Aluminum alloy suitable for high-pressure casting

Abstract

Aluminum alloy suitable for high-pressure casting and capable of hardening at elevated temperatures, the alloy containing: at least 84 percent by weight of aluminium (Al); 9.5 to 13 percent by weight silicon (Si); 0.2 to 0.6 percent by weight of magnesium (Mg); and also 0.1 to 2 percent by weight of iron (Fe); Contains 0.1 to 2 percent by weight of manganese (Mn); where the weight percent ratio Mn:Fe is 0.5 to 3 and the total amount of Mn + Fe is 0.5 to 2.0 weight percent; and the alloy is essentially free of copper (Cu), with the copper content being < 0.01 percent by weight; and The alloy exhibits a eutectic phase in the range of 15-16 volume percent and hardening occurs in a temperature range of 500 °C to 650 °C.

Description

AREA OF INVENTION

[0001] The invention relates generally to a copper-free aluminium alloy suitable for high-pressure die casting (HPDC) and to the castings made therefrom, which can harden at elevated temperatures with reduced porosity, thereby possessing superior mechanical properties for applications, particularly in the automotive industry. BACKGROUND OF THE INVENTION

[0002] HPDC is a cost-effective and widely used process for the industrial production of metal components requiring precise dimensions, tight tolerances, and a smooth surface finish. Manufacturers in the automotive industry are increasingly required to produce near-net-shape aluminum components with a combination of high tensile strength and ductility, and HPDC provides the most economical production method for large-scale production of small to medium-sized components.

[0003] Aluminum alloy castings constitute the majority of HPDC castings and are found, for example, in a wide range of automotive parts. To avoid discontinuities in the casting, the molten alloy is injected into the mold cavity quickly enough to fill the entire cavity before any part of it begins to solidify. This injection is therefore carried out under high pressure, and the molten metal is subjected to swirling currents as it is forced into the mold and subsequently solidifies rapidly. Because the air displaced by the molten alloy has little time to escape, some of it becomes trapped, resulting in porosity. Castings also contain pores resulting from gas vapor decomposition products of the organic mold wall lubricants, and further porosity can result from shrinkage during solidification.

[0004] A major disadvantage of the porosity resulting from the HPDC process is that aluminum alloy castings made from aluminum, which normally exhibits the ability to age, cannot be artificially hardened; that is, they cannot be treated at the high temperatures characteristic of artificial aging conditions. The internal pores, which contain gases or gas-forming components within the high-pressure castings, expand during conventional solution treatment at elevated temperatures, leading to the formation of surface blisters on the castings. The presence of these blisters not only affects the appearance of the castings but also their dimensional stability and, in some cases, can adversely affect the specific mechanical properties of HPDC components.Specifically, aluminum alloy HPDC castings are not amenable to high-temperature solution treatment (T4), for example, 500 °C, which significantly reduces the potential for precipitation hardening through a full T6 and / or T7 temper treatment (also referred to as a combination of T4 and T5 temper treatments). It is virtually impossible to find a conventionally processed HPDC component without large gas bubbles.

[0005] In Al-Si casting alloys (for example, alloys 319, 356, 390, 360, 380), an increase in strength is achieved through post-cast heat treatment with the addition of various dissolved alloy-hardening substances, including, but not limited to, Cu and Mg. The heat treatment of cast aluminum involves a mechanism described as hardening or precipitation strength enhancement.Heat treatment (conventional T6 and / or T7 heat treatment) generally comprises at least one step or a combination of three steps: (1) solution treatment (also defined as T4) at a relatively high temperature below the melting point of the alloy, often for times exceeding 8 hours or more, to dissolve its alloying (solute) elements and homogenize or modify the microstructure; (2) rapid cooling or quenching in a cold or warm liquid medium, for example water, after solution treatment to retain the dissolved elements in a supersaturated solid solution; and (3) artificial hardening (T5) by holding the alloy for a period of time at an intermediate temperature suitable for achieving hardening or strength enhancement by precipitation or deposition.A solution treatment (T4) serves three main purposes: (1) dissolving elements that will later cause hardening, (2) spheroidizing undissolved constituents, and (3) homogenizing the concentrations of dissolved substances in the material. Quenching after T4 solution treatment retains the dissolved substance elements in a supersaturated solid solution (SSS) and also creates a supersaturation of defects, which enhances diffusion and dispersion of precipitation. To maximize the strength of the alloy, the precipitation of all strength-enhancing phases during quenching should be prevented. Hardening (T5, either natural or artificial) produces a controlled dispersion of strength-enhancing precipitates.

