Patent Grant
11242587
The present disclosure concerns embodiments of aluminum alloy compositions exhibiting microstructural and strength stability as well as hot tearing resistance, and methods of making and using such alloys.
The research work described here was performed under a Cooperative Research and Development Agreement (CRADA) between Oak Ridge National Laboratory (ORNL), Nemak USA Inc., and FCA US, LLC.
Cast aluminum alloys are used extensively in various industries, such as for automobile powertrain components. Among materials for these components, the aluminum alloys for engine cylinder head applications have a unique combination of physical, thermal, mechanical and castability requirements. Government regulations require increased vehicle efficiency and have pushed the maximum operating temperature of cylinder heads to approximately 250° C. It is projected that this temperature will need to increase to 300° C. to meet any future higher vehicular efficiency requirements. Conventional aluminum alloys cannot economically address the requirements of cylinder heads operating at 300° C. The widely used alloys for cylinder heads, such as 319 and 356, are not able to meet the temperature and microstructure/strength stability requirements at temperatures greater than 250° C. A need exists in the art for alloys that exhibit improved strength and microstructure stability at temperatures higher than 250° C.
Disclosed herein are embodiments of aluminum alloy compositions, comprising 8 wt % to 25 wt % copper, zirconium, manganese, aluminum, and other components. In some embodiments, the aluminum alloy compositions further comprise titanium introduced by the addition of a grain refiner to the composition. The disclosed aluminum alloy compositions exhibit improved hot tearing resistance as compared to conventional alloys and also exhibit improved microstructural and strength stability. In some embodiments, the aluminum alloy compositions can comprise strengthening precipitates having an aspect ratio≥30, such as an aspect ratio ranging from 30 to 40. In yet additional embodiments, the aluminum alloy compositions (or parts cast therefrom) can exhibit an average hot tearing index value ranging from 0.5 to 2.5. Also disclosed herein are embodiments of methods of making and using the disclosed alloys.
The foregoing and other objects, features, and advantages of the claimed invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
The following explanations of terms are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. As used herein, “comprising” means “including” and the singular forms “a” or “an” or “the” include plural references unless the context clearly dictates otherwise. The term “or” refers to a single element of stated alternative elements or a combination of two or more elements, unless the context clearly indicates otherwise.
Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and compounds similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and compounds are described below. The compounds, methods, and examples are illustrative only and not intended to be limiting, unless otherwise indicated. Other features of the disclosure are apparent from the following detailed description and the claims.
Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, percentages, temperatures, times, and so forth, as used in the specification or claims are to be understood as being modified by the term “about.” Accordingly, unless otherwise indicated, implicitly or explicitly, the numerical parameters set forth are approximations that can depend on the desired properties sought and/or limits of detection under standard test conditions/methods. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximates unless the word “about” is recited. Furthermore, not all alternatives recited herein are equivalents.
The following terms and definitions are provided:
Alloy: A metal made by melting and mixing two or more different metals. For example, an aluminum alloy is a metal made by combining aluminum and at least one other metal. In some instances, an alloy is a solid solution of metal elements.
Vickers Hardness Test: A test used to determine the hardness of an alloy, wherein hardness relates to the resistance of the alloy to indentation. Vickers hardness can be determined by measuring the permanent depth of an indentation formed by a Vickers Hardness tester, such as by measuring the depth or the area of an indentation formed in the alloy using the tester. Methods of conducting a Vickers hardness test are disclosed herein.
Hot Tearing: A type of alloy casting defect that involves forming an irreversible failure (or crack) in the cast alloy as the cast alloy cools. Hot tearing may produce cracks on the surface or inside the cast alloy. Often a main tear and numerous smaller branching tears following intergranular paths are present.
Hot Tearing (Index) Value: As used herein, this term refers to a numerical rating. Alloys were cast in the shape shown in
Representative Alloy Composition(s): This term refers to inventive alloys contemplated by the present disclosure
Solution Treating/Treatment: Heating an alloy at a suitable temperature and holding it at that temperature long enough to cause one or more alloy composition constituents to enter into a solid solution and then cooling the alloy so as to hold the alloy composition constituents in solution.
Disclosed herein are new cast aluminum alloy compositions that lead to improved elevated temperature microstructural stability and corresponding mechanical properties, as well as improved hot tearing resistance. The alloy compositions disclosed herein are based on an alloy design approach that entails incorporating coarse and yet coherent θ′ precipitates that enable improved elevated temperature microstructural stability and mechanical properties. The alloy design approach disclosed herein is contrary to the conventional wisdom and approach of incorporating fine strengthening precipitates. In conventional designs and methods, the fine strengthening precipitates lead to suitable mechanical properties at lower temperatures, but the precipitates coarsen rapidly at temperatures above 250° C. and also lose their coherency with the matrix. One unique aspect of certain embodiments of the alloys disclosed herein is the coarse strengthening precipitates, which remain stable and coherent with the matrix at high temperatures (such as up to or above 350° C.). These precipitates lead to suitable mechanical properties at lower temperature, but at elevated temperatures their mechanical and thermal properties are exceptional and much more stable than conventional alloys. Without being limited to a particular theory, it is currently believed that the elevated temperature microstructural stability of certain of the alloys compositions disclosed herein can be attributed to the selective microsegregation of alloying elements in the bulk as well as coherent/semi-coherent interfaces of θ′ precipitates. This microsegregation can “freeze” the precipitates into low energy states that renders them exceptionally stable to thermal exposure at high temperatures.
