US20230340646A1

US20230340646A1 - Multipurpose aluminum alloy composition

Info

Publication number: US20230340646A1
Application number: US17/853,410
Authority: US
Inventors: Henry Zhan; Zhou Wang; Jianfeng Wang
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2022-04-22
Filing date: 2022-06-29
Publication date: 2023-10-26
Also published as: CN116970846A; DE102022115004A1

Abstract

An aluminum alloy and shaped aluminum alloy parts cast therefrom. The aluminum alloy including, by mass, ≥about 6.5% to ≤about 8% silicon, ≥about 0.1% to ≤about 0.35% magnesium, ≥about 0.2% to ≤about 0.25% iron, ≥about 0.05% to ≤about 0.15% manganese, and ≥about 0.1% to ≤about 0.2% chromium. The mass percentage of iron (Fe%), the mass percentage of manganese (Mn %), and the mass percentage of chromium (Cr %) in the aluminum alloy satisfy the relationships: (i) [Mn %+(a×Cr %)]/Fe %>1, and (ii) Fe %+(b×Mn %)+(c×Cr %)>0.6%, where about 1.3≤a≤about 1.7, about 1.2≤b≤about 1.7, and about 2.5≤c≤about 2.9.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit and priority of CN202210427927.8, filed Apr. 22, 2022. The entire disclosure of the above application is incorporated herein by reference.

INTRODUCTION

This section provides background information related to the present disclosure which is not necessarily prior art.
The present disclosure generally relates to aluminum alloys and, more particularly, to aluminum alloys for use in casting shaped aluminum alloy parts.
Aluminum alloys are used in the manufacture of consumer products and component parts and may be formed into desired shapes via a variety of methods, including via die casting and permanent mold casting. In traditional casting processes, molten metal is introduced into a mold cavity and allowed to cool and solidify prior to removal of the cast part therefrom. A lubricant may be sprayed onto an interior surface of the mold cavity prior to casting, for example, to help control the temperature of the mold and to assist in removal of the cast part from the mold. In some casting processes (e.g., high pressure die casting processes), molten metal is forced into the mold cavity under high gauge pressure (e.g., at pressures of about 1,500 psi to about 25,400 psi), which may facilitate fast filling of the mold cavity and may allow for high volume production of parts having relatively thin walls (e.g., less than about 5 millimeters). In other casting processes, mold metal may be introduced into the mold cavity by gravity, by application of a relatively low gauge pressure (e.g., about 3 psi to about 50 psi), or under vacuum, which may facilitate production of relatively thick-walled (e.g., greater than about 5 millimeters) cast parts having relatively low porosity. Examples of these relatively low-pressure casting processes include permanent mold casting (e.g., low pressure die casting, counter pressure casting, and gravity casting) and sand casting.
Molds used for casting aluminum alloy parts are oftentimes made of steel and a casting defect known as soldering may occur during the casting process when molten aluminum sticks or solders to the interior surface of the mold cavity and remains in the cavity after removal of the cast part from the mold. To avoid soldering defects, the aluminum alloys may be formulated to include relatively high amounts of iron (e.g., greater than about 0.8% Fe by mass) or manganese (e.g., greater than about 0.5% Mn by mass). However, such high amounts of iron and/or manganese may reduce the ductility of cast aluminum alloy parts made therefrom, which may prevent such alloys from being used to manufacture certain structural component parts, such as in the automotive industry. For example, when casting aluminum alloy parts, sufficiently high ductility may be necessary to ensure that the cast parts exhibit excellent crushing or crash performance, even when the parts are designed with thin walls for reduced weight.
Recycling of aluminum alloy parts is desirable for energy savings and sustainability. Compositionally closed loop recycling operations, where the composition of the input and output aluminum alloy materials is substantially the same (i.e., the same alloying elements are present in substantially the same amounts in the input and output materials) are specifically desirable because they have the potential to eliminate downcycling (or upcycling) of aluminum alloy scrap materials. In downcycling, mixing of a variety of different aluminum alloy scrap materials may lead to the accumulation of impurities and alloying elements in the recycled aluminum alloy materials, which may limit the downstream use of the recycled materials to lower purity uses. For example, aluminum alloys compositions used in high pressure die casting processes oftentimes contain relatively high amounts of iron and manganese, as compared to aluminum alloy parts cast via relatively low pressure casting processes (e.g., in the manufacture of load-bearing structural component parts), and combining these disparate aluminum alloy compositions during recycling may prevent the resulting recycled aluminum alloy material from being reused to manufacture either of the original aluminum alloy materials. To promote closed loop recycling of aluminum, it would be beneficial to develop an aluminum alloy composition that can be used in multiple types of manufacturing processes to successfully produce aluminum alloy consumer products and/or component parts for a variety of different industries and/or applications.

SUMMARY

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features.
The present disclosure relates to an aluminum alloy for casting shaped aluminum alloy parts. The aluminum alloy comprises, by mass: greater than or equal to about 6.5% to less than or equal to about 8% silicon, greater than or equal to about 0.1% to less than or equal to about 0.4% magnesium, greater than or equal to about 0.2% to less than or equal to about 0.25% iron, greater than or equal to about 0.05% to less than or equal to about 0.15% manganese, and greater than or equal to about 0.10% to less than or equal to about 0.2% chromium. A mass percentage of iron (Fe %), a mass percentage of manganese (Mn %), and a mass percentage of chromium (Cr %) in the aluminum alloy satisfy the following mathematical relationships:

- (i) [Mn %+(a×Cr %)]/Fe %>1, and
- (ii) Fe %+(b×Mn %)+(c×Cr %)>0.6%,
  - where a is greater than or equal to about 1.3 and less than or equal to about 1.7, b is greater than or equal to about 1.2 and less than or equal to about 1.7, and c is greater than or equal to about 2.5 and less than or equal to about 2.9.

