Patent Application
20210285077
The present application is directed to embodiments of a cast aluminum-copper-manganese-zirconium-based alloy and casting method embodiments using the same to provide cast parts having favorable casting properties and high ductility at room temperature for use in various industrial applications.
High-temperature cast aluminum alloys are a key material in the design of high power density automobile engines. Traditional alloys comprising aluminum, copper, manganese, and zirconium may offer an attractive material in this application, due to their strength at high temperature, favorable casting behavior, resistance to hot tearing, and good machinability; however, for such alloys, there is a trade-off between castability and ductility at low temperatures, placing practical limits on both the life cycle of the components made from such alloys and on the size and shape of the parts that can be cast. There exists, therefore, a need in the art for improved aluminum-copper-manganese-zirconium-based (or “ACMZ”) alloy embodiments that possess both good castability and room temperature ductility.
Disclosed herein are alloy composition embodiments for cast aluminum-copper-manganese-zirconium alloys. In one embodiment, the alloy comprises copper in an amount ranging from 7 wt % to 10 wt %, zirconium in an amount ranging from greater than 0.3 wt % to 0.5 wt %, manganese in an amount ranging from 0.05 wt % to 1 wt %, silicon in an amount ranging from greater than 0 wt % to 0.1 wt %, and a balance of aluminum.
Also disclosed herein are embodiments of a method comprising combining copper in an amount ranging from 7 wt % to 10 wt %, zirconium in an amount ranging from greater than 0.3 wt % to 0.5 wt %, manganese in an amount ranging from greater than 0.05 wt % to 1 wt %, silicon in an amount ranging from greater than 0 wt % to 0.1 wt %, and a balance of aluminum to form a composition, melting the composition, and solidifying the composition to form an alloy.
The foregoing and other objects and features of the present disclosure 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.
Bulk Ductility: This term refers to the ductility of the alloy bulk portion of a cast component other than a hardened surface portion of the cast component.
Cast Alloy: An alloy that is casted and is not additively manufactured.
Consists Essentially Of: The phrase “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 alloy composition or components formed from the alloy composition by additive manufacturing. Such embodiments consisting essentially of the above-mentioned components can, however, include impurities and other components that do not materially affect the physical characteristics of the alloy composition; however, those impurities and other components that do markedly alter the physical characteristics, such as the microstructural stability, strength, and/or other properties that affect performance at high temperatures, are excluded.
Ductility: This term refers to a solid material's ability to deform under tensile stress, often characterized by the material's ability to be stretched into a wire. In some embodiments, ductility may be quantified by the percent elongation in a tensile test, defined as the maximum elongation of the gage length divided by the original gage length:
The test is performed by providing a test piece of the solid material, such as a rod, marking an initial gage length, applying a tensile force to elongate the test piece until it fractures through a “neck,” and then fitting the broken parts together and measuring the final gage length (i.e., the distance between the marks made initially). In additional embodiments, ductility can be measured in terms of reduction of the cross-sectional area of the test piece at the plane of fracture, wherein the minimum final cross-sectional area is measured after fracture:
Grain Refiner: A chemical alloy additive which, when added to an alloy, results in a microstructure having a smaller average grain size than is exhibited in the absence of the grain refiner. Often, this is accomplished by altering the rates of grain nucleation and/or grain growth as the alloy is solidified.
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.
Intermetallic phase: A solid-state compound containing two or more metallic elements and exhibiting metallic bonding, defined stoichiometry and/or ordered crystal structure, optionally with one or more non-metallic elements. In some instances, an alloy may include regions of a single metal and regions of an intermetallic phase. In a quaternary alloy comprising aluminum, copper, manganese, and zirconium, the intermetallic phase may comprise both aluminum and copper, and in some cases may also comprise zirconium and/or manganese. Alloys having additional alloying elements may incorporate some portion of those elements in the intermetallic phase.
Microstructure: The fine structure of an alloy (e.g., grains, cells, dendrites, rods, laths, lamellae, precipitates) that can be visualized and examined with a microscope at a magnification of at least 25×. Microstructure can also include nanostructure, i.e., structure that can be visualized and examined with more powerful tools, such as electron microscopy, atomic force microscopy, X-ray computed tomography, etc.
