Patent Application
20190032180
This invention relates to aluminum-copper-lithium alloy wrought products, and more particularly Al—Cu—Li alloy compositions and processing methods that provide extruded products having improved properties.
Conventional aluminum-lithium alloys often contain copper, magnesium, and may also contain manganese and/or zirconium in some cases. Aluminum alloys containing lithium additions are beneficial because lithium reduces the density of aluminum alloys by about three percent and increases the modulus of elasticity by about five percent for every weight percent of lithium added. However, the addition of lithium to aluminum alloys may also result in a decrease in ductility and fracture toughness. For use in aircraft parts and aerospace components an alloy should have excellent fracture toughness and strength properties, but it will be appreciated that both high-strength and high-fracture toughness are difficult to obtain in conventional alloys. Furthermore, in order for lithium-containing aluminum alloys to be selected for aerospace or aircraft components, their performance must reach that of alloys commonly used, particularly in the compromise between static mechanical strength and damage tolerance, which are generally antinomic. Said alloys must also have good corrosion resistance. It will be appreciated that the alloys must also be processed in a manner to adequately control the balance of strength, toughness, corrosion resistance, and density.
Materials cost is a major concern in the aerospace industry. One method to reduce the cost of extruded aluminum alloy products is to cut down on the raw material cost. The addition of silver, especially in the presence of magnesium, has proven beneficial in aluminum-copper-lithium alloys. For example, silver is intentionally added to registered aluminum-copper-lithium alloys AA2050, AA2055, AA2075, AA2085, AA2094, AA2095, AA2195, AA2295, AA2395, AA2196, AA2296, AA2098, and AA2198, but silver additions can add significant raw materials costs to a product. Therefore, a more desirable alloy would be essentially silver-free with silver only being an impurity. It will be appreciated that a silver-free aluminum-copper-lithium alloy that still maintains high strength levels, high fracture toughness, and low density would be a desirable aluminum-copper-lithium product.
The present invention provides improved aluminum based alloys containing lithium and methods of making extruded products therefrom. The alloy may be provided as a wrought aluminum-copper-lithium extrusion having improved combinations of strength, fracture toughness, corrosion resistance, and relatively low density. The alloy may include, in weight percent, 2.6-3.0 Cu, 1.4-1.75 Li, 0.10-0.45 Mg, 0.0-0.25 Mn, 0.05-0.15 Zr, and the balance aluminum and incidental impurities. The alloy may be essentially Ag-free, with Ag only being present as an impurity at an amount less than or equal to 0.05 weight percent. Furthermore, the alloy may only include a maximum weight percent of Zn of 0.20. The aluminum-copper-lithium alloys may be provided in the form of extruded products having improved combinations of strength and fracture toughness.
An aspect of the present invention is to provide an extruded aluminum alloy product comprising from, in weight percent, 2.6-3.0 Cu, 1.4-1.75 Li, 0.1-0.45 Mg, 0-0.25 Mn, 0.2 max Zn, 0.05 max Ag, 0.1 max Si, 0.12 max Fe, 0.05-0.15 Zr, 0-0.1 Ti, and the balance Al and incidental impurities, wherein the extruded aluminum alloy product comprises ≤25% recrystallized grains, and has a L-T fracture toughness KQ of at least 34 ksi √in and a L tensile yield strength of at least 72 ksi.
Another aspect of the present invention is to provide an extruded aluminum alloy product comprising from, in weight percent, 2.6-3.0 Cu, 1.4-1.75 Li, 0.1-0.45 Mg, 0-0.25 Mn, 0.2 max Zn, 0.05 max Ag, 0.1 max Si, 0.12 max Fe, 0.05-0.15 Zr, 0-0.1 Ti, and the balance Al and incidental impurities, wherein the extruded aluminum alloy product comprises ≤25% recrystallized grains, and has a T-L fracture toughness KQ of at least 33 ksi √in and a L-T tensile yield strength of at least 67 ksi.
A further aspect of the present invention is to provide an extruded aluminum alloy product comprising from, in weight percent, 2.8-3.0 Cu, 1.4-1.6 Li, 0.1-0.25 Mg, 0.05 max Mn, 0.2 max Zn, 0.05 max Ag, 0.05 max Si, 0.07 max Fe, 0.09-0.13 Zr, 0-0.06 Ti, and the balance Al and incidental impurities, wherein the extruded aluminum alloy product comprises ≤25% recrystallized grains, and has a L-T fracture toughness KQ of greater than 42 ksi √in.
A further aspect of the present invention is to provide an extruded aluminum alloy product comprising from, in weight percent, 2.7-2.9 Cu, 1.55-1.75 Li, 0.3-0.4 Mg, 0.1-0.2 Mn, 0.2 max Zn, 0.05 max Ag, 0.05 max Si, 0.07 max Fe, 0.09-0.13 Zr, 0-0.06 Ti, and the balance Al and incidental impurities, wherein the extruded aluminum alloy product comprises ≤25% recrystallized grains, and has a L tensile yield strength greater than 74 ksi.