In aspects, a may be greater than or equal to about 1.4 and less than or equal to about 1.6, b may be greater than or equal to about 1.4 and less than or equal to about 1.6, and c may be greater than or equal to about 2.6 and less than or equal to about 2.8.
In aspects, a may be about 1.5, b may be about 1.5, and c may be about 2.7.
The aluminum alloy may further comprise, by mass, greater than 0% to less than or equal to 0.2% copper, greater than 0% to less than or equal to 0.2% zinc; and aluminum as balance.
In aspects, the aluminum alloy may comprise, by mass, greater than or equal to about 6.5% to less than or equal to about 7.5% silicon, greater than or equal to about 0.05% to less than or equal to about 0.1% manganese, and greater than or equal to about 0.12% to less than or equal to about 0.18% chromium. In such case, the aluminum alloy may further comprise, by mass, greater than or equal to 0% to less than or equal to 0.1% copper, greater than or equal to 0% to less than or equal to 0.1% zinc and aluminum as balance.
In aspects, the aluminum alloy may comprise, by mass, greater than or equal to about 6.5% to less than or equal to about 7.5% silicon, greater than or equal to about 0.08% to less than or equal to about 0.12% manganese, and greater than or equal to about 0.1% to less than or equal to about 0.15% chromium. In such case, the aluminum alloy may further comprise, by mass, greater than or equal to 0% to less than or equal to 0.1% copper, greater than or equal to 0% to less than or equal to 0.1% zinc, and aluminum as balance.
In aspects, the aluminum alloy may comprise, by mass, greater than or equal to about 6.5% to less than or equal to about 7.5% silicon, greater than or equal to about 0.3% to less than or equal to about 0.4% magnesium, about 0.25% iron, greater than or equal to about 0.08% to less than or equal to about 0.12% manganese, and greater than or equal to about 0.11% to less than or equal to about 0.14% chromium.
After the aluminum alloy is cast into a shaped aluminum alloy part, the shaped aluminum alloy part may exhibit a multiphase microstructure including an aluminum matrix phase and an Fe-containing intermetallic phase distributed throughout the aluminum matrix phase. The Fe-containing intermetallic phase may comprise a plurality of a AlFeSi intermetallic particles and a plurality of Al(M, Fe)Si intermetallic particles, where M is Mn and/or Cr.
In aspects, the Al(M, Fe)Si intermetallic particles may account for, by volume, greater than 50% of the Fe-containing intermetallic phase and the AlFeSi intermetallic particles may account for, by volume, less than 50% of the Fe-containing intermetallic phase.
In aspects, the Al(M, Fe)Si intermetallic particles may account for, by volume, greater than 75% of the Fe-containing intermetallic phase and the AlFeSi intermetallic particles may account for, by volume, less than 25% of the Fe-containing intermetallic phase.
The Al(M, Fe)Si intermetallic particles have a mean aspect ratio of less than 3 when viewed in a two-dimensional cross-section.
The AlFeSi intermetallic particles have a mean aspect ratio of greater than 3 when viewed in a two-dimensional cross-section.
The aluminum alloy may not exhibit die soldering when cast in a steel mold cavity at a temperature of about 705° C.
An aluminum alloy part is disclosed. The aluminum alloy part comprises, by mass: greater than or equal to about 6.5% to less than or equal to about 8% silicon, greater than or equal to about 0.1% to less than or equal to about 0.4% magnesium, greater than or equal to about 0.2% to less than or equal to about 0.25% iron, greater than or equal to about 0.05% to less than or equal to about 0.15% manganese, and greater than or equal to about 0.1% to less than or equal to about 0.2% chromium. A mass percentage of iron (Fe %), a mass percentage of manganese (Mn %), and a mass percentage of chromium (Cr %) in the aluminum alloy satisfy the following mathematical relationships:

- (iii) [Mn %+(a×Cr %)]/Fe %>1, and
- (iv) Fe %+(b×Mn %)+(c×Cr %)>0.6%,
  - where a is greater than or equal to about 1.3 and less than or equal to about 1.7, b is greater than or equal to about 1.2 and less than or equal to about 1.7, and c is greater than or equal to about 2.5 and less than or equal to about 2.9.

In some aspects, the aluminum alloy part may be manufactured via a permanent mold casting process or a sand casting process in which a volume of an aluminum alloy is cast in a mold defining the shape of the aluminum alloy part at a pressure of less than or equal to about 50 psi and then cooled to ambient temperature at an average cooling rate of less than or equal to about 10 degrees Celsius per second. The aluminum alloy part may have a wall thickness of greater than 5 millimeters to less than or equal to about 10 millimeters. In such case, after the aluminum alloy part is solution heat treated and artificially aged, the aluminum alloy part may exhibit a Yield Strength in the range of greater than or equal to about 180 MPa to less than or equal to about 270 MPa, an Ultimate Tensile Strength in the range of greater than or equal to about 260 MPa to less than or equal to about 330 MPa, Fatigue Strength in the range of greater than or equal to about 70 MPa to less than or equal to about 100 MPa, and Elongation at Break in the range of greater than or equal to about 8% to less than or equal to about 13%
In other aspects, the aluminum alloy part may be manufactured by a high-pressure die casting process in which a volume of an aluminum alloy is cast in a mold defining the shape of the aluminum alloy part at a pressure in a range of about 1,500 psi to about 25,400 psi and then cooled to ambient temperature at an average cooling rate in a range of about 100 degrees Celsius per second to about 1,000 degrees Celsius per second. The aluminum alloy part may have a wall thickness of greater than or equal to about 0.5 millimeters to less than about 5 millimeters. In such case, after the aluminum alloy part is cooled to ambient temperature, the aluminum alloy part may exhibit a Yield Strength in the range of greater than or equal to about 100 MPa to less than or equal to about 130 MPa, an Ultimate Tensile Strength in the range of greater than or equal to about 220 MPa to less than or equal to about 280 MPa, and an Elongation at Break in the range of greater than or equal to about 8% to less than or equal to about 17%.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.

FIG. 1 is a scanning electron micrograph image of an Al-7Si-0.25Fe alloy without addition of manganese or chromium.

FIGS. 2A, 2B, and 2C are scanning electron micrograph images of Al-7Si-0.25Fe alloys including, by mass, 0.1%, 0.15%, and 0.2% manganese, respectively.

FIGS. 3A, 3B, and 3C depict scanning electron micrograph images of Al-7Si-0.25Fe alloys including, by mass, 0.1%, 0.15%, and 0.2% chromium, respectively.

FIG. 4 is a scanning electron micrograph image of an Al-7.2Si-0.38Mg-0.11Fe alloy without addition of manganese or chromium.

FIG. 5 is a scanning electron micrograph image of an Al-7.1Si-0.35Mg-0.25Fe-0.14Cr-0.05Mn alloy.

FIG. 6 is a scanning electron micrograph image of an Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy.

FIG. 7 is a Weilbull plot of the probability of stress time percent (in %) vs. stress time percent (STP) for samples of a baseline Al-7.25i-0.38Mg-0.11Fe alloy, where STP is calculated according to the following formula: [(cycle life)/(specified cycle life)]×100%, and where cycle life=the number of cumulative cycles before failure and specified cycle life=the specified cycle count.

FIG. 8 is a Weilbull plot of the probability of STP (in %) vs. STP for samples of an Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy.

FIG. 9 is a plot of engineering stress (MPa) vs. engineering strain (%) for a baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy (shown in dashed lines) and an Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy (shown in solid lines).

FIG. 10 is a plot of plastic work (J/m³) vs. engineering strain (%) for a baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy (shown in dashed lines with square data markers) and an Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy (shown in solid lines with circle-shaped data markers).

FIG. 11 is a plot of weight loss (in grams) vs. dipping duration (in hours) for a baseline Al-7Si-0.8Fe alloy (depicted with square-shaped data markers) and an Al-7Si-0.13Cr-0.1Mn-0.25Fe alloy (depicted with circle-shaped data markers).