Certain embodiments of the alloy compositions disclosed herein also exhibit improved hot tearing resistance as compared to conventional alloys known in the art, such as resistance to hot tearing when the alloy cools from a melt to ambient temperature or from a hot temperature of use (e.g., 300° C.) to ambient temperature. Hot tearing susceptibility is a problem that plagues industries where intricate components and/or component designs are used, such as the automotive, aircraft, and aerospace industries. For example, many engine components must be able to resist hot tearing during production. The inventors have discovered that certain of the alloy compositions disclosed herein exhibit surprisingly superior hot tearing resistance as compared to conventional alloys. For example, some conventional alloys were found to have hot tearing values greater than 3.5 (on a scale of 0-6), whereas certain of the disclosed embodiments had hot tearing values less than or equal to 2.5. In certain embodiments, the hot tearing index value is as low as 0.5. In some embodiments, the inventors have discovered that hot tearing susceptibility can be substantially reduced and even eliminated (0%) by using alloys having the features and compositions described herein.
Disclosed herein are aluminum alloy compositions. The disclosed aluminum alloy compositions can be used to make cast aluminum alloys exhibiting microstructural stability and strength at high temperatures, such as the high temperatures associated with components used in automobiles, aerospace, and the like. Accordingly, the aluminum alloy compositions disclosed herein are able to meet the thermal, mechanical, and castability requirements in engine component manufacturing and use. Some embodiments of the disclosed aluminum alloy compositions are also suitable for other uses including, but not limited to, additive manufacturing, alloy powders, welding/fusion joining, and laser cutting/welding. In particular disclosed embodiments, the aluminum alloy compositions disclosed herein are made using an alloy design approach that includes incorporating coarse and yet coherent θ′ precipitates that enable improved elevated temperature (such as 350° C.) microstructural stability and mechanical properties. By “coarse” is meant a disk diameter>500 nm. A fine precipitate has a disk diameter<100 nm. Diameters of 100-500 nm are considered to be between coarse and fine. In particular disclosed embodiments, the cast aluminum alloys exhibit microstructural stability and strength at temperatures above 300° C., such as 325° C., 350° C., or higher. The aluminum alloy compositions and cast aluminum alloys described herein exhibit improved microstructural stability, strength, and/or castability as compared to alloys known/used in the art, such as 319, 206 alloys and RR350 alloys (Table 1 in Example 1 provides the complete compositions of some of these alloys). The alloy composition embodiments and process method embodiments disclosed herein provide alloys that exhibit properties that are surprisingly unexpected and contrary to properties observed for traditional alloys comprising fine strengthening precipitates. In some embodiments, the alloys disclosed herein comprise amounts of components that are contrary to conventional wisdom.
Embodiments of the aluminum alloy compositions described herein can comprise aluminum (Al), copper (Cu), zirconium (Zr), titanium (Ti), manganese (Mn), silicon (Si), iron (Fe), nickel (Ni), magnesium (Mg), cobalt (Co), antimony (Sb), vanadium (V), and combinations thereof. In some disclosed embodiments, the aluminum alloy compositions consist essentially of (i) aluminum (Al), copper (Cu), zirconium (Zr), titanium (Ti), manganese (Mn), and optionally, (ii) silicon (Si), iron (Fe), nickel (Ni), magnesium (Mg), cobalt (Co), antimony (Sb), and combinations thereof. In some disclosed embodiments, the aluminum alloy compositions consist essentially of aluminum (Al), copper (Cu), zirconium (Zr), manganese (Mn), silicon (Si), iron (Fe), nickel (Ni), magnesium (Mg), cobalt (Co), and antimony (Sb). “Consists essentially of” means that the alloys do not comprise, or are free of, additional components that affect one or more physical characteristics (i.e., change a numerical value of the physical characteristic by more than 5% relative to the value in the absence of the impurity or component), such as the microstructural stability and/or strength of the cast alloy composition or the hot tearing susceptibility obtained from this combination of components. Such embodiments consisting essentially of the above-mentioned components can include impurities and other components that do not materially affect the physical characteristics of the aluminum alloy composition, but those impurities and other components that do markedly alter the physical characteristics, such as the microstructural stability, strength, hot tearing, and/or other properties that affect performance at high temperatures, are excluded. For example, when the alloy includes titanium, the alloy may further include boron in an amount ranging from 0.15×the amount of titanium present to 0.4×the amount of titanium present, or carbon in an amount of from 0.2×the amount titanium present to 0.3×the amount of titanium present. In yet additional embodiments, the aluminum alloy compositions described herein can consist of (i) aluminum (Al), copper (Cu), zirconium (Zr), and manganese (Mn), and optionally (ii) silicon (Si), iron (Fe), nickel (Ni), magnesium (Mg), cobalt (Co), antimony (Sb), and combinations thereof.