TiBor: A master alloy grain refiner comprising aluminum, titanium, and boron. In a commonly-used TiBor composition, the alloy has a nominal titanium content of 5 wt %, a nominal boron content of 1 wt %, and a balance of aluminum.
Due to their light weight and favorable strength-to-weight ratios, cast aluminum alloys are increasingly sought for high-performance structural components. Of particular importance to developing automotive engines having higher power densities is obtaining cast aluminum alloys having improved mechanical properties at elevated temperature. Aluminum alloy compositions utilizing aluminum, copper, manganese, and zirconium as the main alloying elements are particularly attractive for use in automotive engines for this reason. These Al—Cu—Mn—Zr (“ACMZ”) alloys demonstrate noteworthy levels of strength at elevated temperature in addition to good castability, hot tear resistance, sand thermal conductivity, and are additionally relatively easy to machine.
The addition of copper to these ACMZ alloys has been found to further improve their castability, reducing the tendency of the alloys to hot tear during the casting process. Further additions of copper, for example at concentrations above 7.3 wt % copper, may additionally improve resistance of the alloys to mechanical creep at high temperatures, and can offer additional improvements to the thermal conductivity of the alloys. However, additional copper content also causes the formation of correspondingly greater quantities of a brittle Al—Cu intermetallic phase within the alloy. This phase accumulates at the grain boundaries between matrix grains of the alloys, as shown in
There exists, therefore, a demand for ACMZ alloy embodiments that exhibit the s capable of both the favorable castability, high temperature strength, and thermal conductivity of high-copper ACMZ alloys and of retaining high ductility at lower temperatures. Without being limited to any particular theory, it is currently believed that the addition of increased zirconium content to ACMZ alloys may disperse the Al—Cu intermetallic into particles with rounded geometries that have a smaller embrittling impact than the elongated, interconnected structures previously observed. As discussed in greater detail below, the present disclosure is directed to ACMZ alloy embodiments suitable for the casting of parts with complex geometries having elevated zirconium content and retaining high ductility at low temperatures or room temperatures. The present disclosure is also directed to methods of casting ACMZ alloy embodiments having elevated zirconium content, and to embodiments of fabricated components of the same produced by these casting method embodiments.
Disclosed herein are aluminum alloy compositions. The disclosed aluminum alloy compositions can compose a multicomponent combination of aluminum, copper, manganese, and zirconium. The Al—Cu—Mn—Zr alloy embodiments are specifically designed for favorable casting behavior, are resistant to hot tearing, have high at elevated temperatures, and retain high ductility at lower temperatures. Such alloys may be suitable, for example, for use in automobile engines, aerospace components, and the like where components of complex geometries must be cast from alloys that remain strong at high temperatures and which retain sufficient ductility at all temperatures. In some embodiments, the Al—Cu—Mn—Zr alloy can comprise Al, Cu, Mn, and Zr as the main alloying components and can further comprise other minor alloying elements and/or trace impurities.
In particular disclosed embodiments, the alloy compositions disclosed herein are made using an alloy design approach that includes incorporating elevated copper content to improve castability and reduce the susceptibility of the alloy to hot tearing. Because additional copper content in aluminum alloys may cause the formation of aluminum-copper intermetallic phases at the boundaries between the aluminum matrix grains of the alloy, some embodiments further include elemental additives to disperse and “round” the aluminum-copper intermetallic phases of aluminum alloys having elevated copper content. A rounded and dispersed geometry may, in these embodiments, provide lower stress concentrations near the aluminum-copper intermetallic phases, which in turn may contribute to improved alloy ductility at low temperatures. Without being limited to any particular theory, the addition of certain alloying elements may also cause a fraction of the aluminum-copper intermetallic phases to move away from the grain boundaries to locations within the grain bulk, further reducing stress concentration at the grain boundaries of the alloys disclosed herein.
Embodiments of the aluminum alloy compositions described herein can comprise aluminum (Al), copper (Cu), manganese (Mn), zirconium (Zr), nickel (Ni), cobalt (Co), titanium (Ti), boron (B), iron (Fe), magnesium (Mg), antimony (Sb), and any combinations thereof. In particular disclosed embodiments, the aluminum alloys consist essentially of aluminum (Al), copper (Cu), manganese (Mn), zirconium (Zr), nickel (Ni), cobalt (Co), titanium (Ti), boron (B), iron (Fe), magnesium (Mg), and antimony (Sb). In such embodiments, “consist 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, however, include impurities and other components that do not materially affect the physical characteristics of the alloy composition; however, 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. In yet additional embodiments, the aluminum alloy compositions described herein can consist of aluminum (Al), copper (Cu), manganese (Mn), zirconium (Zr), nickel (Ni), cobalt (Co), titanium (Ti), boron (B), iron (Fe), magnesium (Mg), and antimony (Sb).