Another aspect of the present invention is to provide a method of making an extruded aluminum alloy product comprising from, in weight percent, 2.6-3.0 Cu, 1.4-1.75 Li, 0.1-0.45 Mg, 0-0.25 Mn, 0.2 max Zn, 0.05 max Ag, 0.1 max Si, 0.12 max Fe, 0.05-0.15 Zr, 0-0.1 Ti, and the balance Al and incidental impurities, wherein the extruded aluminum alloy product has less than or equal to 25% recrystallized grains, the method comprising homogenizing a cast billet or shape of the aluminum alloy, hot working the billet or shape into an extruded product, subjecting the extruded product to a solution heat treatment at a temperature of from 940° F. to 1020° F., quenching the solution heat treated extruded product, stretching the extruded product to a permeant set of 3-9%, and artificially aging the extruded product by heating to at least one temperature of from 290° F. to 315° F. for 36-100 hours.
A further aspect of the present invention is a method of making an extruded aluminum alloy product comprising from, in weight percent, 2.6-3.0 Cu, 1.4-1.75 Li, 0.1-0.45 Mg, 0-0.25 Mn, 0.2 max Zn, 0.05 max Ag, 0.1 max Si, 0.12 max Fe, 0.05-0.15 Zr, 0-0.1 Ti, and the balance Al and incidental impurities, wherein the extruded aluminum alloy product has less than or equal to 25% recrystallized grains, the method comprising homogenizing a cast billet or shape of the aluminum alloy, hot working the billet or shape into an extruded product, subjecting the extruded product to a solution heat treatment at a temperature greater than or equal to 970° F., quenching the solution heat treated extruded product, stretching the extruded product to a permeant set of 3-9%, and artificially aging the extruded product by heating to at least one temperature of from 290° F. to 315° F. for 12-36 hours.
These and other aspects of the present invention will be more apparent from the following description.
Unless otherwise specified, all the indications relating to the chemical composition of the alloys are expressed as percentage by weight based on the total weight of the alloy. References to commercially known alloys, when applicable, are named in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The density of an alloy depends on its composition and can be calculated, when not physically measured, in accordance with The Aluminum Association procedure, which is described on pages 2-12 and 2-13 of “Aluminum Standards and Data 2013.” The definitions of alloy tempers are also given in “Aluminum Standards and Data 2013” on pages 1-6 through 1-10.
It is also known that the orientations of extruded sections are based on the localized grain flow in the extruded section, and therefore in complex extrusions there is no global orientation system governing the entire extruded body. It is also known that regions in complex extrusions can have complex grain flows which cannot be easily defined by a simple orientation system. These regions are defined herein as transition zones, and when tested can potentially exhibit mechanical properties akin to those tested in off-axis orientations depending on several factors including sample location, sample size, grain flow, and testing direction. The transition zones are created at the intersection of various extrusion features. For example, transition zones may be formed at joints or different legs of the same extrusion. As shown in
The transition zones may exhibit poor mechanical properties, e.g., ductility, depending on the interaction between localized grain flow and part machining/loading. The extrusions of the present invention include an improved combination of properties throughout the entire extruded body, including the transition zones, that may provide the extrusions with an enhanced resistance to failure.
The present invention provides aluminum based alloys suitable for forming into extruded products having improved combinations of strength, fracture toughness, and corrosion resistance, with a density between 0.094-0.096 lbs/in3, for example, about 0.095 lbs/in3. The alloys may comprise, in weight percent, 2.6-3.0 Cu, 1.4-1.75 Li, 0.10-0.45 Mg, 0.0-0.25 Mn, 0.20 max Zn, 0.05 max Ag, 0.10 max Si, 0.12 max Fe, 0.05-0.15 Zr, and 0-0.10 Ti with minor impurities also present. These compositional ranges are listed as embodiment I in Table 1.
In certain embodiments, the alloys of the present invention can contain, in weight percent, 2.8-3.0 Cu, 1.4-1.6 Li, 0.10-0.25 Mg, 0.05 max Mn, 0.20 max Zn, 0.05 max Ag, 0.05 max Si, 0.07 max Fe, 0.09-0.13 Zr, and 0-0.06 Ti. The balance aluminum and minor impurities. The calculated density of the alloy composition in accordance with this embodiment may be about 0.0952 lbs/in3. The alloy of the present invention could also optionally contain Sc up to 0.40 weight percent. These compositional ranges are listed as embodiment II in Table 1.
