in the chart illustrated in FIG. 19. The chart illustrates that there is significant (˜40% mol fraction as modeled through ThermoCalc and ˜30% mol fraction as modeled through PANDAT) LPSO expected to form in alloy MC181221-1.

A thermodynamic assessment was taken of dilute magnesium-gadolinium-yttrium-zinc alloys to identify likely composition space where a full solutionizing anneal (single phase α-Mg) is feasible. A series of ternary isothermal sections in the magnesium-gadolinium-yttrium-zinc quaternary system were created through PANDAT for increasing zinc composition as illustrated in FIGS. 20-21. The ovals highlighted in the 0.05 at % zinc and 0.10 at % zinc isothermal sections indicate composition space likely to facilitate a full solutionizing treatment. The oval in the 0.05 at % zinc isothermal section has further been identified as 3-6 wt. % gadolinium, 0.2-0.7 wt. % yttrium, and 0.15 wt. % zinc. Further equilibrium isothermal sections have been completed for the magnesium-gadolinium-yttrium Y-0.10 at % zinc system. The region highlighted by the oval appears to facilitate solutionizing (avoiding the formation of the RM3 W phase completely and the LPSO 14H phase at 500° C.). Additionally, it experiences RMg5 precipitation at 200° C. An analysis such as this would prove powerful in development of an alloy system (possibly such as magnesium-gadolinium-neodymium or magnesium-gadolinium-yttrium) which can be solutionized and/or processed at high temperature with subsequent precipitation hardening sequence with a lower temperature aging treatment.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The invention has been described with reference to preferred and alternate embodiments. Modifications and alterations will become apparent to those skilled in the art upon reading and understanding the detailed discussion of the invention provided herein. This invention is intended to include all such modifications and alterations insofar as they come within the scope of the present invention. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention, which, as a matter of language, might be said to fall there between. The invention has been described with reference to the preferred embodiments. These and other modifications of the preferred embodiments as well as other embodiments of the invention will be obvious from the disclosure herein, whereby the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims.

High Strength Microalloyed Magnesium Alloy

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