ACMZ alloy embodiments disclosed herein can comprise Cu in an amount ranging from 6 wt % to 13 wt %, such as 6 wt % (or higher) to 12 wt %, 6 wt % (or higher) to 11 wt %, 6 wt % (or higher) to 10 wt %, 6 wt % (or higher) to 9 wt %, or 6 wt % (or higher) to 8 wt %, wherein such amounts include nominal and/or measured amounts. In some embodiments, Cu can be present in an amount ranging from more than 7 wt % to 13 wt %, such as 7 wt % to 12 wt %, or 7 wt % to 11 wt %, or 7 wt % to 10 wt %, or 7 wt % to 9 wt %, wherein such amounts include nominal and/or measured amounts. In particular embodiments, Cu can be present in an amount ranging from 7 wt % to 10 wt %, such as 7 wt %, 8 wt %, 9 wt %, or 10 wt %, wherein such amounts include nominal and/or measured amounts. In one representative embodiment, the amount of Cu can be 7.35 wt %, which can be a nominal and/or measured amount.
ACMZ alloy embodiments disclosed herein can also comprise Mn ranging from greater than 0 wt % to 1 wt % Mn, such as greater than 0 wt % to 1 wt %, greater than 0 wt % to 0.8 wt %, greater than 0 wt % to 0.6 wt %, greater than 0 wt % to 0.4 wt %, greater than 0 wt % to 0.2 wt %, wherein such amounts include nominal and/or measured amounts. In some embodiments, Mn can be present in an amount ranging from 0.05 wt % (or higher) to 1 wt % Mn, such as 0.05 wt % (or higher) to 0.8 wt %, 0.05 wt % (or higher) to 0.6 wt %, 0.05 wt % (or higher) to 0.4 wt %, or 0.05 wt % (or higher) to 0.2 wt %, wherein such amounts include nominal and/or measured amounts. In other embodiments, Mn can be present in amounts ranging from 0 wt % to 0.5 wt %, such as 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, or 0.5 wt %, wherein such amounts include nominal and/or measured amounts. In one representative embodiment, the amount of Mn can be 0.14 wt %, which can be a nominal and/or measured amount.
In some embodiments of the ACMZ alloys described herein, Zr can be present in an amount ranging from 0.3 wt % to 0.5 wt %, such as 0.3 wt % (or higher) to less than 0.5 wt %, 0.3 wt % (or higher) to 0.45 wt %, 0.3 wt % (or higher) to 0.4 wt %, 0.3 wt % (or higher) to 0.35 wt %, 0.3 wt % (or higher) to 0.3 wt %, or 0.3 wt % (or higher) to 0.25 wt %, wherein such amounts include nominal and/or measured amounts. In other embodiments, Zr can be present in amounts ranging from 0.3 wt % to less than 0.5 wt %, such as 0.3 wt %, 0.35 wt %, 0.4 wt %, 0.45 wt %, wherein such amounts include nominal and/or measured amounts. In one representative embodiment, the amount of Zr can be 0.4 wt %, which can be a nominal and/or measured amount. In particular embodiments, the amount of Zr is not greater than 0.45 wt %.
In some embodiments of the ACMZ alloys described in here, Si may be present in amounts ranging from greater than 0 wt % to 0.1 wt %, wherein such amounts include nominal and/or measured amounts. Without being limited to any particular theory, it is currently believed that the presence of silicon in the ACMZ alloy embodiments disclosed herein can improve the size range and distribution of precipitate phases in the solidified alloy, and can enhance or preserve the thermal stability of the precipitate phases. In one representative embodiment, the amount of Si can be 0.04 wt %, which can be a nominal and/or measured amount.
The amount of aluminum present in the above-mentioned alloys can make up the balance of the alloy composition, after Cu, Mn, Zr, Si, and any other minor elements or impurities have been accounted for.