[0006] With T5 curing, there are generally three types of curing conditions (see Fig. 1) These are commonly referred to as underaging, peak aging, and overaging. During pre-hardening or an initial stage of hardening, Guinier-Preston (GP) zones and fine shearable precipitates form, and the casting is considered under-hardened. In this state, the mechanical properties of the casting, such as material hardness and yield strength, are typically inferior. Extended time at a given temperature or hardening at a higher temperature further develops the precipitate structure, improving the mechanical properties, such as hardness and yield strength, to maximum levels to achieve the peak aging / hardness state. Further aging reduces the hardness / yield strength, and the casting becomes over-hardened through precipitate coarsening and crystallographic incoherence transformation. Fig. Figure 2 shows an example of the hardening responses of cast aluminum alloys A356 / 357, which were hardened at a temperature of 170 °C. During the investigated hardening period at a given hardening temperature, the castings go through underhardened, peak-hardened, and overhardened states.

[0007] Given that conventional HPDC aluminum components inevitably exhibit internal porosity, artificial hardening (T5) can be a crucial step in achieving the desired mechanical properties without blistering. The strength increase resulting from hardening occurs because the retained hardening solutes present in the supersaturated solid solution form precipitates that are finely dispersed within the grains, enhancing the casting's resistance to deformation by slip and creep. Maximum hardening, or strength increase, can be achieved if the hardening treatment results in the formation of a critical dispersion of at least one type of these fine precipitates.

[0008] Furthermore, in conventional HPDC processes, castings are often slowly cooled to a low temperature, for example, below 200 °C, before ejection from the mold and quenching. This significantly reduces the subsequent hardening potential, as the solubility of hardening solvents decreases considerably with decreasing quenching temperature. As a result, the remaining hardening solvent, such as copper and magnesium, available in the aluminum matrix for subsequent hardening is very limited. Although an alloy may contain 3 to 4% copper in its nominal composition, most of the copper combines with other elements to form intermetallic phases. Without solution treatment, these copper-containing intermetallic phases will not contribute to the hardening of the material.Therefore, adding Cu to current HPDC alloys used in production is not effective in terms of both improving properties and ensuring quality.

[0009] Typical high-performance direct conversion (HPDC) aluminum alloys are Al-Si-based alloys containing approximately 3 to 4% Cu. It is generally accepted that copper (Cu) has the single greatest influence of all dissolved alloying elements on the strength and hardness of aluminum alloy castings, both heat-treated and non-heat-treated, at both ambient and elevated operating temperatures. Copper is known to improve the machinability of alloys by increasing matrix hardness, thus facilitating the production of small cutting chips and fine machining finishes. On the other hand, Cu generally decreases the corrosion resistance of aluminum castings, and in certain alloys and mixtures, it increases susceptibility to stress corrosion cracking. Cu also increases the alloy freezing point and reduces feedability, resulting in a high potential for shrinkage porosity.

[0010] Furthermore, it has been reported that aluminum alloys with a high copper content (approximately 3 to 4%) have experienced unacceptable corrosion rates, particularly in saline environments. Typical high-pressure direct current (HPDC) aluminum alloys, such as A380 or 383, used for transmission and engine components, contain 2–4% copper. The corrosion problem with these alloys is expected to become more significant, especially with longer warranty periods and greater vehicle mileage requirements.

[0011] To address some of the known problems, aluminum alloys have been developed; however, the castings as a whole remain deficient. For example, the aluminum alloy A380 is a generally age-treatable alloy with the composition (in wt.%) 9 Si, 3.1 Cu, 0.86 Fe, 0.53 Zn, 0.16 Mn, 0.11 Ni, and 0.1 Mg (Lumley, RN et al., “Thermal characteristics of heat-treated aluminum high-pressure die-castings”, Scripta Materialia, 58 (2008), 1006–1009, the full disclosure of which is incorporated herein by reference). The developers teach that the Cu phases, for example, the Al₂Cu precipitate phase, are important for achieving the advantages of artificial age treatment and for improving the thermal conductivity of the casting. However, the castings suffer from lower corrosion resistance, a high potential for casting defects, and high material costs due to the percentage of copper.

[0012] It is known that reducing the copper content improves the corrosion resistance of an aluminum alloy material. However, copper is considered a necessary hardening component in HDPC aluminum castings. In a previously published paper, some of the researchers in the present application recommended a lower copper content in the range of 0.5 wt.% to 1.5 wt.%, depending on the as-cast conditions and heat treatment (see US application, serial number 12 / 827564, publication number US 2012 / 0000578A1, the entire disclosure of which is incorporated herein by reference). Nevertheless, the presence of copper in the casting solution after hardening was considered to preserve acceptable mechanical properties, particularly hardness / yield strength, of the casting.

[0013] In this field, Cu-free alloys, for example A356, are essentially known; however, they are typically used in other processes of sand foot and / or semi-permanent mold casting than HDPC, and as formulated, they suffer from the aforementioned deficiencies in mechanical properties, for example, poor tensile strength.