An alloy composition in accordance with an embodiment of the present invention may contain, in weight percent, 2.8-3.0 Cu, 1.4-1.6 Li, 0.15-0.25 Mg, 0.05 max Mn, 0.05 max Zn, 0.05 max Ag, 0.05 max Si, 0.05 max Fe, 0.09-0.13 Zr, and 0-0.05 Ti. The balance aluminum and minor impurities. The calculated density of the alloy composition in accordance with this embodiment may be about 0.0954 lbs/in3. These compositional ranges are listed as embodiment III in Table 1.
A specific example of an alloy composition within the compositional ranges of embodiments II and III may contain, in weight percent, 2.89 Cu, 1.54 Li, 0.2 Mg, 0.04 Mn, 0.01 Zn, 0 Ag, 0.04 Si, 0.03 Fe, 0.1 Zr, and 0.03 Ti. The balance aluminum and minor impurities. This example alloy composition is listed as embodiment IV in Table 1.
An alloy composition in accordance with an embodiment of the present invention may contain, in weight percent, 2.7-2.9 Cu, 1.55-1.75 Li, 0.3-0.4 Mg, 0.1-0.2 Mn, 0.2 max Zn, 0.05 max Ag, 0.05 max Si, 0.07 max Fe, 0.09-0.13 Zr, and 0-0.06 Ti. The balance aluminum and minor impurities. The calculated density of the alloy composition in accordance with this embodiment may be about 0.0953 lbs/in3. These compositional ranges are listed as embodiment V in Table 1.
Another alloy composition in accordance with an embodiment of the present invention may contain, in weight percent, 2.7-2.9 Cu, 1.6-1.7 Li, 0.3-0.4 Mg, 0.1-0.2 Mn, 0.05 max Zn, 0.05 max Ag, 0.05 max Si, 0.05 max Fe, 0.09-0.13 Zr, and 0-0.05 Ti. The balance aluminum and minor impurities. The calculated density of the alloy composition in accordance with this embodiment may be about 0.0949 lbs/in3. These compositional ranges are listed as embodiment VI in Table 1.
A specific example of an alloy composition within the compositional ranges of embodiments V and VI may contain, in weight percent, 2.75 Cu, 1.54 Li, 0.36 Mg, 0.13 Mn, 0 Zn, 0 Ag 0.03 Si, 0.05 Fe, 0.11 Zr, and 0.03 Ti. The balance aluminum and minor impurities. This example alloy composition is listed as embodiment VII in Table 1.
In the present invention, Li improves tensile and yield strengths as well as elastic modulus in addition to permitting a significant decrease in density. Additionally, Li additions may improve fatigue resistance. In accordance with certain embodiments, the addition of Li can result in an aluminum based alloy with a unique combination of strength and toughness while maintaining meaningful reductions in density.
In certain embodiments, the addition of Cu, particularly in the ranges set forth herein above for use in accordance with the present invention, provides the capability of yielding high strength and fracture toughness. In accordance with certain embodiments, the Cu content may be selected to develop an alloy with a desirable combination of strength and toughness without sacrificing density.
While the inventors do not wish to be held to any theory of invention, it is believed the improved combinations of strength and toughness are due to the desired precipitation of the T1 phase over δ-type precipitates, which could be due to maintaining a high Cu:Li ratio. In accordance with certain embodiments, the Cu:Li ratio may be greater than 1.45:1, or greater than 1.6:1. For example, the Cu:Li ratio may range from 1.6:1 to 2.15:1, or from 1.65:1 to 2.0 to 1.
In certain embodiments, Mg may be added to increase strength, although additions of Mg do slightly decrease density. It is important to control Mg additions as excess Mg can lead to poor fracture toughness through the formation of undesirable phases at the grain boundaries. Although additions of Mn can be added as a grain structure controlling element, in certain embodiments low Mn levels may be utilized for the purpose of mainly solid solution strengthening. Even though Mn-type dispersoids and other intermetallic phases may be present in the microstructure they are not the purpose of the alloying addition. It is desirable to retain Mn in solid solution in the final extruded product as much as possible.
While not intending to be bound by any particular theory, it is believed that having low Mn (less than 0.25 weight percent) avoids the formation of AlxMnXCuX-type dispersoids, and allows more Cu to be available for the formation of the T1 phase. Similarly, it is believed that having low Mg levels (0.10-0.45 weight percent) avoids the formation of S-phase (Al2CuMg)-type phases also freeing up Cu for the formation of the T1 phase. Conversely, Mg additions are believed to aid in the formation of the T1 phase due to its high vacancy binding energy. Therefore, it is apparent that an optimum balance of Mg must be achieved to maximum the T1 phase present in an Al—Cu—Li alloy. Having low levels of Mg and Mn can lead to low work hardening and improve toughness with a loss in strength. In certain embodiments, in order to improve strength, Mn can be added in levels just high enough to provide solid solution strengthening and to aid in work hardening. Likewise, Mg can also be added to assist in the formation of T1 and increase the work hardening ability of the alloy.