FIG. 12 depicts an image of an intact rivet between a sheet of an Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy and a DP590 steel sheet.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.
Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.
When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer, or section discussed below could be termed a second step, element, component, region, layer, or section without departing from the teachings of the example embodiments.
Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s), as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.
Throughout this disclosure, the numerical values represent approximate measures or limits to ranges and encompass minor deviations from the given values and embodiments, having about the value mentioned as well as those having exactly the value mentioned. Other than the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.
In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.
As used herein, the terms “composition” and “material” are used interchangeably to refer broadly to a substance containing at least the preferred chemical constituents, elements, or compounds, but which may also comprise additional elements, compounds, or substances, including trace amounts of impurities, unless otherwise indicated. An “X-based” composition or material broadly refers to compositions or materials in which “X” is the single largest constituent on a weight percentage (%) basis. This may include compositions or materials having, by weight, greater than 50% X, as well as those having, by weight, less than 50% X, so long as X is the single largest constituent of the composition or material based upon its overall weight.
As used herein, the term “aluminum alloy” refers to a material that comprises, by weight, greater than or equal to about 80% or greater than or equal to about 90% aluminum (Al) and one or more other elements (referred to as “alloying” elements) selected to impart certain desirable properties to the material that are not exhibited by pure aluminum.
Aluminum alloy compositions described herein may be represented by a sequence of chemical symbols for the base element (i.e., Al) and its major alloying elements (e.g., Si, Mg, Fe, Mn, and/or Cr), with the alloying elements arranged in order of decreasing mass percent (or alphabetically if percentages are equal). The number preceding the chemical symbol for each alloying element represents the average mass percent of that element in the alloy composition. For example, an aluminum alloy comprising, by mass, 7% silicon (Si), 0.25% iron (Fe), and the balance Al may be represented as Al-7Si-0.25Fe.
Example embodiments will now be described more fully with reference to the accompanying drawings.
The presently disclosed aluminum alloys are formulated to exhibit high soldering resistance during casting without requiring the addition of high amounts of iron or manganese. As such, the presently disclosed aluminum alloys can be used to manufacture cast aluminum alloy parts that exhibit a desirable combination of high ductility and high soldering resistance. In aspects, the presently disclosed aluminum alloys may be referred to as “multipurpose” because such alloys can be used to successfully manufacture both relatively thin-walled parts via high-pressure casting processes, e.g., high pressure die casting processes, and relatively thick-walled parts via relatively low-pressure casting processes. Examples of relatively low-pressure casting processes include permanent mold casting (e.g., low pressure die casting, counter pressure casting, and gravity casting) and sand casting. Aluminum alloy parts cast from the presently disclosed multipurpose aluminum alloy (via either high-pressure casting processes or relatively low-pressure casting processes) exhibit excellent castability and an optimum combination of fatigue strength and fracture toughness, regardless of the type of casting process used to form the aluminum alloy part. In addition, the multipurpose characteristics of the presently disclosed aluminum alloys may allow parts cast from such alloys to be more readily recycled by increasing the number of viable downstream uses for the parts as scrap.
A multipurpose aluminum alloy composition for casting shaped aluminum alloy parts may comprise, in addition to aluminum, alloying elements of silicon (Si), magnesium (Mg), iron (Fe), manganese (Mn), and chromium (Cr), and thus may be referred to herein as an Al—Si—Mg—Fe—Mn—Cr alloy. In aspects, the multipurpose aluminum alloy may comprise, by mass, greater than or equal to about 6.5% or about 7% silicon; less than or equal to about 8% or about 7.5% silicon; or between about 6.5% to about 8% or about 7% to about 7.5% silicon. The multipurpose aluminum alloy may comprise, by mass, greater than or equal to about 0.1% or about 0.15% magnesium; less than or equal to about 0.4% or about 0.35% magnesium; or between about 0.1% to about 0.4% or about 0.15% to about 0.35% magnesium. The multipurpose aluminum alloy may comprise, by mass, greater than or equal to about 0.2% or about 0.22% iron; less than or equal to about 0.25% or about 0.24% iron; or between about 0.2% to about 0.25% or about 0.22% to about 0.24% iron. The multipurpose aluminum alloy may comprise, by mass, greater than or equal to about 0.05% or about 0.08% manganese; less than or equal to about 0.15% or about 0.12% manganese; or between about 0.05% to about 0.15% or about 0.08% to about 0.12% manganese. The multipurpose aluminum alloy may comprise, by mass, greater than or equal to about 0.10% or about 0.12% chromium; less than or equal to about 0.20% or about 0.18% chromium; or between about 0.10% to about 0.20% or about 0.12% to about 0.18% chromium.
The total and respective amounts of Si, Mg, Fe, Mn, and Cr in the multipurpose aluminum alloy are selected to promote aluminum scrap recycling, for example, by allowing aluminum-containing scrap materials to be used as a feedstock material in the production recipe for the alloy and/or by providing the alloy with the ability to be used in the manufacture of a variety of different products, which may allow for the development of closed-loop recycling processes, in which scrap materials are turned into new products without generating waste and without requiring addition of raw materials. In addition, the total and respective amounts of Si, Mg, Fe, Mn, and Cr in the multipurpose aluminum alloy are selected to provide the alloy with certain beneficial properties during casting and to provide aluminum alloy parts made therefrom with certain desirable mechanical and chemical properties, while minimizing the total amount of alloying elements in the alloy. For example, the amount of silicon in the multipurpose aluminum alloy is selected to provide the molten alloy with suitable fluidity for casting, a relatively low melting temperature, excellent dimensional stability, and low thermal expansion. The amount of magnesium in the multipurpose aluminum alloy may be selected to provide the multipurpose aluminum alloy with mechanical strength.
The total and respective amounts of Fe, Mn, and Cr in the multipurpose aluminum alloy are selected to provide the alloy with resistance to soldering during casting and with a desirable combination of high ductility, high strength, fatigue resistance, and fracture toughness, while minimizing the amount of Fe, Mn, and Cr in the multipurpose aluminum alloy. The amount of Fe in the multipurpose aluminum alloy is selected to limit adverse impacts on the microstructure and mechanical properties of aluminum alloy parts made therefrom, while accounting for the presence of Fe as a common impurity in aluminum-containing scrap materials. The amount of Mn in the multipurpose aluminum alloy is selected to compensate for the relatively low amount of Fe in the alloy by providing the alloy with resistance to soldering during casting, to provide aluminum alloy parts made therefrom with a desirable microstructure for improved mechanical properties, and to account for the presence of Mn as an impurity or common addition in certain aluminum-containing scrap materials (e.g., aluminum beverage cans). The amount of Cr in the multipurpose aluminum alloy is selected to compensate for the relatively low amount of Fe in the alloy by providing the alloy with resistance to soldering during casting and to provide aluminum alloy parts made therefrom with a desirable microstructure for improved mechanical properties, while preventing the undesirable formatting of sludge.
Aluminum alloy parts cast from the multipurpose aluminum alloy may exhibit a multiphase microstructure including a face centered cubic (fcc) aluminum matrix phase and one or more Fe-containing intermetallic phases distributed throughout the aluminum matrix phase. The multiphase microstructure of aluminum alloy parts cast from the multipurpose aluminum alloy may include (in addition to the one or more Fe-containing intermetallic phases) one or more silicon-containing eutectic phases distributed throughout the aluminum matrix phase. In the multiphase microstructure of the multipurpose aluminum alloy, the one or more Fe-containing intermetallic phases may be present in regions defined between the aluminum matrix phase and the one or more silicon-containing eutectic phases. The multiphase microstructure of the multipurpose aluminum alloy may be present after the cast part is initially formed and cooled to ambient temperature, or the multiphase microstructure may be developed in the multipurpose aluminum alloy by subjecting the cast part to one or more heat treatment processes (e.g., a solution heat treatment followed by quenching and an artificial aging heat treatment), as discussed further below. The aluminum matrix phase may consist of an aluminum-based material and may not comprise 100% aluminum; instead, the aluminum matrix phase may comprise a solid solution having one or more alloying elements substitutionally and/or interstitially incorporated into an aluminum crystal lattice.