[0014] Lin (US patent application serial number 11 / 031,095, publication number US 2005 / 0167012A1) discloses an aluminum alloy with a reduced copper percentage; however, Lin still teaches the importance of the presence of some copper for the hardening process. Furthermore, Lin's alloy formulations and castings contain small weight percentages of silicon to avoid brittle eutectic Al-Si networks in the cast state. Lin's goal was to produce aluminum alloys suitable for thixoforming, a forming process that combines the features of casting and forging, involving low-pressure forming to produce particulate microcrystalline structures and avoiding solution heat treatment. Lin's alloys would be unsuitable for high-pressure direct deposition (HPDC) processes.

[0015] US 2012 / 0027639A1 relates to an alloy for use in die casting containing at least about 86.0 wt.% aluminum, about 9.70 to about 10.70 wt.% silicon, about 0.40 to about 0.70 wt.% iron, about 0.25 wt.% copper, about 0.50 wt.% manganese, about 0.10 to about 0.20 wt.% titanium; and about 0.010 to about 0.025 wt.% strontium.

[0016] US 2009 / 0038720A1 describes a heat treatment process for a casting made of an age-hardenable aluminum alloy produced by high-pressure die casting, which may exhibit blister-forming porosity in the as-cast condition, comprising the following steps: solution treatment of the casting by heating the casting to and within a temperature range in which dissolved elements can be dissolved into solid solution. The casting is then cooled to terminate the solution treatment by quenching the casting to a temperature below 100°C. The cooled casting is maintained within a temperature range that permits natural and / or artificial aging.

[0017] US 2002 / 0106301A1 relates to an aluminum-based die-casting alloy that is claimed to have improved corrosion resistance and good die-casting properties and contains about 4.5 to about 12 wt.% silicon, at least 87 wt.% aluminum, and at most 0.2 wt.% copper. The alloys preferably contain iron in an amount sufficient to improve hot tensile strength and reduce the tendency for the mold to stick or braze during die casting.

[0018] US 2003 / 0180178A1 describes a product comprising an ADC12 aluminum alloy, wherein the ADC12 aluminum alloy is cast into the product using a high-pressure, slow-speed casting technique. The alloy contains 1.5 to 3.5 wt.% copper, whereas conventional aluminum alloys also contain copper, in the range of 0.1 and 0.25 wt.%, respectively.

[0019] In this field, there is clearly a need for an aluminum alloy that is suitable for HPDC and amenable to hardening without compromising the corrosion resistance or mechanical properties of the cast components. SUMMARY OF THE INVENTION

[0020] Accordingly, the present disclosure essentially provides copper-free aluminum alloys suitable for high-pressure casting and aging at elevated temperatures with reduced porosity compared to known HPDC aluminum alloys. The castings exhibit improved mechanical properties for construction applications at both room temperature and elevated temperatures.

[0021] An aluminum alloy according to the invention is suitable for high-pressure casting processes and is capable of hardening, which provides superior mechanical properties after hardening at elevated temperatures. An aluminum alloy according to the invention, suitable for high-pressure casting and capable of hardening at elevated temperatures, contains at least 84 wt. percent aluminum (Al); 9.5 to 13 wt. percent silicon (Si); 0.2 to 0.6 wt. percent magnesium (Mg); and further comprises 0.1 to 2 wt. percent iron (Fe); 0.1 to 2 wt. percent manganese (Mn); wherein the wt. percent ratio Mn:Fe is 0.5 to 3 and the total amount of Mn + Fe is 0.5 to 2.0 wt. percent; and the alloy is substantially free of copper (Cu), wherein the copper content is < 0.01 wt. percent. and the alloy exhibits a eutectic phase in the range of 15-16 volume percent and hardening occurs in a temperature range of 500 °C to 650 °C.If the alloy is formulated with more than approximately 1 wt% Fe, then the alloy should preferably also include strontium (Sr). An alloy according to the disclosure may also include 1 wt% nickel (Ni) and 0.5 to 3.0 wt% zinc (Zn). The above composition ranges can be adjusted based on the performance requirements.

[0022] Other embodiments are directed towards HPDC castings made of an aluminum alloy according to the invention. An aluminum alloy according to the invention is formulated such that the alloy has a eutectic phase in the range of 15-16 volume percent and work hardening occurs over a relatively narrow temperature range compared to known HPDC aluminum alloys. Embodiments directed towards castings possess superior mechanical properties when hardened, for example under one of the T4, T5, T6 and T7 tempering treatment protocols.