As indicated above, the disclosed aluminum alloy compositions comprise manganese. In particular disclosed embodiments, manganese facilitates alloying addition, particularly in embodiments comprising low silicon amounts (e.g., where silicon is present in an amount of less than 0.1 wt %). The manganese utilized in the disclosed alloys partitions in the strengthening precipitates and also to the interfaces. Even at low amounts, manganese facilitates the segregation to the interfaces leading to desirable high temperature stability.
Use of zirconium in the disclosed alloys also can facilitate microalloying, i.e., the addition of another element in small amounts, such as 0.5 wt % or less. In particular disclosed embodiments, using low amounts of zirconium (e.g., 0.05-0.15 wt %) in combination with manganese can stabilize the interface to higher temperature. Without being limited to a particular theory of operation, it is currently believed that combining the manganese and zirconium can lower the interfacial energy synergistically and also act as double diffusion barriers on the precipitate-matrix interfaces. In some embodiments, zirconium atoms are located on the matrix side and manganese atoms are located on the precipitate side of this interface.
When titanium is used in the disclosed alloys, it can be located at sites similar to the zirconium, but typically is less effective as a high temperature stabilizer on its own (that is, when not used in combination with zirconium). The effectiveness of the titanium can be improved by adding additional titanium in conjunction with boron, such as by adding a grain refiner to the alloy composition. In some embodiments, using a grain refiner comprising titanium and boron can result in the addition of up to 0.07 wt % boron, such as ≤0.067 wt % boron, ≤0.04 wt % boron, ≤0.033 wt % boron, or ≤0.02 wt % boron. The amount of titanium added from introducing the grain refiner is discussed below. In some embodiments, the grain refiner is the only source of titanium in the alloy. The presence of a grain refiner can be detected by analyzing the alloy for additional components of the grain refiner, e.g., boron.
The amount of each component that can be used in certain embodiments of the disclosed aluminum alloy compositions is described. In some embodiments, the amount of copper present in the alloys can range from 8 wt % to 25 wt % or >8 wt % to 25 wt %, such as >8 wt % to 22 wt %, >8 wt % to 20 wt %, >8 wt % to 18 wt %, 8 wt % to 15 wt %, >8 wt % to 15 wt %, 8.5 wt % to 25 wt %, 8.5 wt % to 20 wt %, 8.5 wt % to 18 wt %, 8.5 wt % to 15 wt %, 9 wt % to 25 wt %, 9 wt % to 20 wt %, 9 wt % to 18 wt %, 9 wt % to 15 wt %. In particular disclosed embodiments, the amount of copper present in the aluminum alloy composition can be selected from 8 wt %, 8.5 wt %, 9 wt %, 10 wt %, 11 wt %, 12 wt %, 13 wt %, 14 wt %, 15 wt %, 16 wt %, 17 wt %, 18 wt %, 19 wt %, 20 wt %, 21 wt %, 22, wt %, 23 wt %, 24 wt %, or 25 wt %. In some embodiments, when the amount of copper is 8 wt % or 8.0-8.4 wt %, the alloy includes from 0 wt % to less than 0.05 wt % titanium, such as from 0 wt % to less than 0.045 wt %, from 0 wt % to less than 0.04 wt %, or from 0 wt % to less than 0.03 wt % titanium.
In some embodiments, the amount of zirconium present in the alloys can range from 0.05 wt % to 0.3 wt %, such as 0.05 wt % to 0.25 wt %, 0.05 wt % to 0.2 wt %, or 0.05 wt % to 0.15 wt %. In particular disclosed embodiments, the amount of zirconium present in the alloys can be selected from 0.05 wt %, less than 0.07 wt %, 0.1 wt %, 0.15 wt %, 0.2 wt %, 0.25 wt %, or 0.3 wt %.
In some embodiments, the amount of titanium present in the alloys can range from 0 wt % to 0.3 wt %, such as greater than 0 wt % to 0.3 wt %, 0 wt % to 0.2 wt %, 0.02 wt % to 0.2 wt %, 0 wt % to less than 0.2 wt %, 0 wt % to 0.15 wt %, 0 wt % to 0.1 wt %, 0 wt % to 0.05 wt % 0 wt % to 0.045 wt %, 0 wt % to 0.04 wt %, 0 wt % to 0.03 wt %, 0 wt % to 0.02 wt %. In particular disclosed embodiments, the amount of titanium present in the alloys can be selected from 0.2 wt %, 0.15 wt %, 0.1 wt %, ≤0.05 wt %, ≤0.045 wt %, ≤0.04 wt %, ≤0.03 wt %, ≤0.02 wt %, ≤0.01 wt %, or ≤0 wt %.
Elemental titanium may be added to the alloy and/or titanium may be added by a grain refiner. In one embodiment, titanium is added to the alloy. In one embodiment, titanium is added to the alloy, and a grain refiner provides the alloy with additional titanium. In an independent embodiment, the grain refiner is the only source of titanium in the alloy. In still another independent embodiment, the alloy is devoid of, essentially devoid of (i.e., contains ≤0.03 wt %), or substantially devoid of (≤0.045 wt %) titanium. In certain embodiments, the amount of titanium is from greater than 0 wt % to 0.2 wt %, and the alloy further comprises (i) boron in an amount of from 0.15×the amount of titanium present to 0.4×the amount of titanium present, or (ii) carbon in an amount of from 0.2×the amount of titanium present to 0.3×the amount of titanium present. In particular embodiments, the alloy further comprises boron in an amount of from 0.2×the amount of titanium present to 0.33×the amount of titanium present, or carbon in an amount of 0.25×the amount of titanium present. The source of titanium (e.g., elemental titanium or a grain refiner) can be determined by performing an elemental analysis of the alloy to determine whether other components of a grainer refiner, such as boron or carbon, are present. Presence of boron or carbon, particularly in an amount corresponding to a ratio of titanium to boron or carbon in a grain refiner, provides evidence that a grain refiner was added to the alloy.