Without intending to be bound by theory, it is believed that the inclusion of Fe in the multipurpose aluminum alloy may result in the formation of an Al-, Fe-, and Si-containing intermetallic phase (referred to herein as an “AlFeSi intermetallic” phase) within the aluminum matrix phase, which may have an adverse effect on the fatigue resistance, fracture toughness, and especially the ductility of aluminum alloy parts made therefrom. Without intending to be bound by theory, it is believed that such adverse effects may be, at least in part, due to the morphology of the micrometer sized AlFeSi intermetallic particles, which may exhibit a monoclinic crystallographic structure. In addition, it is believed that crystal growth of the AlFeSi intermetallic particles during solidification of the melt during casting may primarily occur in two-dimensions, leading to the formation of plate-like structures having high aspect ratios, e.g., aspect ratios greater than 3 when viewed in a two-dimensional cross-section of the aluminum alloy part. Without intending to be bound by theory, it is believed that, when an external force is applied to a cast aluminum alloy part including plate-like AlFeSi intermetallic particles, a fracture can occur in the cast part due to stress concentrations, which may impair the fatigue durability and/or the crash performance of the part. The AlFeSi intermetallic phase is an Al-, Fe-, and Si-based material, meaning that the AlFeSi intermetallic phase primarily comprises the elements Al, Fe, and Si, but also may comprise one or more other elements, e.g., Cr and/or Mn, in relatively small amounts. For example, the combined amounts of Al, Fe, and Si in the AlFeSi intermetallic phase may comprise, by weight, greater than 80%, greater than 90%, or more preferably greater than 95% of the AlFeSi intermetallic phase.
It has been discovered that the formation of an Al-, M-, Fe-, and Si-containing intermetallic phase (referred to herein as an “Al(M, Fe)Si intermetallic” phase), where M is Mn and/or Cr, within the aluminum matrix phase may inhibit the formation of the AlFeSi intermetallic phase. Unlike the AlFeSi intermetallic phase, the Al(M, Fe)Si intermetallic phase may exhibit a cubic crystallographic structure with more uniform surface energy. In addition, growth of Al(M, Fe)Si intermetallic particles within the aluminum matrix phase may generally occur in three-dimensions, which may lead to the formation of intermetallic particles having relatively low aspect ratios, e.g., aspect ratios less than 3 when viewed in a two-dimensional cross-section of the aluminum alloy part. Without intending to be bound by theory, it is believed that formation of the Al(M, Fe)Si intermetallic phase within the aluminum matrix phase may have little to no adverse effect on the fatigue resistance, fracture toughness, or the ductility of the multipurpose aluminum alloy. The Al(M, Fe)Si intermetallic phase is an Al-, Mn-, Cr-. Fe-, and Si-based material, meaning that the Al(M, Fe)Si intermetallic phase primarily comprises the elements Al, Mn, Cr, Fe, and Si. For example, the combined amounts of Al, Mn, Cr, Fe, and Si in the Al(M, Fe)Si intermetallic phase may comprise, by weight, greater than 90% of the Al(M, Fe)Si intermetallic phase.
To ensure aluminum alloy parts cast from the multipurpose aluminum alloy exhibit adequate ductility, fatigue strength, and fracture toughness, the total and respective amounts of Fe, Mn, and Cr in the multipurpose aluminum alloy are selected to promote the formation of an Al(M, Fe)Si intermetallic phase within the aluminum matrix phase and, in effect, to inhibit the formation of the AlFeSi intermetallic phase, while minimizing the overall amount of Fe-containing intermetallic phases within the aluminum matrix phase. At the same time, the amounts of Fe, Mn, and Cr in the multipurpose aluminum alloy are selected to allow for the use of scrap aluminum-containing materials in formulation of the multipurpose aluminum alloy composition, while also limiting the amounts of Fe, Mn, and Cr in the multipurpose aluminum alloy to increase the number of downstream options for recycling aluminum alloy parts cast from the multipurpose aluminum alloy,
Prior to development of the presently disclosed multipurpose aluminum alloy, it was believed that aluminum alloy compositions could be formulated either (i) to exhibit good soldering resistance, particularly in high pressure die casting processes, by addition of relatively large amounts of Fe and/or Mn, or (ii) to provide aluminum alloy parts made therefrom with high ductility and high fatigue strength, particularly in relatively low pressure casting processes, by limiting the amount of transition metal elements (e.g., Fe, Mn, and Cr) in the alloy compositions to less than 0.15% by mass. The presently disclosed multipurpose aluminum alloy can be used to form cast aluminum alloy parts with high ductility while also allowing for the inclusion of up to, by mass, 0.6% Fe, Mn, and Cr in total in the multipurpose aluminum alloy composition. To accomplish this, it has been found that the combined amounts, by mass, of Mn and Cr in the multipurpose aluminum alloy should be selected or controlled to compensate for the relatively high mass fraction of Fe in the multipurpose aluminum alloy, without adding an excess amount of Mn and/or Cr thereto. When Mn is added to a Si- and Fe-containing aluminum alloy, it has been found that a mass ratio of Mn to Fe of greater than or equal to about 1 to 1.5 is sufficient to inhibit the formation of AlFeSi intermetallic particles in cast parts made from the Si- and Fe-containing aluminum alloy. In addition, it has been found that when equivalent amounts of Cr and Mn are added to Si- and Fe-containing aluminum alloys, Cr is more effective than Mn in suppressing the formation of an AlFeSi intermetallic phase. Therefore, when Cr is added to a Si- and Fe-containing aluminum alloy, it has been found that a mass ratio of Cr to Fe of greater than or equal to about 0.5 to 0.8 is sufficient to inhibit the formation of AlFeSi intermetallic particles in cast parts made from the Si- and Fe-containing aluminum alloy.
To ensure that the multipurpose aluminum alloy can be used to form cast aluminum alloy parts with adequate ductility, it has been found that the mass percentage of iron (Fe %), the mass percentage of manganese (Mn %), and the mass percentage of chromium (Cr %) in the multipurpose aluminum alloy should be selected or controlled to satisfy the following mathematical relationship:
$\begin{matrix} \frac{Mn % + (a \times Cr %)}{Fe %} > 1 & (1) \end{matrix}$
where a is greater than or equal to about 1.3 or about 1.4; less than or equal to about 1.7 or about 1.6; or between about 1.3 to about 1.7 or about 1.4 to about 1.6. In aspects, a is about 1.5.
To avoid the formation of undesirable coarse sludge and to minimize the total volume fraction of Fe-containing intermetallic phases in the multipurpose aluminum alloy, the mass percentage of manganese should be greater than or equal to about 0.05% or greater than or equal to about 0.08%, and the mass percentage of chromium should be less than or equal to about 0.20% or less than or equal to about 0.18% chromium, based upon the overall mass of the multipurpose aluminum alloy.
When the mass percentages of Fe, Mn, and Cr in the multipurpose aluminum alloy are selected or controlled to satisfy the mathematical relationship set forth in formula (1), aluminum alloy parts cast from the multipurpose aluminum alloy may include an Fe-containing intermetallic phase distributed throughout an aluminum matrix phase, and the Fe-containing intermetallic phase may comprise a plurality of AlFeSi intermetallic particles and a plurality of Al(M, Fe)Si intermetallic particles. In addition, the Al(M, Fe)Si intermetallic phase may comprise the dominant Fe-containing intermetallic phase within the aluminum matrix phase. In other words, the Al(M, Fe)Si intermetallic particles may account for, by volume, greater than 50% of the Fe-containing intermetallic phase and the AlFeSi intermetallic particles may account for, by volume, less than 50% of the Fe-containing intermetallic phase. In aspects, the Al(M, Fe)Si intermetallic particles may account for, by volume, greater than 75% of the Fe-containing intermetallic phase and the AlFeSi intermetallic particles may account for, by volume, less than 25% of the Fe-containing intermetallic phase.