In certain embodiments, Zr may be added as a grain structure controlling element, although other grain controlling materials such as Sc, Ti, Hf, Cr, or combinations thereof could be utilized. The amount of Zr alloyed into a product is dictated by whether a recrystallized or unrecrystallized grain structure is desired.
The aluminum-copper-lithium extruded products may be substantially free of Ag. As used herein, the term “substantially free” when referring to alloying additions, means that a particular element or material is not purposefully added to the alloy, and is only present, if at all, in minor amounts as an impurity. For example, in impurity amounts of less than 0.05 weight percent, or less than 0.02 weight percent, or less than 0.01 weight percent.
In certain embodiments, Zn may optionally be added to Al—Cu—Li alloys to improve strength and corrosion resistance as long as the Mg:Zn ratio is less than 1. However, Zn can also increase the density of an alloy, and in embodiments of the present invention should be kept below 0.2 weight percent. In certain embodiments, the aluminum-copper-lithium extruded products may be substantially free of Zn.
Extruded products made from Al—Cu—Li alloys of the present invention have been found to possess favorable properties including improved combinations of strength and fracture toughness, improved corrosion resistance, and relatively low density.
Unless mentioned otherwise, static mechanical characteristics, in other words the ultimate tensile strength (UTS), tensile yield strength (TYS), and the elongation at fracture (e), are determined by a tensile test according to standard ASTM B557—Standard Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products.
Unless mentioned otherwise, fracture toughness is evaluated according to ASTM B645—Standard Practice for Linear-Elastic Plane-Strain Fracture Toughness Testing of Aluminum Alloys. ASTM B645 also references ASTM E 399—Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness K1C of Metallic Materials.
As used herein, the term “exfoliation corrosion rating” means results corresponding to MASTMASSIS corrosion testing done according to ASTM G85—Annex 2. Resistance to exfoliation corrosion may be evaluated by exposing the aluminum based alloys according ASTM standard G85—Standard Practice for Modified Salt Spray (FOG) Testing, specifically Annex 2—Cyclic Acidified Salt Fog Testing, and the results were evaluated according to ASTM standard G34—Standard Test Method for Exfoliation Corrosion Susceptibility in 2xxx and 7xxx Series Aluminum Alloys. The samples were exposed according to ASTM G85—Annex 2 instead of ASTM G34 as the corrosion resistance of Al—Cu—Li type alloys during seacoast exposure cannot be correlated to ASTM G34 exposures as shown by Morin et al. “Improvements in corrosion resistance offered by newer generation 2×99 aluminum-lithium alloys for aerospace applications” from The Proceedings of the 12th International Conference on Aluminum Alloys, p. 1492-1497, 2010, and Morin et al. “Corrosion performance of new generation aluminum-lithium alloys for aerospace applications” from The Proceedings of the 13th International Conference on Aluminum Alloys, p. 425-430, 2012.
Unless mentioned otherwise, resistance to intergranular corrosion (IGC) is evaluated according to ASTM G110—Standard Practice for Evaluating Corrosion Resistance of Heat Treatable Aluminum Alloys by Immersion in Sodium Chloride+Hydrogen Peroxide Solution. For IGC testing, the maximum depth of attack in μm and the frequency of IGC attack (number of attacks per inch) were calculated.
Unless mentioned otherwise, cryogenic tensile and cryogenic fracture testing refers to testing performed at −320° F.
Unless mentioned otherwise, three-point bend testing is performed according to standard BS EN 2563 (1997). The displacement of the loading nose is defined herein as d. In accordance with an embodiment of the present invention, the three-point bend testing may be performed at transition zones and provide an off-axis three-point bend displacement d value. The three-point displacement d may provide the final displacement at failure.
Unless mentioned otherwise, fatigue testing is performed according to ASTM E466-15—Standard Practice for Conducting Force Controlled Constant Amplitude Axial Fatigue Tests of Metallic Materials, using open hole Kt of 2.3 and T-type specimens with a minimum/maximum load ratio R of 0.1 at a frequency of 30 Hz.
Unless mentioned otherwise, fatigue crack growth rate testing is performed according to ASTM E647-15—Standard Test Method for Measurement of Fatigue Crack Growth Rates, using CC(t) center crack tension specimens with a nominal width (W) of 4 in and thickness (B) of 0.2 in. The specimens are pre-cracked and then tested at room temperature with a stress ratio of 0.1 at a cyclic frequency of 10 Hz. Specimens are tested in either a lab air (humidity 26-42%) or a humid air (humidity >90%) environment.
In accordance with certain embodiments, the extruded aluminum alloy products of the present invention may have a L-T fracture toughness KQ of at least 34 ksi √in and a L tensile yield strength of at least 72 ksi. In certain embodiments, the extruded aluminum alloy products of the present invention may have a L-T fracture toughness KQ greater than 40 ksi √in and a L tensile yield strength greater than 75 ksi. In other embodiments, the extruded aluminum alloy products of the present invention may have a T-L fracture toughness KQ of at least 33 ksi √in and a L-T tensile yield strength of at least 67 ksi.