Without being limited to any particular theory, in some embodiments, the zirconium content of the alloy may be incorporated in the aluminum-copper intermetallic phases, thereby modifying the interfacial free energy between the aluminum matrix phase and the aluminum-copper intermetallic phase, causing the aluminum-copper intermetallic phases to have a more rounded morphology. The substitutional inclusion of zirconium may additionally serve to disperse the aluminum-copper intermetallic phase, for example, by causing a fraction of the aluminum-copper intermetallic phases to form within the bulk of the aluminum matrix grains, rather than at the boundaries of the aluminum matrix grains. In these embodiments, it is to be appreciated that the dispersion of a fraction of the aluminum-copper intermetallic phases through the bulk volume of the aluminum matrix grains will reduce the fraction of the aluminum-copper intermetallic phase particles that are distributed at the grain boundaries at any constant level of total aluminum-copper intermetallic phase present in the ACMZ alloy. In some embodiments, the zirconium content in the ACMZ alloy may further cause a “rounding” of the aluminum-copper intermetallic phase particles, causing them to take on a more spherical morphology. Without being limited to any single theory of operation, it is believed that such rounded aluminum-copper intermetallic phases, when compared to flat or plate-like intermetallic phases, may have a reduced effect as stress concentrators, thereby improving the overall ductility of the alloy.
In some embodiments, minor alloying elements that can be present in the ACMZ alloys disclosed herein include nickel, cobalt, titanium, boron, iron, magnesium, antimony, or any combination thereof. In some embodiments, the amount of boron can be 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, wherein such amounts include nominal and/or measured amounts. In some embodiments, the amount of titanium present in the compositions can range from 0 wt % to 0.3 wt %, such as greater than 0 wt % to 0.3 wt %, or greater than 0 wt % to less than 0.3 wt %, or greater than 0 wt % to less than 0.2 wt %, or greater than 0 wt % to 0.15 wt %, or greater than 0 wt % to 0.1 wt %, or greater than 0 wt % to 0.05 wt %, wherein such amounts include nominal and/or measured amounts. The addition of titanium and/or boron to the alloy composition may, in some embodiments, have a grain refining effect.
The aluminum alloy compositions disclosed herein can comprise additional components, such as grain refiners, which can include master alloys. In particular disclosed embodiments, the amount of grain refiner included in the composition can be greater than, such as one order of magnitude greater than, the amount of grain refiner used in conventional compositions. In some embodiments, the amount of grain refiner included with the compositions can be selected based on a target weight percent of titanium that is to be added to the composition by introduction of the grain refiner. In such embodiments, the desired amount of additional titanium that is to be added to the composition is identified and then the amount of the master alloy to be added to a specific metal volume of the ACMZ alloy 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 composition comprising an additional amount of titanium (relative to the amount of any titanium that may be included as a minor alloying element), such as 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 can be used, such as other TiB grain refiners, TiC grain refiners, among others.
In some embodiments of the ACMZ alloys disclosed herein, the alloy may also include nickel, cobalt, magnesium, antimony, or any combination thereof. In some embodiments, the amount of any nickel or magnesium is, for each element individually less than 0.01 wt %, such as from 0 to 0.01 wt %, wherein such amounts include nominal and/or measured amounts. In some embodiments, the amount of any cobalt or antimony, for each element individually, is less than 0.1 wt %, such as from 0 wt % to 0.1 wt %, wherein such amounts include nominal and/or measured amounts. In some embodiments, iron may be present as an impurity element, but it is to be understood that iron content is generally low enough to have no substantial impact on the physical and/or chemical properties of the alloys disclosed herein.
In one specific embodiment, the ACMZ alloy can comprise 7.5 wt % copper, 0.4 wt % zirconium, 0.15 wt % manganese, less than 0.05 wt % silicon, trace or impurity amounts of iron, with the balance of the alloy made up by aluminum. Element amounts specified in this paragraph can be nominal and/or measured amounts.
In another specific embodiment, the ACMZ alloy can comprise 7.5 wt % copper, 0.1 wt % zirconium, 0.15 wt % manganese, less than 0.05 wt % silicon, trace or impurity amounts of iron, with the balance of the alloy made up by aluminum. Element amounts specified in this paragraph can be nominal and/or measured amounts.