In some embodiments, the amount of manganese present in the alloys can range from 0.05 wt % to 1 wt %, such as 0.1 wt % to 0.75 wt %, 0.2 wt % to 0.5 wt %, 0.2 wt % to 0.48 wt %, 0.3 wt % to 0.4 wt %, 0.1 wt % to 0.3 wt %, or 0.05 wt % to less than 0.2 wt %. In particular disclosed embodiments, the amount of manganese present in the alloys can be selected from 0.05 wt %, 0.1 wt %, less than 0.2 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.45 wt % 0.5 wt %, or 0.75 wt %.
In some embodiments, the amount of silicon present in the alloys can range from 0 wt % to 0.2 wt %, such as greater than 0 wt % to less than 0.2 wt %, ≤0.15 wt %, greater than 0 wt % to 0.15 wt %, ≤0.1 wt %, 0.01 wt % to 0.1 wt %, 0.01 wt % to 0.05 wt %, 0.01 wt % to 0.05 wt %, 0.01 wt % to 0.04 wt %, 0.01 wt % to 0.03 wt %, 0.01 wt % to 0.02 wt %. In particular disclosed embodiments, the amount of silicon present in the alloys can be selected from 0 wt %, 0.01 wt %, 0.02 wt %, 0.03 wt %, 0.04 wt %, 0.05 wt %, 0.06 wt %, 0.07 wt %, 0.08 wt %, 0.09 wt %, or 0.1 wt %.
In some embodiments, the amount of iron present in the alloys can range from 0 wt % to 0.5 wt %, such as greater than 0 wt % to less than 0.5 wt %, greater than 0 wt % to less than 0.2 wt %, greater than 0 wt % to 0.15 wt %, greater than 0 wt % to 0.1 wt %, greater than 0 wt % to 0.05 wt %, or 0.05 wt % to ≤0.2 wt %. In particular disclosed embodiments, the amount of iron present in the alloys can be selected from 0.2 wt %, 0.15 wt %, 0.1 wt %, or 0.05 wt %.
In some embodiments, the amount of nickel present in the alloys can range from 0 wt % to 0.01 wt %, such as greater than 0 wt % to less than 0.01 wt %, greater than 0 wt % to 0.0075 wt %, greater than 0 wt % to 0.005 wt %, greater than 0 wt % to 0.0025 wt %, or 0.0025 wt % to ≤0.01 wt %. In particular disclosed embodiments, the amount of nickel present in the alloys can be selected from 0 wt %, 0.0025 wt %, 0.005 wt %, 0.0075 wt %, or 0.01 wt %.
In some embodiments, the amount of magnesium present in the alloys can range from 0 wt % to 0.01 wt %, such as greater than 0 wt % to less than 0.01 wt %, greater than 0 wt % to 0.0075 wt %, greater than 0 wt % to 0.005 wt %, greater than 0 wt % to 0.0025 wt %, or 0.0025 wt % to ≤0.01 wt %. In particular disclosed embodiments, the amount of magnesium present in the alloys can be selected from 0 wt %, 0.0025 wt %, 0.005 wt %, 0.0075 wt %, or 0.01 wt %.
In some embodiments, the amount of cobalt present in the alloys can range from 0 wt % to 0.1 wt %, such as greater than 0 wt % to less than 0.1 wt %, greater than 0 wt % to 0.08 wt %, 0.01 wt % to 0.07 wt %, 0.01 wt % to 0.06 wt %, 0.01 wt % to 0.05 wt %, 0.01 wt % to 0.04 wt %, 0.01 wt % to 0.03 wt %, or 0.01 wt % to 0.02 wt %. In particular disclosed embodiments, the amount of cobalt present in the alloys can be selected from 0 wt %, 0.01 wt %, 0.02 wt %, 0.03 wt %, 0.04 wt %, 0.05 wt %, 0.06 wt %, 0.07 wt %, 0.08 wt %, 0.09 wt %, or 0.1 wt %.
In some embodiments, the amount of antimony present in the alloys can range from 0 wt % to 0.1 wt %, such as greater than 0 wt % to less than 0.1 wt %, greater than 0 wt % to 0.08 wt %, 0.01 wt % to 0.07 wt %, 0.01 wt % to 0.06 wt %, 0.01 wt % to 0.05 wt %, 0.01 wt % to 0.04 wt %, 0.01 wt % to 0.03 wt %, or 0.01 wt % to 0.02 wt %. In particular disclosed embodiments, the amount of antimony present in the alloys can be selected from 0 wt %, 0.01 wt %, 0.02 wt %, 0.03 wt %, 0.04 wt %, 0.05 wt %, 0.06 wt %, 0.07 wt %, 0.08 wt %, 0.09 wt %, or 0.1 wt %.