In accordance with certain embodiments, desirable combinations of fracture toughness and tensile yield strength are achieved. For example, the combination of L-T fracture toughness KQ (ksi √in) and L tensile yield strength (ksi) may be greater than or equal to the following equation: L-T KQ>38−2.5*[L TYS−76]. Similarly, the combination of T-L fracture toughness KQ and L-T tensile yield strength may be improved. As more fully described below, extruded aluminum alloy products in accordance with embodiments of the invention have been found to produce such improved combinations of fracture toughness and tensile yield strength.
In accordance with certain embodiments, the extruded aluminum alloy products of the present invention may have an off-axis three-point bend displacement d measured at a transition zone of greater than 0.55 mm, or greater than 0.6 mm, or greater than 0.75 mm, or greater than 0.95 mm, or at least 0.99 mm.
In accordance with certain embodiments, the extruded aluminum alloy products of the present invention may have a cryogenic L-T fracture toughness K1C of greater than 47 ksi √in, for example, greater than 48.5 ksi √in.
In accordance with certain embodiments, the extruded aluminum alloy products of the present invention may have an exfoliation corrosion rating of at least EB. For example, the extruded aluminum alloy products may have an exfoliation corrosion rating of EA.
In accordance with certain embodiments, the extruded aluminum alloy products of the present invention may have a L elongation of at least 9.5 percent, for example, greater than 10.5 percent.
In accordance with certain embodiments, the extruded aluminum alloy products of the present invention may have a L tensile yield strength of at least 64 ksi and a L-T fracture toughness KQ of at least 60 ksi √in. In certain embodiments, the extruded aluminum alloy products may have a fatigue crack growth rate less than or equal to 1E-8 (ΔK)̂2.4994 when Δk=30-50 ksi √in.
In accordance with an embodiment of the present invention, the extrusion may be formed as a high toughness composition listed as embodiment II in Table 1. By including a relatively small addition of Mn in an amount of 0.05 weight percent or less when extruded into the body shown in
In certain embodiments, location 1 of the extrusion having a high toughness composition may have a L-T fracture toughness KQ of at least 36 ksi √in, or at least 38 ksi √in, or at least 40 ksi √in, or at least 42 ksi √in, or at least 44 ksi √in, or at least 45 ksi √in, or at least 47.5 ksi √in.
In certain embodiments, location 1 of the extrusion having a high toughness composition may have a T-L fracture toughness KQ of at least 30 ksi √in, or at least 31 ksi √in, or at least 33 ksi √in, or at least 35 ksi √in, at least 37 ksi √in, or at least 39 ksi √in.
In certain embodiments, location 1 of the extrusion having a high toughness composition may have a L tensile yield strength of at least 68 ksi, or at least 70 ksi, or at least 71 ksi, or at least 72 ksi, or at least 74 ksi.
In certain embodiments, location 1 of the extrusion having a high toughness composition may have a L-T tensile yield strength of at least 60 ksi, or at least 62 ksi, or at least 64 ksi, or at least 66 ksi, or at least 68 ksi.
In certain embodiments, location 1 of the extrusion having a high toughness composition may have a L elongation of at least 10 percent, or at least 12 percent, or at least 14 percent.
In certain embodiments, location 2 of the extrusion having a high toughness composition may have an off-axis three-point bend displacement d of at least 0.5 mm, or at least 0.75 mm, or at least 0.8 mm, or at least 0.9 mm, or at least 0.95 mm, or at least 0.99 mm. The increased displacement value provides enhanced resistance to failure at a location of the extrusion that may often be a point of failure.
In accordance with an embodiment of the present invention, the extrusion may be formed as a high strength composition listed as embodiment V in Table 1. By including a relatively high amount of Mn in an amount of 0.10-0.20 weight percent when extruded into the body shown in
In certain embodiments, location 1 of the extrusion having a high strength composition may achieve a L-T fracture toughness KQ of at least 32 ksi √in, or at least 34 ksi √in, or at least 36 ksi √in, or at least 38 ksi √in, or at least 40 ksi √in, or at least 41 ksi √in.
In certain embodiments, location 1 of the extrusion having a high strength composition may have a T-L fracture toughness KQ of at least 27 ksi √in, or at least 29 ksi √in, or at least 31 ksi √in, or at least 33 ksi √in, or at least 35 ksi √in.
In certain embodiments, location 1 of the extrusion having a high strength composition may have a L tensile yield strength of at least 73 ksi, or at least 74 ksi, or at least 75 ksi, or at least 76 ksi, or at least 77 ksi.