In another specific embodiment, the ACMZ alloy can comprise 7.5 wt % copper, 0.23 wt % zirconium, 0.45 wt % manganese, 0.05 wt % silicon, and trace impurity elements with the balance of the alloy made up by aluminum. Element amounts specified in this paragraph can be nominal and/or measured amounts.
Also disclosed herein are embodiments of casting methods suitable for use with alloys according the compositions disclosed herein. The casting method embodiments described herein can involve bulk solidification methods suitable for metal alloys, such as, but not limited to, sand casting, die casting, pressurized die casting, and investment casting. Casting the ACMZ alloy compositions disclosed herein can comprise combining the desired amounts of the alloy (e.g., aluminum, copper, manganese, and zirconium, along with any minor alloying elements, such as silicon, nickel, cobalt, and antimony), melting the selected elements to form an ACMZ melt, optionally adding a grain refiner master alloy to the ACMZ melt, casting the ACMZ melt, and optionally machining the ACMZ casting to the final desired geometry.
In particular embodiments, the ACMZ alloy embodiments disclosed herein can be made according to the following method embodiments. 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 pre-heated steel mold (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. The method steps described above are scalable, and therefore are suitable for industrial scale processes.
In some embodiments of the casting methods disclosed herein, the casting process may further include the addition of one or more grain refiners to the ACMZ melt. In certain embodiments, a preferred grain refiner may be TiBor, however it is to be understood that other grain refiners suitable for refining the microstructure of aluminum alloys may also be used. In such embodiments, it may be desirable to minimize the amount of time between the addition of the grain refiner to the ACMZ alloy melt and the casting of the ACMZ alloy melt. Advantageously, the mixture can be 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.
Also disclosed herein are various embodiments of fabricated objects that can be prepared from the above-mentioned alloy compositions, according to the above-mentioned methods of alloy preparation and casting.
The microstructure of fabricated components made from the ACMZ alloys and casting processes of the present disclosure can comprise an aluminum-based matrix phase and one or more intermetallic phases. In some embodiments disclosed herein, the intermetallic phase can be an aluminum-copper intermetallic.
In some embodiments, the aluminum-based matrix phase is arranged in a cellular, crystalline structure, with the aluminum-copper intermetallic phase disposed at least in part along the boundaries between crystalline aluminum-based matrix grains. In certain embodiments, the aluminum-copper intermetallic phase can be disposed at least in part within the bulk volume of the aluminum-based matrix phase grains. In particular embodiments, the aluminum-copper intermetallic phase can be simultaneously partially disposed along the boundaries between aluminum-based matrix phase grains and partially disposed within the bulk volume of the aluminum-based matrix phase grains.
The aluminum-based matrix phase, according to the various embodiments disclosed herein may comprise a composition in which aluminum is the primary component, by weight percentage. In certain embodiments, the aluminum-based matrix phase may additionally comprise copper, manganese, zirconium, titanium, boron, silicon, nickel, cobalt, antimony, or any combination thereof. In one specific embodiment, the matrix phase may comprise aluminum, manganese, zirconium, and copper. It is to be appreciated that, at any nominal composition, the aluminum-based matrix phase may additionally comprise other elements, such as iron, at impurity-level concentrations, such as less than 0.1 wt % iron.
The aluminum-copper intermetallic phase, according to some embodiments, may comprise copper, aluminum, and one or more additional elements. In some embodiments, the aluminum-copper intermetallic phase may consist of copper and aluminum. In certain embodiments, the aluminum-copper intermetallic phase may further comprise additional alloying elements such as zirconium and manganese. Without being limited to any particular operational theory, it is currently believed that, in certain embodiments, the inclusion of zirconium in the aluminum-copper intermetallic phase causes the aluminum-copper intermetallic phase to form with a generally rounded geometry. In embodiments having aluminum-copper intermetallics with a generally rounded geometry, the aluminum-copper intermetallic particles may be spaced further apart than would be expected at lower levels of zirconium, having correspondingly less interconnectivity between the aluminum-copper intermetallic particles.