The amount of aluminum present in the alloys is the balance (or remainder) wt % needed to achieve 100 wt % with other components, and in such embodiments, there may be unavoidable impurities present in the alloy, wherein the total content of impurities amounts to no more than 0.2 wt %, such as 0 to 0.15 wt %, 0 to 0.1 wt %, or 0 to 0.5 wt %. In particular disclosed embodiments, the amount of aluminum present in the alloy can range from 72 wt % to 92 wt %, such as 73 wt % to 92 wt %, 74 wt % to 92 wt %, 74 wt % to 91.5 wt %, 75 wt % to 92 wt %, 75 wt % to 91.5 wt %, 80 wt % to 92 wt %, 80 wt % to 91.5 wt %, 85 wt % to 92 wt %, 85 wt % to 91.5 wt %, 85 wt % to 91 wt % or 85 wt % to 90 wt %.
In particular disclosed embodiments, the amount of manganese present in the aluminum alloy compositions is greater than that of the amount of iron present, the amount of zirconium present is greater than that of the amount of titanium, or both such conditions apply. In yet additional embodiments, the amount of manganese present in the aluminum alloy compositions is greater than the amount of silicon present, with particular disclosed embodiments having manganese present in an amount greater than 3 times the amount of silicon present. In particular disclosed embodiments, the amount of silicon included in the alloy is kept to a minimum, with certain embodiments having amounts of silicon lower than 0.2 wt %, such as less than 0.1 wt %, or less than 0.08 wt % or less than 0.05 wt %. The amount of silicon present in the alloys is typically minimized so as to avoid poisoning the precipitate-matrix interface. Higher amounts lead to the formation of the thermodynamically stable phase that can coarsen rapidly leading to a rapid loss in mechanical properties. Si content desirably is <0.1 wt % for best results. In additional embodiments, the amount of magnesium present in the alloys is kept to a minimum. Magnesium, particularly in combination with silicon, is a fast diffusing element that can rapidly partition to the strengthening precipitate and not allow the effective alloying elements, such as manganese and zirconium, to invoke temperature stabilization. Other elements that can constitute impurities include, but are not limited to, iron, cobalt, nickel, and antimony. Iron typically is maintained below a level of 0.2 wt % to avoid forming intermetallics, which can have a detrimental effect on the hot tearing resistance of the disclosed alloys.
Particular disclosed aluminum alloy compositions comprise 8 wt % to 25 wt % copper, 0.1 wt % to 0.3 wt % zirconium, less than 0.05 wt % titanium (before addition of a grain refiner), 0.1 wt % to 1 wt % manganese, and the remainder being aluminum. Such embodiments can further comprise up to 0.1 wt % silicon, up to 0.2 wt % iron, up to 0.01 wt % nickel, up to 0.01 wt % magnesium, up to 0.1 wt % cobalt, up to 0.1 wt % antimony, or any combination thereof.
In some embodiments, the amount of each component present in the alloy can vary based on the portion of the casting analyzed with, for example, inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry. In some embodiments, the alloy casting can comprise an amount of each component matching those described above. In yet additional embodiments, different portions (e.g., an outer surface of a casting, an inner portion of the casting, and the like) of a casting can comprise an amount of each component that substantially matches the amounts described above, wherein “substantially matches” means that the amount of the particular component within the alloy ranges from 80% to 110% of the amounts disclosed herein, such as 85% to 105%, or 90% to 99%, or 90% to 95%.
The aluminum alloy compositions disclosed herein can comprise grain refiners. In particular disclosed embodiments, the amount of grain refiner included in the alloy can be greater than, such as one order of magnitude greater than, the amount of grain refiner used in conventional alloys. In some embodiments, the amount of grain refiner included with the alloys can be selected based on a target weight percent of titanium that is to be added to the alloy by introduction of the grain refiner. In such embodiments, the desired amount of additional titanium that is to be added to the alloy is identified and then the amount of the master alloy to be added (typically in kgs) to a specific metal volume to increase the titanium amount by the additional amount is calculated. In particular disclosed embodiments, the amount of the grain refiner that is added can vary with the type of master alloy used.