In certain embodiments, location 1 of the extrusion having a high strength composition may have a L-T tensile yield strength of at least 68 ksi, or at least 69 ksi, or at least 71 ksi, or at least 72.5 ksi.
In certain embodiments, location 1 of the extrusion having a high strength composition may have a L elongation of at least 9 percent, or at least 10.5 percent, or at least 11.5 percent.
In certain embodiments, location 2 of the extrusion having a high strength composition may have an off-axis three-point bend displacement d of at least 0.4 mm, or at least 0.45 mm, or at least 0.5 mm, or at least 0.55 mm, or at least 0.6 mm. The increased displacement value provides enhanced resistance to failure at a location of the extrusion that may often be a point of failure.
In accordance with an embodiment of the present invention, the following method may be followed using the alloy compositions of this invention, in order to obtain an extruded alloy with the desired combinations of strength, fracture toughness, corrosion resistance, and ductility. In certain embodiments, equivalent homogenization times and aging times may be calculated when multi-step homogenization and aging practices are utilized. An equivalent time at a temperature during homogenization or aging is given by the following equation:
Where t1 and t2 are times in hours, T1 and T2 are temperatures in degrees Kelvin, Q is the activation energy, and R is the universal gas constant.
In accordance with an embodiment of the present invention, the method relates to the manufacturing process for an extruded aluminum product. First, a liquid metal bath is prepared to obtain an aluminum alloy having a composition in accordance with an embodiment of the present invention. The alloy is manufactured by casting a billet, ingot, or shape from a liquid metal bath, for example, by using direct-chill casting.
The unwrought shape is homogenized such that at least one step is at a temperature between 820° F. and 870° F. such that the equivalent time at 970° F. of the step using a Q=125.6 kJ/mol and R=8.314462 JK−1mol−1 according to the equation:
is between 0.25 and 10 hours, and at least one step is at a temperature greater than 940° F. such that the total equivalent time of the entire homogenization process is between 7 and 35 hours. For example, the unwrought shape may be homogenized with a two-step homogenization process. A first step of the homogenization process may be performed at a temperature of at least 820° F., or from 820° F. to 870° F., or from 830° F. to 860° F. The first step of the homogenization process may be for a treatment time of at least 1 hour, or from 5 to 30 hours, or from 10 to 20 hours. A second step of the homogenization process may be performed at a temperature of at least 940° F., or from 930° F. to 1000° F., or from 940° F. to 980° F. The second step of the homogenization process may be for a treatment time of at least 1 hour, or from 2 to 40 hours, or from 5 to 25 hours. In certain embodiments, a two-step homogenization process may be used, but a homogenization process with any other suitable number of steps may be used, e.g., one, three, four or more steps.
In accordance with an embodiment of the present invention, the unwrought product is then hot worked into an extruded product. In an embodiment of the present invention, the F-temper extrusion may optionally be cold worked. As used herein, the term “F-temper extrusion” means an extrusion that has been fabricated using a shaping process. In certain embodiments, the extruded product is then subjected to a solution heat treatment with at least one step greater than or equal to 950° F. and then quenched. In certain embodiments, the extruded product may be kept at an ambient temperature after it is quenched for a short period of time. The extruded product may then be stretched with a permanent set of 3-9%. In accordance with an embodiment of the present invention, the extruded product may be subjected to a natural aging period to produce a T3 temper after it is stretched. The extruded product is then artificially aged by heating the extruded product to a temperature less than or equal to 315° F. for a period of time. For example, the extruded product may be artificially aged for a treatment time of at least 10 hours, or from 12 to 200 hours, or from 20 to 150 hours, or from 30 to 100 hours.
In accordance with an embodiment of the present invention, an alloy composition of this invention is provided as a billet by techniques currently known in the art for fabrication into a suitable extruded product. Billets, ingots, or shapes may be preliminary worked or shaped to provide suitable stock for subsequent working operations. Prior to the principal working operation, the billets may be subject to stress relieving and homogenization. In certain embodiments, the homogenization process may precipitate out a good network of dispersoids (ex—Al3Zr), which help control and refine the grain structure, and to homogenize the other alloyed elements (ex—Cu, Mg, etc.). In certain embodiments, in order to help precipitate out dispersoids when Zr is the main dispersoid forming element, a homogenization would contain at least one step, or alternatively a slow ramp, at a temperature of from 820° F. to 870° F., for example, from 830° F. and 860° F., such that the equivalent time of the step, or steps, or alternatively ramp, at 970° F. using a Q=125.6 kJ/mol and R−8.314462 JK−1mol−1 is between 0.25 and 10 hours. Subsequent homogenization steps should be aimed at creating a homogenized dispersion of solute in the aluminum matrix while not over-coarsening the aforementioned precipitated dispersoids if an unrecrystallized extruded structure is desired. In certain embodiments, the homogenization would contain at least one step at a temperature greater than 940° F. such that the total equivalent time of the entire homogenization is between 7 and 35 hours. In another embodiment, longer homogenization times may be used as long as the dispersoids are not over-ripened. Alternatively, if a recrystallized structure is desired, longer homogenization times can be utilized.