In embodiments of fabricated components prepared from compositions including one or more grain refiners, the microstructure of the fabricated component may additionally include titanium boride particles (e.g. TiB2) dispersed throughout the bulk volume of the ACMZ alloy fabricated component. Titanium boride is a ceramic material that remains chemically stable at high temperatures, and when dispersed in an alloy melt in the form of fine particles, may offer additional sites for the nucleation of metallic grains upon solidification. It currently is believed that the inclusion of grain refiners, such as TiBor, cause the formation of particles of titanium boride in the alloy while it is molten. These titanium borides have crystallographic planes with a lattice spacing similar to that of aluminum, thereby providing highly-efficient nucleation sites for the formation of aluminum grains upon the cooling of the fabricated component. In such embodiments, aluminum matrix grains may form more rapidly as the melt cools, providing for a greater total number of aluminum matrix grains, with each individual grain having a correspondingly smaller volume.
In particular embodiments using TiBor as a grain refiner, zirconium may substitutionally replace titanium in the titanium boride particles formed at elevated temperatures, forming titanium-zirconium boride. The presence of zirconium in the lattice of the titanium-zirconium boride particles may, in some embodiments, distort the lattice parameter of the boride, causing a mismatch between the lattice spacing of the titanium-zirconium boride and aluminum matrix, which in turn may reduce the efficiency of the titanium-zirconium boride as a grain refiner.
As illustrated in
Fabricated components according to the embodiments disclosed herein may be cast in any suitable range of cast geometries. In certain embodiments having 7 wt % copper to 13 wt % copper, such as 7 wt % copper, 9 wt % copper, 11 wt % copper, or 13 wt % copper, the fabricated object may exhibit a reduced propensity to hot tear or hot crack. In particular, components cast from ACMZ alloys according to the embodiments herein may demonstrate a monotonic reduction of susceptibility to hot tearing as the copper content of the alloy is increased, with some embodiments increased up to 13 wt % copper. Fabricated components having such compositions can be cast into increasingly complex geometries without the resulting components exhibiting tearing or cracking as they cool. It is to be appreciated that this offers fabricated components according to the present disclosure certain advantages, such as a reduction in the amount of machining that is required to produce a finished component that meets final geometric tolerance requirements and an increased range of useful components that may be cast according to the embodiments disclosed herein, to name a few.
Fabricated ACMZ objects made using the embodiments disclosed herein exhibit a combination of mechanical properties, thermal properties, and casting behavior that cannot be obtained using traditional ACMZ casting alloys. In particular disclosed embodiments, the fabricated ACMZ alloy objects are components used in the automotive, locomotive, aircraft, and aerospace industries. In some embodiments, the cast object is an automotive engine cylinder. Other exemplary products include, but are not limited to other automotive power train components (such as engine pistons, blocks water-cooled turbocharger manifolds, and other automotive components), aerospace components, heat exchanger components, and any other components requiring aluminum alloys that are suitable for casting complex shapes, do not lose structural integrity and/or strength at high temperatures (e.g. temperatures above 200° C., and retain high ductility at reduced temperatures).
Disclosed herein are embodiments of an alloy composition comprising: 7 wt % to 10 wt % copper; greater than 0.3 wt % to 0.5 wt % zirconium; 0.05 wt % to 1 wt % manganese; greater than 0 wt % to 0.1 wt % silicon; and aluminum.
In some embodiments the alloy is a cast alloy and has a microstructure comprising an aluminum matrix phase and an intermetallic phase comprising copper and aluminum.
In any or all of the above embodiments, the intermetallic phase has a rounded geometry.
In any or all of the above embodiments, the intermetallic phase further comprises zirconium.
In any or all of the above embodiments, the aluminum matrix phase further comprises a plurality of grain boundaries between aluminum matrix grains and the intermetallic phase is partially distributed along the plurality of grain boundaries and partially distributed within the volume of the aluminum matrix grains.
In any or all of the above embodiments, wherein the alloy further comprises one or more elements selected from nickel, cobalt, titanium, boron, iron, magnesium, or antimony.
In any or all of the above embodiments, the titanium is present in the alloy in an amount ranging from greater than 0.0 wt % to 0.3 wt % and the boron is present in the alloy in an amount ranging from greater than 0 wt % to less than 0.07 wt %.
In any or all of the above embodiments, the alloy comprises 7.5 wt % copper, greater than 0.3 to 0.4 wt % zirconium, 0.15 wt % Mn, less than 0.05 wt % silicon, and a balance of aluminum.
In any or all of the above embodiments, the alloy comprises greater than 0.3 wt % zirconium to less than 0.5 wt % zirconium.
In any or all of the above embodiments, the alloy further comprises one or more grain refiners.