In some aluminum alloys, Fe, Mn, and/or Cr have been included in the alloy compositions in relatively large amounts to ensure the alloys exhibit adequate resistance to soldering during casting. For example, Fe has been added to Si-containing aluminum alloy compositions in an amount, by mass, greater than or equal to about 0.8% of the overall alloy to ensure adequate soldering resistance. As another example, Mn has been added to Si-containing aluminum alloy compositions in an amount, by mass, greater than or equal to about 0.5% of the overall alloy to ensure adequate soldering resistance. Alternatively, a combination of, by mass, about 0.13% Fe and about 0.45% Mn may be added to Si-containing aluminum alloy compositions to ensure adequate soldering resistance. As another alternative, a combination of, by mass, about 0.13% Fe and about 0.25% Cr may be added to Si-containing aluminum alloy compositions to ensure adequate soldering resistance. Because a combination of, by mass, about 0.13% Fe and about 0.45% Mn may be added to Si-containing aluminum alloy composition (instead of, by mass, 0.8% Fe) to ensure adequate soldering resistance, it has been determined that, by mass, Mn is about 1.49 times as effective in preventing die sticking as Fe is in preventing die sticking. In addition, because a combination of, by mass, about 0.13% Fe and about 0.25% Cr may be added to Si-containing aluminum alloy composition (instead of, by mass, 0.8% Fe) to ensure adequate soldering resistance, it has been determined that, by mass, Cr is about 2.68 times as effective in preventing die sticking as Fe is in preventing die sticking. Assuming that if an Si-containing aluminum alloy composition that is substantially free of Mn and Cr must contain, by mass, at least 0.8% Fe to ensure adequate soldering resistance, then, based upon the above relationships, a mathematical relationship between the respective and overall amounts of Fe, Mn, and Cr in an Si-, Fe-, Mn-, and Cr-containing aluminum alloy composition can be determined.
To ensure that the multipurpose aluminum alloy exhibits adequate resistance to soldering, it has been found that the mass percentage of iron (Fe %), the mass percentage of manganese (Mn %), and the mass percentage of chromium (Cr %) in the multipurpose aluminum alloy should be selected or controlled to satisfy the following mathematical relationship:
Fe %+(b×Mn %)+(c×Cr %)>0.60% (2)
where b is greater than or equal to about 1.2 or about 1.4, less than or equal to about 1.7 or about 1.6, or between about 1.2 to about 1.7 or about 1.4 to about 1.6; and where c is greater than or equal to about 2.5 or about 2.6, less than or equal to about 2.9 or about 2.8, or between about 2.8 to about 2.9 or about 2.6 to about 2.8. In aspects, b is about 1.5 and c is about 2.7.
In aspects, the multipurpose aluminum alloy may comprise, by mass, greater than or equal to about 0% or about 0.05% copper (Cu); less than or equal to about 0.2% or about 0.1% copper; or between about 0% to about 0.2% or about 0.05% to about 0.1% copper. The amount of copper in the multipurpose aluminum alloy may depend upon the amount of copper in the raw or scrap materials used to prepare the multipurpose aluminum alloy composition and/or on the intended use of the multipurpose aluminum alloy.
In aspects, the multipurpose aluminum alloy may comprise, by mass, greater than or equal to about 0% or about 0.05% zinc (Zn); less than or equal to about 0.2% or about 0.1% zinc; or between about 0% to about 0.2% or about 0.05% to about 0.1% zinc. The amount of zinc in the multipurpose aluminum alloy may depend upon the amount of zinc in the raw or scrap materials used to prepare the multipurpose aluminum alloy composition and/or on the intended use of the multipurpose aluminum alloy.
Additional elements not intentionally introduced into the composition of the multipurpose aluminum alloy nonetheless may be inherently present in the alloy in relatively small amounts, for example, less than 0.2%, preferably less than 0.05%, and more preferably less than 0.01% by weight of the multipurpose aluminum alloy. Such elements may be present, for example, as impurities in the raw or scrap materials used to prepare the multipurpose aluminum alloy composition. In embodiments where the multipurpose aluminum alloy is referred to as comprising one or more alloying elements (e.g., one or more of Si, Mg, Fe, Mn, Cr, Cu, and Zn) and aluminum as balance, the term “as balance” does not exclude the presence of additional elements not intentionally introduced into the composition of the multipurpose aluminum alloy but nonetheless inherently present in the alloy in relatively small amounts, e.g., as impurities.
The multipurpose aluminum alloy may be used in a variety of casting processes to manufacture shaped parts for a variety of industries, including the automotive industry. For example, the presently disclosed aluminum alloys may be used to manufacture shaped parts via high-pressure casting processes (e.g., high pressure die casting processes) and via relatively low-pressure casting processes (e.g., permanent mold casting, including low pressure die casting, counter pressure casting, and gravity casting, and sand casting). Examples of automotive parts that may be cast from the presently disclosed aluminum alloys include vehicle body components, engine blocks, cylinder heads, pistons, connecting rods, transmission housings, wheel hubs, pump housings, carburetor housings, valve covers, steering gear housings, clutch housings, air intake and exhaust gas manifolds, and oil pans, to name a few. Cast parts having a wall thickness of less than 5 millimeters (e.g., greater than or equal to about 0.5 millimeters and less than or equal to about 4 millimeters) may be referred to as “thin-walled,” and cast parts having a wall thickness of greater than 5 millimeters may be referred to as “thick-walled.”
The multipurpose aluminum alloy may be heated at a temperature in a range of about 650° C. to about 730° C. (e.g., about 705° C.) to form a melt of molten aluminum alloy. The temperature at which the multipurpose aluminum alloy is cast may depend upon the specific composition of the alloy and/or on the wall thickness of the part being cast. A volume of the molten aluminum alloy may be poured into a mold cavity and allowed to cool and solidify in the mold cavity. After solidification, the cast part may be removed from the mold cavity and allowed to cool to ambient temperature. In aspects, thin-walled aluminum alloy parts may be manufactured via high-pressure die casting processes and may experience an average cooling rate in a range of about 100 degrees Celsius per second to about 1,000 degrees Celsius per second. In other aspects, relatively thick-walled aluminum alloy parts may be manufactured via casting processes that do not require application of a high gauge pressure to melt in the mold cavity, (e.g., permanent mold casting processes, including low pressure die casting, counter pressure casting, and gravity casting, and sand casting processes). Relatively thick-walled aluminum alloy parts cast via such relatively low-pressure, or no pressure casting processes may experience an average cooling rate of less than or equal to about 10 degrees Celsius per second during the casting process. In aspects, relatively thick-walled aluminum alloy parts cast via such relatively low-pressure, or no pressure casting processes may experience a cooling rate in a range of about 1 degree Celsius per second to about 10 degrees Celsius per second during the casting process. Both thin-walled aluminum alloy parts and relatively thick-walled aluminum alloy parts may be manufactured from the presently disclosed multipurpose aluminum alloy, respectively, via high-pressure die casting processes and via relatively low-pressure or no pressure casting processes.
In aspects, after the cast part has been cooled to ambient temperature, the cast part may be subjected to one or more heat treatment processes, for example, to increase the Vickers hardness thereof. Example heat treatment processes may include a solution heat treatment, an artificial aging heat treatment, or a combination thereof. The solution heat treatment may be performed by heating the cast aluminum alloy part at a temperature in a range of about 440° C. to about 550° C. for a duration in a range of about 1 hours to 12 hours to bring the alloying elements (e.g., Si, Mg, Fe, Mn, Cr, Cu, and/or Zn) into solid solution with the aluminum matrix phase. After the solution heat treatment, the cast part may be quenched to a temperature in a range of about 50° C. to about 100° C. The artificial aging heat treatment may be performed by heating the cast aluminum alloy part at a temperature in a range of about 160° C. to about 240° C. for a duration in a range of about 3 hours to 12 hours to form one or more precipitate phases within the aluminum matrix phase. The specific heat treatment temperatures and durations may depend upon the wall thickness of the cast part and the intended application of the cast part.
Aluminum alloy parts cast from the multipurpose aluminum alloy may exhibit different mechanical properties depending on the casting method used to form the aluminum alloy part and/or whether the aluminum alloy part was subjected to any heat treatment processes after casting. For example, after a thick-walled aluminum alloy part is cast from the multipurpose aluminum alloy using a relatively low pressure casting process followed by a solution heat treatment and an artificially aging heat treatment, the thick-walled aluminum alloy part may exhibit a Yield Strength in the range of greater than or equal to about 180 MPa to less than or equal to about 270 MPa, an Ultimate Tensile Strength in the range of greater than or equal to about 260 MPa to less than or equal to about 330 MPa, Fatigue Strength in the range of greater than or equal to about 70 MPa to less than or equal to about 100 MPa, and Elongation at Break in the range of greater than or equal to about 8% to less than or equal to about 13%. On the other hand, a thin-walled aluminum alloy part cast from the multipurpose aluminum alloy using a high pressure die casting process without any subsequent heat treatments (i.e., without being subjected to a solution heat treatment or an artificially aging heat treatment) may exhibit a Yield Strength in the range of greater than or equal to about 100 MPa to less than or equal to about 130 MPa, an Ultimate Tensile Strength in the range of greater than or equal to about 220 MPa to less than or equal to about 280 MPa, and an Elongation at Break in the range of greater than or equal to about 8% to less than or equal to about 17%.

