US20170107599A1

US20170107599A1 - New high pressure die casting aluminum alloy for high temperature and corrosive applications

Info

Publication number: US20170107599A1
Application number: US14/886,263
Authority: US
Inventors: Qigui Wang; Wenying Yang; Bing Ye
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2015-10-19
Filing date: 2015-10-19
Publication date: 2017-04-20
Also published as: DE102016118729A1; DE102016118729B4; CN106591638A

Abstract

Copper-free aluminum alloys suitable for high pressure die casting and capable of age-hardening under elevated temperatures. The alloy includes about 7-15 wt % silicon, about 0 to 0.6 wt % magnesium, about 0 to 1.0 wt % iron, about 0 to 1.0 wt % manganese, about 0 to 1.0 wt % zinc, about 0 to 0.1 wt % strontium, about 0 to 0.5 wt % titanium, about 0 to 0.5 wt % zirconium, about 0 to 0.5 wt % vanadium, about 0 to 0.5 wt % copper, and about 0 to 1.0 wt % nickel, with a balance of aluminum. Methods for making high pressure die castings and castings manufactured from the alloy.

Description

FIELD OF THE INVENTION

The invention relates generally to a low copper (Cu) or Cu-free aluminum alloy formulated for high pressure die casting (HPDC), and the castings therefrom, which are capable of age-hardening at elevated temperatures with reduced porosity, thus possessing superior mechanical properties for applications particularly in the automotive industry.