In any or all of the above embodiments, the one or more grain refiners includes a TiBor master alloy, titanium boride, titanium carbide, or a combination thereof.
In any or all of the above embodiments, the alloy has a total tensile ductility of greater than 5%.
In any or all of the above embodiments, the alloy comprises 7.35 wt % copper, 0.14 wt % manganese, 0.4 wt % zirconium, less than 0.1 wt % silicon, minor impurities, and a balance of aluminum.
In any or all of the above embodiments, a component is fabricated from the alloy of claim 1.
In any or all of the above embodiments, the component is an engine component.
Also disclosed herein are embodiments of a method for making an alloy, comprising: combining 7 wt % to 10 wt % copper; greater than 0.3 to 0.5 wt % zirconium; 0.05 wt % to 1 wt % manganese; greater than 0 wt % to 0.1 wt % silicon; and aluminum to form a composition; melting the composition; and solidifying the composition to form an alloy.
In some embodiments, the solidification is accomplished by sand casting, die casting, investment casting, or pressure-assisted die casting.
In any or all of the above embodiments, the method further comprises adding one or more grain refiners to the composition.
In any or all of the above embodiments, the zirconium is present in an amount ranging from greater than 0.3 wt % to less than 0.45 wt %
In any or all of the above embodiments, the method further comprising pouring the alloy into a mold no more than 5 minutes after the one or more grain refiners have been added to the composition.
Microstructural Analysis of Low-Zr ACMZ Alloys—In this example, ACMZ alloy samples from ACMZ alloys having zirconium content lower than 0.25 wt % were prepared and analyzed for comparison purposes. Samples were prepared were analyzed using a SEM, and micrographs were prepared of the analyzed samples.
Without being limited to any particular theory, it is currently believed that the formation of long, thin, interconnected bands of the aluminum-copper intermetallic at the grain boundaries of ACMZ alloys provide stress concentrators, as well as a pathway for brittle crack failure under tensile stress. This, in turn, is believed to embrittle these alloys, particularly at low temperature or room temperature. As such, ACMZ alloys with zirconium content below 0.25 wt % typically do not comprise high copper levels without severe loss of room temperature ductility.
Energy Dispersive X-ray Spectroscopy—In this example, ACMZ alloys designated “ACMZ 2” and “ACMZ 5,” having compositions listed in Table 1 were analyzed SEM Energy Dispersive X-ray Spectroscopy (“EDS”). Specimens for EDS analysis were prepared following standard metallographic procedures.
For both alloys designated in Table 1, five measurements were taken of both the matrix grain composition and the Al—Cu intermetallic composition in weight percent, as shown in Table 2.
From the results in Table 2, an average value for the compositions, in weight percent, of the matrix and Al—Cu intermetallic phases was calculated and is presented in Table 3 and in
SEM Microscopy of ACMZ Alloys—In this example, ACMZ alloys, having compositions listed in Table 4, were analyzed using a SEM and micrographs were prepared of the analyzed samples.
Mechanical Behavior of ACMZ Alloys—In this example, the tensile properties of samples of ACMZ alloys according to the embodiments herein, having zirconium contents from 0 wt % to 0.35 wt % and copper contents from 7.3 wt % to 8.0 wt % were measured. Samples were prepared having a geometry in compliance with the ASTM E8 standard for the tensile testing of metallic materials. Samples were tested to tensile failure, and the total elongation at failure, yield strength (“YS”), and ultimate tensile strength (“UTS”) of each sample was measured.
The results of the mechanical testing are summarized in
To isolate the effect of increasing Zr content, additional testing was conducted on ACMZ alloys with nominal compositions of Al-7.5Cu-xZr-0.15Mn-0.05Si, where the numbers indicate wt % of each element, x indicates the wt % zirconium, which ranged from 0-0.4 wt %. Samples were prepared having a geometry in compliance with the ASTM E8 standard for the tensile testing of metallic materials. As-measured compositions of the tested alloys are presented in Table 5.
The results of this mechanical testing are summarized in
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the 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 application claims the benefit of the earlier filing date of U.S. Provisional Patent Application No. 62/984,803, filed on Mar. 4, 2020, which is incorporated herein by reference in its entirety.
This invention was made with government support under Contract No. DE-AC05-000R22725 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62984803 | Mar 2020 | US |