[0023] Further embodiments are directed to methods for producing products from an aluminum alloy according to the invention by HDPC. These methods include providing a molten aluminum alloy according to embodiments of the invention, injecting the molten aluminum alloy into a mold under high pressure, allowing the alloy to solidify in the mold to form the casting, cooling the casting in the mold to a quenching temperature, quenching the casting in a quenching solution, and subjecting the casting to one or more hardening treatments. The alloy is formulated such that the casting solidifies in a temperature range of approximately 500 °C to approximately 650 °C and is hardened such that the casting has a eutectic phase in the range of 15-16 percent by volume.

[0024] These and other aspects and embodiments will be more clearly understood in light of the detailed description and figures shown below. BRIEF DESCRIPTION OF THE FIGURES

[0025] The following detailed description of specific embodiments can best be understood when read in conjunction with the following drawings: Fig. Figure 1 represents a typical T6 and / or T7 tempering treatment cycle for an aluminum alloy. Fig. Figure 2 is a graphical representation of the hardening responses of aluminium casting alloys A356 / A357, hardened at 70 °C, according to the state of the art. Fig. Figure 3 provides a calculated phase diagram of an aluminium casting alloy known in the field (A380-HPDC alloy) showing phase transformations as a function of copper content. Fig. Figure 4 provides a table comparing prior art aluminium casting alloy A380 with exemplary casting alloys according to specific embodiments of the invention. Fig. Figure 5 is a comparison of microscopic images of a tensile specimen of the A380 alloy showing porosity (block) in the middle part of the specimen and a tensile specimen of an embodiment E6 according to the invention showing no porosity in the middle part of the specimen. Fig. Figure 6 is a comparison of microscopic images of tensile specimens made of A380 alloy and an alloy embodiment according to the invention after immersion of both specimens in 3.5% NaCl solution for 240 h. Fig. Figure 7 presents empirical data and graphical representations comparing tensile properties, corrosion resistance, and corrosion conductivity in samples taken from T5-HDPC alloys A380, A360, and a specific embodiment E3 according to the invention. Figure 7A is a table of tensile data (T5) comparing tensile specimens taken from HDPC castings made of A380 and A360; Figure 7B presents a graphical representation of the corrosion current density of three samples; and Figure 7C presents a graphical representation of the corrosion rate of the three samples. Fig. Figure 8 provides a table of empirical data comparing the tensile properties of raw cast and T5-hardened HDPC samples cast from the known alloy A380 and six specific alloy formulations according to the invention. Fig. Figure 9 is a comparison of microscopic images showing the microstructures of a T5-cured HDPC product cast from the exemplary HDPC alloy A380 and a T5-cured HDPC product cast from a specific alloy E6 according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] Embodiments of the disclosure generally relate to substantially copper-free aluminum alloys formulated to provide high-temperature tempered cast components capable of annealing at elevated temperatures, exhibiting superior mechanical properties and reduced porosity. Unlike aluminum-based, copper-containing alloy castings known in the field, the present castings are suitable for a full range of temper hardening treatments.

[0027] As used herein, “castings” generally refers to high-pressure cast aluminum alloy parts formed by the work hardening of aluminum alloy compositions. The term “castings” may refer to any stage of a high-pressure casting process and / or a heat treatment process following work hardening, whether by cooling, quenching, tempering, or otherwise. Furthermore, “castings” may comprise any part, component, or product formed by any embodiment of the present invention.

[0028] Furthermore, “mechanical property” and related formulations thereof, as used herein, generally refer to at least one and / or a combination of strength, hardness, toughness, elasticity, plasticity, brittleness, ductility, and malleability that describes how a metal, for example, aluminum and alloys thereof, behaves under a load. Mechanical properties are generally described as the types of force or stress that the metal must withstand and how it withstands them.

[0029] "Strength," as used herein, means at least one of and / or any combination of yield strength, tensile strength, fatigue strength, and impact strength. Strength generally refers to a property that enables a material to resist deformation under a force or load. Yield strength generally refers to the stress at which a material begins to deform plastically. In engineering, the yield strength may be defined as the stress at which a predetermined amount (for example, about 2%) of permanent deformation occurs. Ultimate strength (UTS) generally refers to the maximum elongation a metal can withstand. Tensile strength generally refers to a measurement of the resistance to being pulled apart when placed under tensile load.Fatigue resistance generally refers to a metal's ability to withstand various types of rapidly changing stresses and can be expressed by the magnitude of the alternating stress for a specified number of cycles. Impact strength generally refers to a metal's ability to withstand suddenly applied forces. Generally, the yield strength is higher the higher the other strength properties are.

[0030] "Hardness," as used here, generally refers to a metal's property of resisting permanent indentation. Hardness is generally directly proportional to strength. Thus, a metal with high strength typically also has high hardness.