EXAMPLES

Example 1: Effect of Cr and Mn on Morphology of Fe-containing Intermetallic Particles

Al-7Si-0.25Fe alloys including different amounts of manganese and chromium were prepared in a laboratory environment, formed into samples via gravity casting and the microstructure of the cast samples was observed using scanning electron micrography at 200X magnification. For each scanning electrograph image, the aspect ratio of more than 600 Fe-containing intermetallic particles was measured and the percentage of Fe-containing intermetallic particles having an aspect ratio of greater than 3 was determined.
FIG. 1 depicts a scanning electron micrograph (SEM) image of an Al-7Si-0.25Fe alloy without addition of manganese or chromium. The average aspect ratio of the Fe-containing intermetallic particles in the Al-7Si-0.25Fe alloy was 3.0±0.3. In the SEM image, the Fe-containing intermetallic particles appear light in color or white, in contrast to the generally black aluminum matrix phase.
FIGS. 2A, 2B, and 2C depict scanning electron micrograph images of Al-7Si-0.25Fe alloys including, by mass, 0.10%, 0.15%, and 0.20% manganese, respectively. The average aspect ratio of the Fe-containing intermetallic particles in the Al-7Si-0.25Fe-0.10Mn alloy (FIG. 2A) was 3.0±0.2 with 44% of the Fe-containing intermetallic particles having an aspect ratio of greater than 3. The average aspect ratio of the Fe-containing intermetallic particles in the Al-7Si-0.25Fe-0.15Mn alloy (FIG. 2B) was 2.7±0.2 with 38% of the Fe-containing intermetallic particles having an aspect ratio of greater than 3. The average aspect ratio of the Fe-containing intermetallic particles in the Al-7Si-0.25Fe-0.20Mn alloy (FIG. 2C) was 2.7±0.2 with 39% of the Fe-containing intermetallic particles having an aspect ratio of greater than 3.
FIGS. 3A, 3B, and 3C depict scanning electron micrograph images of Al-7Si-0.25Fe alloys including, by mass, 0.10%, 0.15%, and 0.20% chromium, respectively. The average aspect ratio of the Fe-containing intermetallic particles in the Al-7Si-0.25Fe-0.10Cr alloy (FIG. 3A) was 2.3±0.2 with 26% of the Fe-containing intermetallic particles having an aspect ratio of greater than 3. The average aspect ratio of the Fe-containing intermetallic particles in the Al-7Si-0.25Fe-0.15Cr alloy (FIG. 3B) was 2.2±0.1 with 22% of the Fe-containing intermetallic particles having an aspect ratio of greater than 3. The average aspect ratio of the Fe-containing intermetallic particles in the Al-7Si-0.25Fe-0.20Cr alloy (FIG. 3C) was unable to be determined due to the formation of sludge. These results indicate that Cr is much more effective than Mn in modifying the morphology of the Fe-containing intermetallic phases in aluminum alloy compositions, in particular, by suppressing the formation of AlFeSi intermetallic phases.