As indicated above, the grain refiner can contribute to the amount of titanium present in the alloy compositions. For example, using a grain refiner can result in the alloy comprising an additional amount of titanium, such as from greater than zero to 0.2 wt % additional Ti, from 0.02 wt % to 0.2 wt % additional Ti, or from 0.02 wt % to 0.15 wt % additional Ti, or from 0.02 wt % to 0.1 wt % additional Ti. In particular disclosed embodiments, the amount of additional Ti introduced by adding a grain refiner can be 0.02 wt %, 0.1 wt %, or 0.2 wt %. Suitable grain refiners include, but are not limited to grain refiners that facilitate nucleation of new grains of aluminum. Some grain refiners can include, but are not limited to, grain refiners comprising aluminum, titanium, boron, and combinations thereof, which can include master alloys. In particular disclosed embodiments, the grain refiner can be a TiBor master alloy grain refiner, which is a grain refiner comprising a combination of aluminum, titanium, and boron. The grain refiner can comprise titanium in an amount ranging from 2 wt % to 6 wt %, such as 3 wt % to 6 wt %, or 3 wt % to 5 wt %; boron in an amount ranging from 0.5 wt % to 2 wt %, such as 0.5 wt % to 1 wt %, or 0.75 wt % to 1 wt %; and aluminum making up the remainder wt %; and any combination thereof. In exemplary embodiments, the TiBor grain refiner comprises 94 wt % aluminum, 5 wt % titanium, and 1 wt % boron, or 96 wt % aluminum, 3 wt % titanium, and 1 wt % boron. Other grain refiners known in the art can be used in combination with the alloy compositions disclosed herein, such as TiB or TiC, among others. In particular disclosed embodiments, grain refiners can be used to improve the hot tear resistance of the cast aluminum alloy compositions. In particular disclosed embodiments, the hot tear resistance of the cast aluminum alloy compositions can be further improved by using the grain refiners in combination with alloy composition embodiments comprising 8 wt % to 25 wt % copper, >8 wt % to 25 wt % copper, 8.5 wt % to 25 wt % copper, 9 wt % to 25 wt % copper, 8 wt % to 15 wt % copper, >8 wt % to 15 wt % copper, 8.5 wt % to 15 wt % copper, or 9 wt % to 15 wt % copper. Conventionally, when an alloy is referred to as including a particular percentage of grain refiner, the percentage refers to the weight percent of titanium added by the grain refiner. For example, an alloy containing “0.1 wt % TiBor” contains an additional 0.1 wt % titanium provided by TiBor addition.
In one embodiment, the aluminum alloy composition comprises, consists essentially of, or consists of >8 wt % to 25 wt % copper, 0.4-0.5 wt % manganese, 0.1-0.3 wt % zirconium, 0.1 wt % titanium added via a grain refiner, less than 0.2 wt % silicon, less than 0.2 wt % iron, less than 0.01 wt % nickel, less than 0.01 wt % magnesium, less than 0.1 wt % cobalt, less than 0.1 wt % antimony, with aluminum making up the balance, along with 0.02-0.033 wt % boron and/or 0.025 wt % carbon from the grain refiner, and 0 wt % to 0.2 wt % unavoidable impurities. In an independent embodiment, the aluminum alloy compositions can comprise, consist essentially of, or consist of 8-15 wt % copper, 0.4-0.5 wt % manganese, 0.15-0.25 wt % zirconium, less than 0.05 wt % titanium, ≤0.1 wt % silicon, less than 0.2 wt % iron, less than 0.01 wt % nickel, less than 0.01 wt % magnesium, less than 0.1 wt % cobalt, less than 0.1 wt % antimony, with aluminum making up the balance, along with 0 wt % to 0.2 wt % unavoidable impurities. In another independent embodiment, the aluminum alloy compositions can comprise, consist essentially of or consist of 8-25 wt % copper, 0.05-1 wt % manganese, 0.05-0.3 wt % zirconium, 0-0.045 wt % titanium, ≤0.1 wt % silicon, 0-0.1 wt % iron, 0-0.01 wt % nickel, 0-0.01 wt % magnesium, 0-0.1 wt % cobalt, 0-0.1 wt % antimony, with aluminum making up the balance, along with 0 wt % to 0.2 wt % unavoidable impurities. In another independent embodiment, the aluminum alloy compositions can comprise, consist essentially of, or consist of 8-15 wt % copper, 0.45 wt % manganese, 0.2 wt % zirconium, ≤0.03 wt % titanium, less than 0.2 wt % silicon, less than 0.2 wt % iron, less than 0.01 wt % nickel, less than 0.01 wt % magnesium, less than 0.1 wt % cobalt, less than 0.1 wt % antimony, with aluminum making up the balance, along with 0 wt % to 0.2 wt % unavoidable impurities. In another independent embodiment, the aluminum alloy compositions can comprise, consist essentially of, or consist of 8.5-15 wt % copper, 0.45 wt % manganese, 0.2 wt % zirconium, 0.02-0.2 wt % titanium, less than 0.2 wt % silicon, less than 0.2 wt % iron, less than 0.01 wt % nickel, less than 0.01 wt % magnesium, less than 0.1 wt % cobalt, less than 0.1 wt % antimony, with aluminum making up the balance, along with 0.004 wt % to 0.067 wt % boron or 0.005 wt % to 0.05 wt % carbon, and 0 wt % to 0.2 wt % unavoidable impurities. In another independent embodiment, the aluminum alloy compositions can comprise, consist essentially of, or consist of 8.5-15 wt % copper, 0.45 wt % manganese, 0.2 wt % zirconium, 0.1 wt % titanium, less than 0.2 wt % silicon, less than 0.2 wt % iron, less than 0.01 wt % nickel, less than 0.01 wt % magnesium, less than 0.1 wt % cobalt, less than 0.1 wt % antimony, with aluminum making up the balance, along with 0.02 wt % to 0.033 wt % boron or 0.025 wt % carbon, and 0 wt % to 0.2 wt % unavoidable impurities. In another independent embodiment, the aluminum alloy compositions can comprise, consist essentially of, or consist of 9-15 wt % copper, 0.45 wt % manganese, 0.2 wt % zirconium, 0.02-0.2 wt % titanium, less than 0.2 wt % silicon, less than 0.2 wt % iron, less than 0.01 wt % nickel, less than 0.01 wt % magnesium, less than 0.1 wt % cobalt, less than 0.1 wt % antimony, with aluminum making up the balance, along with 0.004 wt % to 0.067 wt % boron or 0.005 wt % to 0.05 wt % carbon, and 0 wt % to 0.2 wt % unavoidable impurities. In another independent embodiment, the aluminum alloy compositions can comprise, consist essentially of, or consist of 9-15 wt % copper, 0.45 wt % manganese, 0.2 wt % zirconium, 0.1 wt % titanium, less than 0.2 wt % silicon, less than 0.2 wt % iron, less than 0.01 wt % nickel, less than 0.01 wt % magnesium, less than 0.1 wt % cobalt, less than 0.1 wt % antimony, with aluminum making up the balance, along with 0.02 wt % to 0.033 wt % boron or 0.025 wt % carbon, and 0 wt % to 0.2 wt % unavoidable impurities.