[0031] Aluminum alloy compositions that are work-hardened to form castings are known to include a number of elements, for example, but not limited to, aluminum (Al), silicon (Si), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), nickel (Ni), titanium (Ti), strontium (Sr), etc. The elements and their respective concentrations that define an aluminum alloy composition can significantly influence the mechanical properties of the resulting casting. Some elements, in particular, can be described as hardening solutes. These hardening solutes can interact with and / or bond to each other and / or with other elements during work-hardening, cooling, quenching, and aging of the casting, as well as during heat treatment processes. Ageing is generally used to increase the strength of the castings.While various hardening processes are available, for the reasons described above, only a few are applicable and / or sufficiently effective for high-pressure casting of aluminum alloys. Aluminum alloy castings produced using high-pressure casting are generally limited to T5 temper treatment (natural or artificial). Hardening increases the strength of castings by facilitating the precipitation of the hardening solvents in the aluminum alloy composition.

[0032] Artificial hardening (T5) heats the castings to an elevated, typically moderate, temperature for a sufficiently long time to increase the casting's strength through precipitation of the hardening solutes. Since precipitation is a kinetic process, the respective concentrations (supersaturation) of the hardening solutes available for precipitation are significant for the casting's strength response to hardening. Thus, the concentrations of hardening solutes and their availability for precipitation significantly influence the extent to which the casting hardens during hardening. If the hardening solutes are prevented, or substantially prevented, from bonding to one another and / or combining with other elements prior to hardening, then the hardening solutes may harden during hardening.Increased strength of the casting will precipitate.

[0033] To prevent, or at least substantially prevent, the hardening solutes from bonding to one another and / or combining with other elements of the aluminum alloy composition before hardening, and thereby to maintain the availability of the hardening solutes, the casting is cooled to a quenching temperature in the mold and quenched immediately thereafter. To facilitate the cooling of the casting to the quenching temperature, one embodiment may include selectively heating and / or cooling a specific area or several specific areas of the casting before its removal from the mold for quenching.

[0034] To increase precipitation during hardening and thereby improve the mechanical properties of the castings, one or more specific hardening solutes can be incorporated into the aluminum alloy composition. It is traditionally recognized in the field that magnesium (Mg), copper (Cu), and silicon (Si) are particularly effective and even necessary as hardening solutes in aluminum alloys. Mg can combine with Si to form Mg / Si precipitates, for example, β''-, β'-, and equilibrium Mg₂Si phases. The types, sizes, and concentrations of the precipitates typically depend on the prevailing hardening conditions and the composition of the aluminum alloys. For example, underhardening tends to form shearable β''-precipitates, while peak hardening and overhardening generally form non-shearable β'- and equilibrium Mg₂Si phases.When aluminum alloys are hardened, silicon (Si) can form silicon precipitates on its own. However, silicon precipitates are generally not as effective as magnesium / silicon precipitates in work hardening aluminum alloys. Furthermore, copper (Cu) can combine with aluminum (Al) to form multiple metastable precipitate phases, such as θ' ​​and θ, in Al-Si-Mg-Cu alloys, which are known to be very effective in work hardening and increasing strength.

[0035] It is also widely accepted that increased concentrations of the more effective hardening solutes can be incorporated into the aluminum alloy composition to increase their availability for precipitation during aging. According to specifications for conventional aluminum alloy compositions for HPDC, the maximum Mg concentration incorporated is generally less than 0.1 wt% of the respective compositions. However, in industrial practice, the Mg concentrations in such aluminum alloy compositions tend to be much lower than 0.1%. As a result, the compositions generally lack the capacity to form Mg / Si precipitates, resulting in minimal strength gains in the casting through Mg / Si precipitation, even during T5 aging processes.Indeed, it is generally accepted that the only feasible increase in the strength of the casting in this case results from the formation of Al / Cu precipitates. Cu is therefore considered a necessary hardening solvent in aluminum-silicon alloys in HPDC processes.

[0036] However, when an HPDC casting undergoes desired tempering treatments, the tempering effectiveness and contribution of copper can be surprisingly limited. Although typical HPDC aluminum alloys, for example A380, 380, or 383, contain 3–4% copper in their nominal composition, the actual dissolved copper content remaining in a raw cast aluminum matrix for subsequent tempering is significantly reduced. As in Fig. As shown in Figure 3, the copper content in the aluminum matrix is ​​only about 0.006%, even when the casting is quenched at approximately 200°C. Most of the copper is tightly bonded during work hardening with iron and other elements forming intermetallic phases, which do not exhibit any hardening responses unless the components / parts undergo high-temperature solution treatment. In this case, the role of the copper-containing intermetallic phases in stress hardening is similar to that of other second-phase particles such as silicon. The contribution of copper to hardening is, in fact, negligible.In contrast to the conventional view of the importance of Cu as a hardening dissolved substance, the inventors of the present invention surprisingly discovered that Cu can be removed from the alloy if the composition is formulated differently within certain parameters, in order to obtain essentially Cu-free aluminum alloys, where the copper content is < 0.01 wt.%, which provide HPDC castings with greater corrosion resistance and some superior mechanical properties.