Example 2: Optimizing Mn content for Al-7Si-0.25Fe-0.14Cr alloy

Aluminum alloy samples including different amounts of Fe, Cr, and Mn were prepared in a production environment, formed into samples via counter-pressure casting, the Yield Strength and Elongation-to-Fracture were measured via uniaxial tensile tests, and the microstructure of the cast samples was observed using scanning electron micrography at 200X magnification. Prior to evaluation and testing, the samples were subjected to a T6 heat treatment including a solution heat treatment at 540° C. for 5 hours followed by water quench at 65° C. and then ageing heat treatment at 166° C. for 4 hours.
FIG. 4 depicts a scanning electron micrograph image of an Al-7.2Si-0.38Mg-0.11Fe alloy without addition of manganese or chromium. The Al-7.2Si-0.38Mg-0.11Fe alloy exhibited a Yield Strength of 248 MPa and an Elongation-to-Fracture of 8.6%.
FIG. 5 depicts a scanning electron micrograph image of an Al-7.1Si-0.35Mg-0.25Fe-0.14Cr-0.05Mn alloy. The Al-7.1Si-0.35Mg-0.25Fe-0.14Cr-0.05Mn alloy exhibited a Yield Strength of 248 MPa and an Elongation-to-Fracture of 6.5%.
FIG. 6 depicts a scanning electron micrograph image of an Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy. The Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy exhibited a Yield Strength of 247 MPa and an Elongation-to-Fracture of 8.0%.

Example 3: Fatigue Resistance

A baseline an Al-7.25i-0.38Mg-0.11Fe alloy and an Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy were prepared in a production environment, formed into samples via counter-pressure casting, and evaluated for fatigue resistance. Prior to evaluation and testing, the samples were subjected to a T6 heat treatment including a solution heat treatment at 540° C. for 5 hours followed by water quench at 65° C. and then ageing heat treatment at 166° C. for 4 hours.
Samples were tested for fatigue resistance, with each sample starting at a stress amplitude equal to a specified fatigue strength (100 MPa) and loaded for a specified number of cycles (1 million cycles), then retested at successively higher stress amplitudes increasing in equal 10% increments for cycle counts equaling 10% of the number originally specified. The test for each sample ends when it fractures. The tests were performed fully-reversed (R=−1); sinusoidal waveform in load control; and in laboratory air. Stress time percent statistic (STP) was calculated for each sample according to the following equation: STP=[(cycle life)/(specified cycle life)]×100%, where the cycle life=the number of cumulative cycles before failure and the specified cycle life=the specified cycle count (i.e., 1 million cycles).
FIG. 7 depicts a Weilbull plot of the probability of STP (in %) vs. STP for samples of the baseline Al-7.2Si-0.38Mg-0.11Fe alloy. The samples of the baseline Al-7.2Si-0.38Mg-0.11Fe alloy had an average STP of 1.21±0.28 and a median STP of 1.22.
FIG. 8 depicts a Weilbull plot of the probability of STP (in %) vs. STP for samples of the Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy. The samples of the Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy had an average STP of 1.41±0.40 and a median STP of 1.41.
The Al-6.6Si-0.34Mg-0.25Fe-0.14Cr-0.12Mn alloy exhibited better fatigue performance than the baseline Al-7.2Si-0.38Mg-0.11Fe alloy.

Example 4: Uniaxial Tensile Testing

A baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy and an Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy were prepared in a laboratory environment, formed into samples via high-pressure die casting, and evaluated via uniaxial tensile testing. Prior to evaluation and testing, the baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy was T7 heat treated including a solution heat treatment at 460° C. for 60 minutes followed by a fan quench and then an artificial ageing heat treatment at 215° C. for 120 minutes. In practice, T7 heat treatments are generally considered to be costly and are thus oftentimes avoided if doing so will not sacrifice ductility. The Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy was tested in the as-cast condition after being cooled to ambient temperature without being subjected to any further heat treatments.
FIG. 9 depicts a plot of engineering stress (MPa) vs. engineering strain (%) for the baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy (shown in dashed lines) and the Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy (shown in solid lines). The baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy exhibited a Yield Strength of 126 MPa, an Ultimate Tensile Strength of 203 MPa, and an Elongation at Fraction of 15.0%. The Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy exhibited a Yield Strength of 107 MPa, an Ultimate Tensile Strength of 254 MPa, and an Elongation at Fraction of 13.3%.
FIG. 10 depicts a plot of plastic work (J/m³) vs. engineering strain (%) for the baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy (shown in dashed lines with square data markers) and the Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy (shown in solid lines with circle-shaped data markers). The results indicate that the presently disclosed Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy, even in the as-cast condition without further heat treatment) exhibits better energy absorption capabilities than the T7 heat-treated baseline Al-10.5Si-0.28Mg-0.12Fe-0.49Mn alloy.

Example 5: Die Sticking Resistance Evaluation

A baseline Al-7Si-0.8Fe alloy melt and an Al-7Si-0.13Cr-0.1Mn-0.25Fe alloy melt were prepared in a laboratory environment and subjected to a dipping test performed at 705° C. to determine their respective reactivities with die steel. Pins made of die steel were weighted before and after being dipped into the as-prepared melts for designated periods of time. The difference between the weight of the pins before and after being dipped (the weight loss of the pins) is due to the occurrence of a chemical reaction between the pins and aluminum alloy melts. Four pins were applied for calculating average data for each alloy melt. FIG. 11 depicts a plot of weight loss (in grams) vs. dipping duration (in hours); the results of the baseline Al-7Si-0.8Fe alloy are depicted as squares and the results of the Al-7Si-0.13Cr-0.1Mn-0.25Fe alloy are depicted as circles.
The multipurpose aluminum alloy may exhibit high soldering resistance at relatively low iron contents (e.g., ≤about 0.25 mass % iron). For example, the soldering resistance of the multipurpose aluminum alloy may be similar to an aluminum alloy that comprises, by mass, about 7% silicon, about 0.8% iron, and aluminum as balance. In aspects, the multipurpose aluminum alloy may not exhibit die soldering (sticking) when cast in a steel mold cavity at a temperature of about 705° C.