BACKGROUND OF THE INVENTION

HPDC is a cost-effective and wide-spread method for industrial production of metal components requiring precise dimensional consistency, low dimensional tolerances and where a smooth surface finish is important. Manufacturers in the car industry are now increasingly required to produce near-net-shape aluminum components with a combination of high tensile properties and ductility, and HPDC affords the most economic production method for large-scale quantities of small to medium sized components.
In order to avoid discontinuities in the cast component, the molten alloy is injected into the die cavity rapidly enough that the entire cavity fills before any portion of the cavity begins to solidify. Hence, the injection is under high pressure and the molten metal is subject to turbulence as it is forced into a die and then rapidly solidifies. Unfortunately, since the air being replaced by the molten alloy has little time to escape, some of it is trapped and porosity results. Castings also contain pores resulting from gas vapor decomposition products of the organic die wall lubricants and porosity may also result from shrinkage during solidification. A major drawback of the porosity, particularly induced from entrapped air or gas vapor, resulting from the HPDC process is that castings made from aluminum alloys which ordinarily have the capacity to respond to age-hardening cannot be effectively artificially aged, that is, they cannot attain high supersaturation of hardening elements such as Mg or Cu in the solution prior to artificial aging because no traditional solution treatment can be applied to high pressure die casting parts. The internal pores containing gases or gas forming compounds in the high pressure die castings expand during conventional solution treatment at elevated temperatures, resulting in the formation of surface blisters on the castings. The presence of these blisters affects not only the appearance of castings but also dimensional stability and in some cases it can negatively impact particular mechanical properties of HPDC components. Specifically, aluminum alloy HPDC cast parts are not amenable to solution treatment (T4) at a high temperature, for example 500° C., which significantly reduces the potential of precipitation hardening through a full temper T6 and/or T7 (equivalently phrased as a combination of temper T4 and T5) heat treatment. As such, it is nearly impossible to find a conventionally processed HPDC component without large gas bubbles.
In Al—Si casting alloys (e.g., alloys 319, 356, 390, 360, 380), strengthening is achieved through heat treatment after casting, with addition of various alloying hardening solutes including, but not limited to, Cu and Mg. The heat treatment of cast aluminum involves a mechanism described as age hardening or precipitation strengthening. Heat treatment (conventional T6 and/or T7 heat treatment) generally includes at least one 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 to homogenize or modify the microstructure; (2) rapid cooling, or quenching into a cold or warm liquid medium after solution treatment, such as water, to retain the solute elements in a supersaturated solid solution; and (3 ) artificial aging (T5) by holding the alloy for a period of time at an intermediate temperature suitable for achieving hardening or strengthening through precipitation. Solution treatment (T4) serves three main purposes: (1) dissolution of elements that will later cause age hardening, (2) spherodization of undissolved constituents, and (3) homogenization of solute concentrations in the material. Quenching after T4 solution treatment retains the solute elements in a supersaturated solid solution (SSS) and also creates a supersaturation of vacancies that enhances the diffusion and the dispersion of the precipitates. To maximize the strength of the alloy, the precipitation of all strengthening phases should be prevented during quenching. Aging (T5, either natural or artificial aging) creates a controlled dispersion of strengthening precipitates.
With T5 aging, there generally are three types of aging conditions, which are commonly referred as underaging, peak aging and over aging. At pre-aging, or an initial stage of aging, Guinier-Preston (GP) zones and fine shearable precipitates form, and the casting is considered to be underaged. In this condition, mechanical properties of the casting, for example material hardness and yield strength, are usually low. Increased time at a given temperature or aging at a higher temperature further evolves the precipitate structure increasing mechanical properties such as hardness and yield strength to maximum levels for achieving the peak aging/hardness condition. Further aging decreases the hardness/yield strength and the casting becomes overaged due to precipitate coarsening and its transformation of crystallographic incoherency.
Considering that the conventional HPDC aluminum components inevitably contain internal porosity, artificial aging (T5) becomes a very important step in achieving the desired mechanical properties without causing blistering. The strengthening that results from aging occurs because the retained hardening solutes present in the supersaturated solid solution form precipitates that are finely dispersed throughout the grains and that increase the ability of the casting to resist deformation by slip and plastic flow. Maximum hardening or strengthening may occur when the aging treatment leads to the formation of a critical dispersion of at least one type of these fine precipitates.
In addition, in conventional HPDC processes the cast parts are often slowly cooled to a low temperature, for example, below 200° C., prior to die ejection and quench. This significantly diminishes the subsequent aging potential since the hardening solute solubility decreases significantly with decreasing quench temperature. As a result, the remaining hardening solute, such as Cu and Mg, available in the aluminum matrix for subsequent aging hardening is very limited. Although an alloy may contain 3˜4% Cu in nominal composition, most of the Cu combines with other elements to form intermetallic phases. Without solution treatment, the Cu-containing intermetallic phases will not contribute to age hardening of the material. Therefore, addition of Cu in the current HPDC alloys used in production is not effective in terms of both property improvement and quality assurance.
Typical Al—Si based HPDC alloys contain about 3˜4% Cu. It is generally accepted that copper (Cu) has the single greatest impact of all alloying solutes/elements on the strength and hardness of aluminum alloy castings, both heat-treated and not heat-treated and at both ambient and elevated service temperatures. Cu is known to improve the machinability of alloys by increasing matrix hardness, making it easier to generate small cutting chips and fine machined finishes. On the downside, Cu increases the alloy freezing range and decreases feeding capability, leading to a high potential for shrinkage porosity. More significantly, it generally reduces the corrosion resistance of aluminum castings; and in certain alloys and tempers, it increases stress corrosion susceptibility. For example, it has been reported that aluminum alloys with a high Cu content (i.e., above about 3-4%) have experienced an unacceptable rate of corrosion, especially in salt-containing environments. Typical high pressure die (HPDC) aluminum alloys, such as A 380 or 383, which are used for transmission and engine parts, contain 2-4% Cu. It can be anticipated that the corrosion issue of these alloys will become more significant, particularly when longer warranty time and higher vehicle mileages are required.
Aluminum alloys have been developed to address some of the known problems. For example, Aluminum alloy A380 is a generally age-hardenable alloy with the composition (in wt. %) 9 Si, 3.1 Cu, 0.86 Fe, 0.53 Zn, 0.16 Mn, 0.11 Ni and 0.11 Mg (Lumley, R.N. et al. “Thermal characteristics of heat-treated aluminum high-pressure die-castings” 1 Scripta Materialia 58 (2008) 1006-1009, the entire disclosure of which is incorporated herein by this reference). It is known that the Cu-phases, such as the Al₂Cu precipitate phase, are important to achieving the benefits of artificial aging, as well as for improving thermal conductivity of the casted part. However the castings suffer from lower corrosion resistance, a high potential for cast defects and a high material cost due to the Cu.
It is known that reducing the Cu content improves the corrosion resistance of an aluminum alloyed material. However Cu is thought to be a necessary hardening component in HPDC aluminum castings. In previously published work, some of the present inventors recommended lower Cu content ranges of 0.5% to 1.5% by weight depending upon the as-cast and heat treatment conditions (see U.S. application Ser. No.12/827,564, publication No. 20120000578, the entire disclosure of which is incorporated herein by this reference). Nonetheless the presence of Cu in the casting solution after solidification was considered integral to the preservation of acceptable mechanical properties, in particular hardness/yield strength of the cast.
Essentially Cu-free alloys, such as A356, are known in the art, however they are typically used in sand casting and/or semi-permanent mold casting processes other than HPDC and as formulated, suffer from deficiencies in mechanical properties such as tensile strength.
Lin (U.S. patent application Ser. No. 11/031,095) discloses an aluminum alloy having reduced a reduced Cu percentage; however Lin nonetheless teaches the importance of presence of some Cu to the hardening process. Moreover, the Lin alloy formulations and castings contain low weight percentages of Si in order to avoid brittle Al—Si eutectic networks in the casted condition. The goal of Lin was to produce aluminum alloys suitable for thixoforming, a molding process which combines features of casting and forging involving low- pressure molding to produce particular microcrystalline structures and to avoid solution heat treatment. The alloys of Lin would be unsuitable for HPDC methods.
Clearly a need exists in the art for an aluminum alloy suitable for HPDC and amenable to age hardening, without compromising corrosion resistance or mechanical properties of the cast components.