In contrast to conventional alloy compositions, which incorporate fine strengthening precipitates, the aluminum alloy compositions described herein comprise coarse strengthening precipitates that remain stable and coherent with the matrix at high temperatures, such as temperatures above 250° C. (e.g., 350° C.). Unlike fine strengthening precipitate alloy compositions that exhibit good mechanical properties at lower temperature but that coarsen rapidly at temperatures above 250° C. and lose their coherency with the matrix, the disclosed alloy compositions are able to perform and remain stable at temperatures well above 250° C. Without being limited to a single theory of operation, it is currently believed that the elevated temperature microstructural stability of the disclosed aluminum alloys is attributable to the selective microsegregation of alloying elements in the bulk as well as coherent/semi-coherent interfaces of θ′ precipitates. It is also currently believed that this microsegregation can “freeze” the precipitates into low energy states that renders them exceptionally stable to thermal exposure at high temperatures, such as temperatures between 250° C. to 350° C., or higher. High resolution transmission electron microscopic (HRTEM) images of the coarse e′ type precipitate in a representative alloy that is relatively coherent with the aluminum matrix (both along precipitate rims and faces) are shown in
The exceptional high temperature stability of a representative microstructure is illustrated in
As can be seen in
Aluminum alloy compositions disclosed herein also exhibit improved hot tearing susceptibility as compared to other aluminum alloy compositions, such as 206-type alloys, 319 alloys, 356 alloys, and RR350 alloys. In particular disclosed embodiments, the hot tearing susceptibility of an alloy composition, as described herein, can be measured by making a plurality of castings of an aluminum alloy composition in a particular shape, such as that illustrated in
The aluminum alloy compositions described herein can be made according to the following methods. In particular disclosed embodiments, the aluminum alloy compositions described herein can be made by combining cast aluminum alloy precursors with pre-melted alloys that provide high melting point elements. The cast aluminum alloy precursors are melted inside a reaction vessel (e.g., graphite crucible or large-scale vessel). The pre-melted alloys are prepared by arc-melting in advance. The reaction vessel is retained inside a box furnace at, for example, 775° C., with Ar cover gas for a suitable period of time (e.g., 30 minutes or longer). The melted Al alloys are then poured into a steel mold pre-heated, e.g., pre-heated at 300° C. Prior to the pouring, the molten metal inside the crucible is stirred by using a graphite rod pre-heated at 300° C., to verify that all elements or pre-melted alloys were fully dissolved into the liquid. Heat treatments such as solution annealing, aging, and pre-conditioning can be applied to the cast Al alloys inside a box furnace in laboratory air. The temperature can be monitored by a thermo-couple attached to the material surface. Vickers hardness of the heat-treated materials can be measured on the cross-sectional surface at 5-kg load. The average hardness data obtained from 10 indents can be used as a representative of each annealing condition. The method steps described above are scalable and therefore are suitable for industrial scale methods.
In some embodiments, the methods can include heating the compositional components under a solution heat treatment procedure at a temperature ranging from 525° C. to 540° C. After the solution heat treatment, the alloy can be aged at a temperature ranging from 150° C. to 300° C., such as from 150° C. to less than 210° C. ° C., 150° C. to 190° C., 210° C. to 300° C., or 225° C. to 300° C. In some embodiments, a lower aging treatment temperature can be used to improve low temperature strength (that is, at temperatures lower than 200° C. but greater than 100° C.) of the cast alloy, whereas higher aging treatment temperatures can be used to improve high temperature stability of the cast alloy by preventing thermal growth of precipitates during service.
In some embodiments, a grain refiner (e.g., TiBor, TiB, or TiC) is added to the alloy prior to casting to provide a mixture of the alloy and the grain refiner. Advantageously, the mixture is poured into a pre-heated mold substantially immediately (e.g., less than 10 minutes) after adding the grain refiner. For example, the mixture may be poured into the pre-heated mold within 1-5 minutes of adding the grain refiner, such as within 5 minutes, within 4 minutes, within 3 minutes, within 2 minutes, or within 1 minute of adding the grain refiner.