[0037] Accordingly, one embodiment of the invention provides an aluminum alloy suitable for HPDC processes and capable of temper hardening at elevated temperatures. The alloy comprises at least 84 wt.% aluminum (Al); 9.5 to 13 wt.% silicon (Si); 0.2 to 0.6 wt.% magnesium (Mg) and is essentially free of copper (Cu), with a copper content of < 0.01 wt.%. Mg and Si are effective hardening solvents. Mg combines with Si to form Mg / Si precipitates, for example, β''-, β'-, and equilibrium Mg₂Si phases. The actual precipitate type, quantity, and size depend on the hardening conditions and, in particular, on the Mg and Si content remaining in the matrix after casting. Compared with Cu, the solubility of Si and Mg in the aluminum matrix is ​​higher. In the aluminum matrix, the spreading capacity of Mg and Si is also higher than that of Cu.An increase in silicon (Si) close to the eutectic composition (~12%) can help reduce the freezing point and thus improve castability and casting quality. Magnesium (Mg) and silicon (Si) are both lighter and less expensive than copper (Cu).

[0038] Ideally, a copper-free aluminum alloy should produce a similar amount of secondary phase particles in its microstructure after work hardening. The alloy should contain iron (Fe) to prevent tool brazing. However, Fe can readily form an undesirable needle-shaped intermetallic phase if manganese (Mn) is not added in appropriately proportional amounts. It is suggested that the ratio of Mn to Fe should be greater than 0.5.

[0039] According to other embodiments, the aluminum alloy further comprises: 0.1 to 2 wt.% Fe; 0.1 to 2 wt.% Mn; wherein the wt. percent ratio Mn:Fe is 0.5 to 3 and the total amount of Mn + Fe is 0.5 to 1.5 wt.%. Preferably, the total amount of Mn + Fe is less than 1.5 wt.%. In more specific embodiments, the wt. percent ratio Mn:Fe is between 1.0 and 2, and the total amount of Mn + Fe is 0.8 to 1.2%. If the alloy comprises a wt. percent content of Fe greater than 1.0, then the alloy should also comprise strontium (Sr) at about 500 ppm. In other specific embodiments, the alloy further comprises 0.1 to 1 wt.% nickel (Ni); 0.5 to 3.0 wt.% zinc (Zn); and 0 to 0.1 wt.% strontium (Sr). According to a very specific embodiment, an aluminum alloy suitable for HPDC and capable of hardening consists essentially of: at least 84 to 90 wt.% aluminum (Al); 9.5 to 13 wt.%-% Si; 0.2 to 0.6 wt% Mg; 0.1 to 2 wt% Fe; 0.1 to 2 wt% Mn; 0.1 to 1 wt% Ni; 0.5 to 3.0 wt% Zn and 0 to 0.1 wt% Sr. In a more specific form.

[0040] In this embodiment, the aluminum alloy consists essentially of: 11 wt.% Si; 0.4 wt.% Mg; 1.0 wt.% Fe; 0.8 to 1.0 wt.% Mn; 0.3 wt.% Ni; 2.0 wt.% Zn and Al as the remainder. The amount of all other trace elements should not exceed 0.25 wt.% of the alloy.

[0041] Table 1 of Fig. Figure 4 provides a comparison of the calculated amount of second-phase particles and the hardening-freeze range between two typical specific embodiments according to the invention and the conventional A380-HPDC alloy. Remarkably, the typical alloys according to the invention have similar amounts of eutectic phase particles after hardening; however, the hardening range drops to close to 60 °C, which is desirable for casting quality (low shrinkage porosity). Therefore, an aluminum alloy according to the invention will have similar tensile properties to A380 in the as-cast condition but will possess superior properties after T5 tempering. According to some embodiments, a substantially Cu-free aluminum casting according to the disclosure is hardened after T5 or T6 / T7 tempering and exhibits a eutectic phase in the range of 15 to 16 volume percent.

[0042] What Fig. Regarding point 5, microscopic images of samples of A380 alloy (top) and an alloy E6 according to the invention (bottom) are shown for comparison. The tensile test specimen of A380 alloy shows porosity (block) in the central part of the sample, whereas a tensile test specimen of a specific embodiment of E6 shows almost no porosity in the central part of the sample. The ability to harden at elevated temperatures with reduced porosity provides castings with superior mechanical properties, specifically suited for applications in the automotive industry.