Example 6: Riveting to Steel

FIG. 12 depicts an image of a successful rivet between a sheet of an Al-7.3Si-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy having a thickness of about 3 millimeters and a DP590 steel sheet having a thickness of about 0.7 millimeters. The Al-7.35i-0.15Mg-0.25Fe-0.11Cr-0.08Mn alloy sheet was rivetted to the DP590 steel sheet in the as-cast condition after being cooled to ambient temperature without being subjected to any further heat treatments No cracks were formed in either of the sheets during the riveting process, indicating that the presently disclosed multipurpose aluminum alloy may be successfully joined to a steel sheet by riveting.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

1. An aluminum alloy for casting shaped aluminum alloy parts, the aluminum alloy comprising, by mass:

greater than or equal to about 6.5% to less than or equal to about 8% silicon;

greater than or equal to about 0.1% to less than or equal to about 0.4% magnesium;

greater than or equal to about 0.2% to less than or equal to about 0.25% iron;

greater than or equal to about 0.05% to less than or equal to about 0.15% manganese; and

greater than or equal to about 0.1% to less than or equal to about 0.2% chromium, wherein a mass percentage of iron (Fe %), a mass percentage of manganese (Mn %), and a mass percentage of chromium (Cr %) in the aluminum alloy satisfy the following mathematical relationships:

(i) [Mn %+(a×Cr %)]/Fe %>1, and

(ii) Fe %+(b×Mn %)+(c×Cr %)>0.6%,

where a is greater than or equal to about 1.3 and less than or equal to about 1.7, b is greater than or equal to about 1.2 and less than or equal to about 1.7, and c is greater than or equal to about 2.5 and less than or equal to about 2.9.

2. The aluminum alloy of claim 1, wherein a is greater than or equal to about 1.4 and less than or equal to about 1.6, b is greater than or equal to about 1.4 and less than or equal to about 1.6, and c is greater than or equal to about 2.6 and less than or equal to about 2.8.

3. The aluminum alloy of claim 1, wherein a is about 1.5, b is about 1.5, and c is about 2.7.

4. The aluminum alloy of claim 1, wherein the aluminum alloy further comprises, by mass:

greater than 0% to less than or equal to 0.2% copper;

greater than 0% to less than or equal to 0.2% zinc; and

aluminum as balance.

5. The aluminum alloy of claim 1, wherein the aluminum alloy comprises, by mass:

greater than or equal to about 6.5% to less than or equal to about 7.5% silicon;

greater than or equal to about 0.05% to less than or equal to about 0.1% manganese;

greater than or equal to about 0.12% to less than or equal to about 0.18% chromium;

greater than or equal to 0% to less than or equal to 0.1% copper;

greater than or equal to 0% to less than or equal to 0.1% zinc; and

aluminum as balance.

6. The aluminum alloy of claim 1, wherein the aluminum alloy comprises, by mass:

greater than or equal to about 0.08% to less than or equal to about 0.12% manganese;

greater than or equal to about 0.10% to less than or equal to about 0.15% chromium;

greater than or equal to 0% to less than or equal to 0.1% copper;

greater than or equal to 0% to less than or equal to 0.1% zinc; and

aluminum as balance.

7. The aluminum alloy of claim 1, wherein the aluminum alloy comprises, by mass:

greater than or equal to about 0.3% to less than or equal to about 0.4% magnesium;

about 0.25% iron;

greater than or equal to about 0.08% to less than or equal to about 0.12% manganese; and

greater than or equal to about 0.11% to less than or equal to about 0.14% chromium.

8. The aluminum alloy of claim 1, wherein, after the aluminum alloy is cast into a shaped aluminum alloy part, the aluminum alloy exhibits a multiphase microstructure including an aluminum matrix phase and an Fe-containing intermetallic phase distributed throughout the aluminum matrix phase, and wherein the Fe-containing intermetallic phase comprises a plurality of a AlFeSi intermetallic particles and a plurality of Al(M, Fe)Si intermetallic particles, where M is Mn and/or Cr.

9. The aluminum alloy of claim 8, wherein the Al(M, Fe)Si intermetallic particles account for, by volume, greater than 50% of the Fe-containing intermetallic phase and the AlFeSi intermetallic particles account for, by volume, less than 50% of the Fe-containing intermetallic phase.

10. The aluminum alloy of claim 9, wherein the Al(M, Fe)Si intermetallic particles account for, by volume, greater than 75% of the Fe-containing intermetallic phase and the AlFeSi intermetallic particles account for, by volume, less than 25% of the Fe-containing intermetallic phase.

11. The aluminum alloy of claim 9, wherein the Al(M, Fe)Si intermetallic particles have a mean aspect ratio of less than 3 when viewed in a two-dimensional cross-section.

12. The aluminum alloy of claim 9, wherein the AlFeSi intermetallic particles have a mean aspect ratio of greater than 3 when viewed in a two-dimensional cross-section.

13. The aluminum alloy of claim 1, wherein the aluminum alloy does not exhibit die soldering when cast in a steel mold cavity at a temperature of about 705° C.

14. An aluminum alloy part comprising, by mass:

greater than or equal to about 6.5% to less than or equal to about 8% silicon;

greater than or equal to about 0.2% to less than or equal to about 0.25% iron;

greater than or equal to about 0.1% to less than or equal to about 0.2% chromium, wherein a mass percentage of iron (Fe %), a mass percentage of manganese (Mn %), and a mass percentage of chromium (Cr %) in(Cr %)in the aluminum alloy satisfy the following mathematical relationships:

(i) [Mn %+(a×Cr %)]/Fe %>1, and

(ii) Fe %+(b×Mn %)+(c×Cr %)>0.6%,

15. The aluminum alloy part of claim 14, wherein the aluminum alloy part is manufactured via a permanent mold casting process or a sand casting process in which a volume of an aluminum alloy is cast in a mold defining the shape of the aluminum alloy part at a pressure of less than or equal to about 50 psi and then cooled to ambient temperature at an average cooling rate of less than or equal to about 10 degrees Celsius per second.

16. The aluminum alloy part of claim 15, wherein the aluminum alloy part has a wall thickness of greater than 5 millimeters to less than or equal to about 10 millimeters.

17. The aluminum alloy part of claim 16, wherein, after the aluminum alloy part is solution heat treated and artificially aged, the aluminum alloy part exhibits a Yield Strength in the range of greater than or equal to about 180 MPa to less than or equal to about 270 MPa, an Ultimate Tensile Strength in the range of greater than or equal to about 260 MPa to less than or equal to about 330 MPa, Fatigue Strength in the range of greater than or equal to about 70 MPa to less than or equal to about 100 MPa, and Elongation at Break in the range of greater than or equal to about 8% to less than or equal to about 13%.

18. The aluminum alloy part of claim 14, wherein the aluminum alloy part is manufactured via a high-pressure casting process in which a volume an aluminum alloy is cast in a mold defining the shape of the aluminum alloy part at a pressure in a range of about 1,500 psi to about 25,400 psi and then cooled to ambient temperature at an average cooling rate in a range of about 100 degrees Celsius per second to about 1,000 degrees Celsius per second.

19. The aluminum alloy part of claim 18, wherein the aluminum alloy part has a wall thickness of greater than or equal to about 0.5 millimeters to less than about 5 millimeters.

20. The aluminum alloy part of claim 19, wherein, after the aluminum alloy part is cooled to ambient temperature, the aluminum alloy part exhibits a Yield Strength in the range of greater than or equal to about 100 MPa to less than or equal to about 130 MPa, an Ultimate Tensile Strength in the range of greater than or equal to about 220 MPa to less than or equal to about 280 MPa, and an Elongation at Break in the range of greater than or equal to about 8% to less than or equal to about 17%.