The aluminum alloy compositions disclosed herein can be used in applications using cast aluminum compositions. The aluminum alloy compositions are suitable for use in myriad components requiring cast aluminum alloy structures, with exemplary embodiments including, but not being limited to, automotive powertrain components (such as engine cylinder heads, blocks, pistons, water cooled turbocharger manifolds, and other automotive components), aerospace components, heat exchanger components, or other components requiring stable aluminum-containing compounds at high temperatures. In particular disclosed embodiments, the disclosed aluminum alloy compositions can be used to make cylinder heads or engine blocks for internal combustion engines and are particularly useful for components having ornamental shapes or details.
Some embodiments of the disclosed aluminum alloy compositions do not include a grain refiner. Such embodiments may be suitable for casting as described above, but also are suitable in other forms and/or for other uses, such as additive manufacturing, alloy powders, welding/fusion joining, and laser cutting/welding.
In some examples, cast Al alloys with nominal weight of 270 g were melted inside a graphite crucible by using pure element feedstock together with pre-melted alloys for high melting point elements. The pre-melted alloys were prepared by arc-melting in advance. The graphite crucible was kept inside a box furnace at 775° C. with Ar cover gas for more than 30 minutes. The melted Al alloys were then poured into a steel mold pre-heated at 300° C. with a size of 25×25×150 mm. Prior to the pouring, the molten metal inside the crucible was stirred by using a graphite rod pre-heated at 300° C., to verify that all elements or pre-melted alloys were fully dissolved into the liquid. Heat treatments such as solution annealing, aging, and pre-conditioning were applied to the cast Al alloys inside a box furnace in laboratory air. The temperature was monitored by a thermo-couple attached to the material surface. Vickers hardness of the heat-treated materials was measured on the cross-sectional surface at 5-kg load with a 10-second loading time. The average hardness data obtained from 10 indents was used as a representative of each annealing condition.
In a particular disclosed embodiments, a quantitative comparison of the hot tearing susceptibility of various aluminum alloy compositions disclosed herein and other aluminum alloy compositions was conducted. In some embodiments, several castings were made in the shape shown in
A comparison of the compositional components of three baseline alloys and six inventive alloys is provided by Table 1. Hot-tearing data/results produced by 206, 319, and RR350 alloys are provided by Tables 2-4.
Additional alloys having an approximate composition of Al-xCu-0.45Mn-0.2Zr-0.1Fe-0.1Si were prepared where the numbers indicate wt % of each element, x indicates the wt % copper, which ranged from 3-43 wt %. The alloys were low in Fe and Si, approximately 0.1 wt % of each. The grain refiner content varied from 0-0.2 wt % Ti via a standard TiBor grain refinement master alloy. Each alloy was evaluated for experimental hot tear index as described above. A lower hot tear index indicates better hot tear resistance. The best hot-cracking resistance was obtained at 0.1 wt % Ti via TiBor. The results are presented in Tables 5-12 and
As can be seen from Tables 5-12 and
Atomic level imaging and characterization of a prototypical type B alloy (Al5CuNi) alloy is summarized in
Precipitation hardening in aluminum alloys is well known to proceed through a series of transition phases (GP I→θ″→θ′→θ) to form the equilibrium Al2Cu (θ) phase. The least thermodynamically stable phases (GP I and θ″) have the lowest nucleation barrier due to their coherent interfaces with matrix and, thus, lead to the finest distributions (
The thermodynamic stability of the θ′ phase in type A and type B alloys is comparable according to predictions shown in
dt3−do3=κt, where κ=DγscXe (1)
which assumes that volume diffusion is the rate controlling step and dt and do are mean diameters of particles at time, t and t=0, D is the diffusion coefficient, γsc is interfacial energy of the semi-coherent interface and Xe is the equilibrium solubility of very large particles. The strengthening θ′ precipitate has two interfacial energies (
Without being limited to a particular theory of operation, it is currently believed that a smaller diffusion coefficient and a reduced interfacial energy can lead to improved coarsening resistance and thus it is these factors that can lead to the extreme coarsening resistance of type B alloys. Precipitate growth and coarsening on the coherent surfaces is through a ledge mechanism in this alloy and a key characteristic of type B alloys is a “freezing” of the coarsening of the precipitates over an extended temperature range. The lower energy for the semi-coherent interface in type B alloys is evidenced by facets on the precipitate in
In some embodiments, it is noted that in terms of their ability to stabilize the θ′ precipitate up to a certain temperature, the alloying elements and combinations thereof can be selected using a hierarchy scheme, which is determined by the temperature at which sustained exposure leads to a rapid drop in hardness such that Al—Cu (<200° C.)<Si addition ˜Zr addition (200-250° C.)<Mn addition (250-300° C.)<Mn+Zr addition (>350° C.). Such results further indicate that a continuum may exist in the ability of desirable elements and their combinations to stabilize the metastable θ′ to a specific temperature. This continuum creates the possibility that newer alloys can be designed that will stabilize the metastable θ′ precipitate all the way up to the θ solvus temperature (˜420° C. for Al-5Cu in
In view of the many possible embodiments to which the principles of the present disclosure may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the disclosure and should not be taken as limiting the scope of the claimed invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.
This invention was made with government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
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