[0043] As seen through the microscopic images, which are considered Fig. As is clear from Figure 6, castings made from alloys according to the invention possess superior corrosion resistance compared to the prior art HPDC alloy A380. A significant benefit achieved by the alloys according to the invention is that the corrosion problems known in the field to be associated with a copper content can be eliminated without compromising the strength of the HPDC casting. Fig. Figure 7 illustrates this point in more detail. Figure 7A is a tabulated comparison of data generated in an experiment investigating and comparing HDPC castings made from known HDPC A380 and A360 alloys and the specific alloy formulation E3 according to the invention. The castings were subjected to T5 hardening. Compositions, tensile properties of the castings, and corrosion conductivity data are all listed for comparison purposes. The corrosion conductivity is shown in Figure 7A. Fig. 7B and Fig. Figure 7C is also shown graphically. An examination of the data shows that E3, which does not contain Cu, has much better corrosion resistance compared to existing HPDC alloys, of which A380 and A360 are examples. Furthermore, E3 has at least similar tensile properties in the as-cast condition, but a better hardening response and thus higher tensile strength after T5 heat treatment compared to the exemplary HDPC alloys A380 and A360. Remarkably, the alloy according to the invention is also somewhat lighter, which provides an additional cost-benefit advantage.

[0044] Fig. Figure 8 presents empirical data in tabular form for two experimental groups comparing the tensile properties of crudely cast HDPC specimens and T5-hardened specimens cast from the known alloy A380 and six specific alloy formulations according to the invention. The tensile specimens were produced in a permanent mold (PM mold) with a measuring diameter of 12.7 mm. The first group of experimental results indicates that castings made from specific alloy compositions E1-E3 according to the invention possess at least equivalent or better mechanical properties, both crudely cast and after T5 hardening, than the A380 alloy in PM mold castings. The second group of experimental results indicates that castings made from specific alloy formulations E4-E6 according to the invention also possess at least equivalent or better mechanical properties, both crudely cast and after T5 hardening, than the A380 alloy in a permanent mold (PM) casting.

[0045] According to another embodiment, an HPDC casting is provided, cast from a substantially copper-free aluminum alloy formulated according to the disclosure. Unlike conventional copper-containing alloys, the copper-free alloy can undergo effective T4, T5, or T6 / T7 tempering treatments. In specific embodiments, the casting is tempered at T4 tempering treatment temperatures of at least 500 °C. The casting can have a microstructure comprising at least one or more insoluble solidified and / or precipitated particles with at least one alloying element selected from the group consisting of Al, Si, Mg, Fe, Mn, Zn, Ni, and Sr. As described by Fig.As demonstrated in Figure 9, the microstructure of an exemplary known Cu-containing HDPC alloy, A380, contains large eutectic particles after T5 curing conditions, whereas the microstructure of an exemplary alloy according to embodiments of the invention, E6, has smaller eutectic particles. Remarkably, the crudely cast E6 product exhibits an equivalent volume fraction of eutectic particles as A380, but has a much narrower freezing range, which is beneficial for the casting quality.

[0046] According to other embodiments, an HPDC manufacturing process is provided in which a molten, substantially copper-free aluminum alloy is provided and poured under high pressure into a die. The alloy solidifies in the die to form the casting, and the casting is cooled in the die to a desired quenching temperature, which is generally determined empirically. The casting can be removed from the die and quenched in a quenching solution. The casting can be subjected to one or more tempering treatments, including T4 (solution heat-treated and ambient-cured), T5 (cooled and then artificially cured at elevated temperatures), T6 (solution heat-treated and artificially cured at elevated temperatures), and T7 (solution heat-treated and stabilized).In specific embodiments of the process, a casting solidifies according to the disclosure at a temperature of approximately 500 °C to approximately 650 °C and exhibits a eutectic phase in the range of 15 to 16 volume percent. In specific embodiments, the casting solidifies at a temperature above 500 °C within a temperature range of less than 140 °C.

[0047] According to very specific embodiments, the method for producing a high-pressure die-cast part from an aluminum alloy comprises: providing a molten aluminum alloy consisting essentially of at least 84 to 90 wt. percent aluminum (Al), 9.5 to 13 wt. percent silicon (Si), 0.2 to 0.6 wt. percent magnesium (Mg), 0.1 to 2 wt. percent iron (Fe), 0.1 to 2 wt. percent manganese (Mn), 0.1 to 1 wt. percent nickel (Ni), 0.5 to 3.0 wt. percent zinc (Zn) and 0 to 0.1 wt. percent strontium (Sr) and wherein the alloy is essentially free of copper (Cu), wherein the copper content is < 0.01 wt.% is; Casting the molten aluminum alloy into a mold under high pressure; Allowing the alloy to solidify in the mold to form the molded part; Cooling the molded part in the mold to a quenching temperature; Quenching the casting in a quenching solution and subjecting the casting to a T5 hardening treatment, whereby the casting has a eutectic phase in the range of 15-16 volume percent and hardens in a temperature range of 500 °C to 650 °C.