After homogenization, the alloy is hot worked to form an extruded product. For example, the alloy could be extruded by techniques known to those in the art. The extruded product is then solution heat treated at a temperature of from 940° F. to 1020° F., but at a temperature less than the incipient melting temperature. For example, the extruded product may be solution heat treated at a temperature greater than 960° F., or greater than 970° F. or greater than 1000° F. In certain embodiments, the extruded product is solution heat treated between 1000° F. and 1020° F. Typical furnace off-sets can be as high as ±10° F. as known to those skilled in the art.
In accordance with certain embodiments, to produce an extruded product with an improved combination of strength, toughness, and corrosion resistance, the extruded product is rapidly quenched after solution heat treatment in order to minimize, and in certain embodiments prevent, the uncontrolled precipitation of phases in the alloy. After quenching, the alloy should be plastically deformed, e.g., via stretching, at an amount great enough to ensure a uniform distribution of lithium containing metastable precipitates during the artificial aging process. For example, an extrusion should be stretched from 1 to 9 percent, or from 2 to 6 percent, or from 3 to 5 percent, if high strength is desired. In certain embodiments, to provide a higher fracture toughness, the alloy may be stretched from 1 to 3 percent as long as some compromise in strength is acceptable. In certain embodiments, the product may be stretched less than or equal to 24 hours after quenching, for example, less than 2 hours after quenching, or less than an hour after quenching. During the time period between quenching and stretching the extruded product may be kept at room temperature, e.g., may be naturally aged for a short period of time. In certain embodiments, the resulting extrusion microstructure is largely not recrystallized, e.g., the percent of recrystallized grains may be less than or equal to 25 percent. For example, the percent of recrystallized grains may be less than 20 percent, or less than 15 percent, or less than 10 percent, or less than 7.5 percent, or less than 5 percent.
After the alloy product has been worked, it may optionally be naturally aged, e.g., at room temperature, until a stable T3 temper has been established. In certain embodiments, the alloy product is allowed to naturally age for at least 48 hours. After the alloy product has been naturally aged, it may be artificially aged to provide the desired combination of strength, toughness, and corrosion resistance. In accordance with an embodiment of the present invention, the aging practice can be adjusted using an equivalent time at temperature calculation based on the desired mechanical properties and production time constraints. In certain embodiments, the alloy product should be artificially aged at temperatures equal to or less than 315° F. for 12-80 hours. In other embodiments, the alloy product should be artificially aged at temperatures between 290-310° F. for 12-80 hours. Multi-step aging treatments can also be used as long as the equivalent time at 305° F. is between 12 and 80 hours using a Q=85.27 kJ/mol. To obtain an extruded alloy product having a peak aged temper, the alloy product should be aged at a temperature of from 290-310° F. for 36-80 hours. As used herein, the term “under-aged temper” means the extruded aluminum alloy undergoes an aging treatment selected so as to achieve an under-aged product with properties that differ from those attained from a conventional temper. To obtain an under-aged product, the alloy product should be aged at a temperature of from 290-310° F. for 12-36 hours. In certain embodiments, multi-step aging treatments can be used with equivalent time at 305° F. is between 42-54 hours for a peak aged product and 14-19 hours for an under-aged product. Typical furnace off-sets can be as high as ±10° F. as known to those skilled in the art.
Alloys according to the present invention, when properly processed, should have an improved combination of strength, fracture toughness, corrosion resistance, and density without the intentional alloying addition of Ag. In certain embodiments, the alloys have a density less than 0.096 lbs/in3.
The following examples are intended to illustrate various aspects of the present invention, and are not intended to limit the scope of the invention.
In this example, several billets of Al—Cu—Li alloy wherein the composition is given in Table 2 were cast. Alloy Inv. A, Inv. B, Inv. C, and Inv. D are embodiments of alloys of the present invention. Alloys 2099A, 2099B, 2099C, and 2099D represent alloys falling within the registered Aluminum Association limits of AA2099.
The billets were homogenized according to the practices in Table 3. Billets of alloy Inv. A was homogenized according to practice H1 (835° F.—2 Hours followed by 860° F.—2 Hours followed by 950° F.—12 Hours). Billets of alloy Inv. B were homogenized according to either practice H2 (842° F.—16 Hours followed by 950° F.—10 Hours) or H3 (842° F.—16 Hours followed by 970° F.—20 Hours). Billets of alloys Inv. C and Inv. D were homogenized according to practice H3 (842° F.—16 Hours followed by 970° F.—20 Hours). Billets of alloy 2099A were homogenized according to practice H2. Billets of alloys 2099B and 2099C were homogenized according to practice H3. Billets of alloy 2099D were homogenized according to practice H1.