[0048] It should be noted that terms such as "generally", "conventionally", and "typically", when used herein, are not intended to limit the scope of protection of the claimed embodiments or to imply that certain features are critical, essential, or even important to the structure or function of the claimed embodiments. Rather, these terms are merely intended to identify certain aspects of an embodiment or to highlight alternative or additional features that may or may not be used in a particular embodiment.

[0049] For the purposes of describing and defining embodiments, it should be noted that the terms "essentially," "significantly," and "approximately" are used here to indicate the inherent degree of uncertainty present in any quantitative comparison, value, measurement, or other representation. The terms "essentially," "significantly," and "approximately" are also used here to indicate the degree to which a quantitative representation may deviate from a given reference without altering the fundamental function of the object in question.

[0050] Having described embodiments of the present invention in detail and / or by reference to specific embodiments herein, it will be obvious that modifications and variations are possible without departing from the scope of the embodiments defined in the appended claims. Although some aspects of embodiments of the present invention have been identified here as preferred or particularly advantageous, it should be noted that the embodiments of the present invention are not necessarily limited to these preferred aspects.

Claims

[1] Aluminium alloy suitable for high-pressure casting and capable of hardening at elevated temperatures, the alloy comprising: at least 84 percent by weight of aluminium (Al); 9.5 to 13 percent by weight silicon (Si); 0.2 to 0.6 percent by weight of magnesium (Mg); and also 0.1 to 2 percent by weight of iron (Fe); Contains 0.1 to 2 percent by weight of manganese (Mn); where the weight percent ratio Mn:Fe is 0.5 to 3 and the total amount of Mn + Fe is 0.5 to 2.0 weight percent; and the alloy is essentially free of copper (Cu), with the copper content being < 0.01 percent by weight; and The alloy exhibits a eutectic phase in the range of 15-16 volume percent and hardening occurs in a temperature range of 500 °C to 650 °C. [2] Alloy according to claim 1, wherein the total amount of Mn + Fe is less than 1.5 percent by weight. [3] Alloy according to claim 1, wherein the weight percent ratio Mn:Fe is between 1.0 and 2 and the total amount of Mn + Fe is 0.8 to 1.2 weight percent. [4] Alloy according to any of the preceding claims, wherein, if the weight percent of Fe is greater than 1.0, the alloy also comprises strontium (Sr). [5] Alloy according to any of the preceding claims, further comprising 0.1 to 1 percent by weight of nickel (Ni); 0.5 to 3.0 percent by weight zinc (Zn) and Contains 0 to 0.1 percent by weight of strontium (Sr). [6] Aluminium alloy suitable for high-pressure casting and capable of hardening, wherein the alloy consists of: at least 84 to 90 percent by weight of aluminium (Al); 9.5 to 13 percent by weight silicon (Si); 0.2 to 0.6 percent by weight of magnesium (Mg); 0.1 to 2 percent by weight of iron (Fe); 0.1 to 2 percent by weight of manganese (Mn); 0.1 to 1 percent by weight of nickel (Ni); 0.5 to 3.0 percent by weight zinc (Zn) and 0 to 0.1 percent by weight strontium (Sr) consists and wherein the alloy is essentially free of copper (Cu), the copper content being < 0.01 wt%, and has a eutectic phase in the range of 15 to 16 vol%. [7] High-pressure cast product cast from an aluminium alloy according to claim 1. [8] Casting product according to claim 7, which has been subjected to annealing at elevated temperature, wherein the annealing conditions comprise one of the temper treatments T4, T5, T6 and / or T7 and the casting product has been annealed in a T4 temper treatment at at least 500 °C. [9] Cast product according to claim 7, which has been subjected to tempering at elevated temperature, wherein the product has been tempered by temper treatment T6 / T7 and has a eutectic phase in the range of 15-16 volume percent. [10] A method for producing a high-pressure cast part from an aluminum alloy, the method comprising: providing a molten aluminum alloy consisting of at least 84-90 wt% aluminum (Al), 9.5 to 13 wt% silicon (Si), 0.2 to 0.6 wt% magnesium (Mg), 0.1 to 2 wt% iron (Fe), 0.1 to 2 wt% manganese (Mn), 0.1 to 1 wt% nickel (Ni), 0.5 to 3.0 wt% zinc (Zn) and 0 to 0.1 wt% strontium (Sr), wherein the alloy is substantially free of copper (Cu), the copper content being < 0.01 wt%; pouring the molten aluminum alloy into a die under high pressure; allowing the alloy to solidify in the die to form the casting; cooling the casting, still in the die, to a quenching temperature;Quenching the casting in a quenching solution and subjecting the casting to a T5 hardening treatment, wherein the casting has a eutectic phase in the range of 15-16 volume percent and solidifies in a temperature range of 500 °C to 650 °C.

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