The homogenized billets were then subject to hot extrusion to obtain a wrought F-temper section according to
Samples taken at the end of the sections were tested to determine the static mechanical properties (Ultimate tensile strength UTS, Tensile Yield Strength TYS, and elongation at fracture “e”), fracture toughness (KQ), and corrosion resistance. The specimens used for toughness had the following dimensions: B=0.81 in and W=3 in. Exfoliation corrosion testing was done in accordance to ASTM G85—Annex 2 (i.e.—MASTMASSIS testing), and samples were rated according to the ASTM G34 (EXCO) rating system. Intergranular corrosion testing (IGC) was performed according to ASTM G110. Samples were taken from location 1 in
The average results obtained are given in Table 5, and are plotted in
As shown in
As shown in
Additionally,
The results of exfoliation corrosion testing according to ASTM G85—Annex 2. (MASTMASSIS) can be seen in Table 8. The results of the IGC testing according to ASTM G110 can be seen in
In this example, alloys from Example 1 were homogenized and hot extruded into the body shown in
Additionally, billets of alloy 2196A, whose composition falls within the registered Aluminum Association limits for AA2196 and can be seen in Table 9, were cast. The billets were then homogenized according to practice H4 (835° F.—2 Hours followed by 860° F.—6 Hours followed by 950° F.—4 Hours followed by 970° F.—22 Hours) or H5 (835° F.—2 Hours followed by 860° F.—6 Hours followed by 950° F.—4 Hours followed by 970° F.—8 Hours), which can be seen in Table 10. The billets were then hot extruded into the body shown in
Samples were taken at the end of the extruded sections from location 1 in
In this example, alloys from Examples 1 and 2 were homogenized and hot extruded into the body shown in
Samples measuring 0.787 in×0.394 in×0.079 in (20 mm×10 mm×2 mm) were then taken from location 2 as labeled in
In this example, alloys from Example 1 were homogenized and hot extruded into the body shown in
Fatigue tests were carried out on test pieces with open hole Kt=2.3 T-type specimens with a (minimum load/maximum load) ratio R=0.1 at a frequency of 30 Hz. The tests were carried out in the ambient air of the laboratory. The results are given in Table 14 and shown in
In this example, alloys from Examples 1 and 2 were homogenized and hot extruded into the body in
Tensile testing was performed according to ASTM B557—Standard Test Methods for Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products. The results can be seen in Table 16 and
In this example, artificial aging curves from the T3 temper were developed. Alloy Inv. C from Example 1 was homogenized and hot extruded in the body shown in
Samples of alloy Inv. C-H2-T3 were aged at 290° F., 305° F., and 315° F. for various times between 0 and 100 hours before being tensile tested. The results of the tensile test can be seen in Table 17 and
In this example, Alloys Inv. A, Inv. B, 2099B, and 2099C from Example 1 were homogenized and hot extruded into the body in
Samples taken at the end of the sections were tested to determine the static mechanical properties (Ultimate tensile strength UTS, Tensile Yield Strength TYS, and elongation at fracture e) and fracture toughness (KQ) at test location 1. The specimens used for toughness had the following dimensions: B=0.81 in and W=3 in. The test results can be seen in Table 19 and
Samples of Inv. B-H3-P16 and 2099B-H3-P17 also taken from the rear of the sections were then tested for fatigue crack growth rate in both a lab air environment (LAE) with a relative humidity level between 26-42% and humid air environment (HAE) with a relative humidity greater than 90%. CC(t) center crack tension specimens with a nominal width (W) of 4 in and a thickness (B)=0.2 in were used. The test results can be seen in
In this example, billets of Inv. E and 2196B, whose compositions can be seen in Table 20, were cast. It should be noted that 2196B falls within the registered limits of AA2196. Inv. E was homogenized according to H3, and 2196B was homogenized according to practice H6 (900° F.—8 Hours followed by 950° F.—24 Hours), which can be seen in Table 21. The homogenized billets were subject to hot extrusion to obtain wrought F-temper sections according to
940° F.
The samples were then tested for tensile strength according to ASTM B557. The results of these test can be seen in Table 23 and
In this example, a billet of Inv. D was homogenized according to practice H3 (842° F.—16 Hours followed 970° F.—20 Hours). The homogenized billet was then hot extruded to obtain an F-temper section according to
Additionally, alloy Inv. D-H3-P4 was sectioned for metallographic evaluation at location 1 in the L-S orientation as known to those skilled in the art. The metallographic sample was polished and etched using Barker's Reagent (4-5 mL HBF4, 200 mL H2O) using techniques known to those skilled in the art before being analyzed via optical microscopy. A micrograph of the extruded section can be seen in
For purposes of this detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/452,786, filed on Jan. 31, 2017, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62452786 | Jan 2017 | US |