SUMMARY OF THE INVENTION

Accordingly, the present disclosure provides substantially Cu-free or low-Cu aluminum alloys suitable for high pressure die casting and age-hardening at elevated temperatures with reduced porosity compared to known HPDC aluminum alloys. The castings exhibit enhanced mechanical properties for both room and elevated temperature structural applications.
An aluminum alloy according to invention is suitable for high pressure die casting processes and is capable of age hardening, providing superior mechanical properties after age hardening at elevated temperatures. Embodiments of the aluminum alloy comprise by weight about 7 to about 15% silicon (Si); about 0 to about 0.6% magnesium (Mg); about 0 to about 1% iron (Fe); about 0 to about 1% manganese (Mn); about 0 to about 1.0% zinc (Zn); about 0 to about 0.1 weight percent strontium (Sr); about 0 to about 0.5 weight percent titanium (Ti); and about 0 to about 0.5% zirconium (Zr) and at least about 78% aluminum. An alloy may further comprise about 0 to about 0.5% vanadium (V). An alloy according to the disclosure may also include about 0 to about 0.5% copper (Cu); and about 0 to about 1% nickel (Ni). The above composition ranges may be adjusted based on performance requirements.
Other embodiments are directed to HPDC articles cast from an aluminum alloy according to the invention. An aluminum alloy is formulated such that the alloy exhibits corrosion of less than about 0.1 millimeter per year. An aluminum alloy is formulated such that the alloy being as-cast, age-hardened by temper T5 treatment, and soaked at 200° C. for 200 hours and tested at 200° C. exhibits a yield strength above about 150 MPa, ultimate tensile strength above about 190 MPa, and strain above about 1.8 percent. The alloy is capable of receiving solution treatment over a period generally less than what other aluminum alloys require. These embodiments would not experience blistering, and would be able to undergo effective temper or T6/T7 age-hardening treatments. Embodiments directed to cast articles possess superior mechanical properties when subjected to one or more steps of age-hardening temper treatments.
Further embodiments are directed to methods for manufacturing articles by HPDC of an aluminum alloy according to the invention. The methods comprise providing a molten aluminum alloy according to embodiments of the invention, injecting the molten aluminum alloy into a die under high pressure, solidifying the alloy in the die to form the casting, cooling the casting in the die to a quenching temperature, quenching the casting in a quenching solution, and subjecting the casting to one or more age-hardening treatments. The alloy is formulated such that the casting corrodes at a rate of less than about 0.1 millimeter per year and maintains a yield strength above about 150 MPa, ultimate tensile strength above about 190 MPa, and strain above about 1.8 percent after it is soaked at 200° C. for 200 hours and tested at 200° C.
These and additional aspects and embodiments will be more clearly understood in view of the detailed description and figures set forth below.

BRIEF DESCRIPTION OF THE FIGURES

The following detailed description of specific embodiments can be best understood when read in conjunction with the following drawings:

FIG. 1. sets forth a calculated phase diagram of a cast aluminum alloy known in the art (A380 HPDC alloy) showing phase transformations as a function of Cu content.

FIG. 2. sets forth a chart displaying the porosity increases of the present work in relation to the Cu level according to a specific embodiments of the invention.

FIG. 3. sets forth empirical data comparing the chemical composition of T5 HPDC alloys A380, A360 and an embodiment according to the invention comparing tensile properties and corrosion resistance and corrosion conductivity in samples taken from.

FIG. 4. sets forth tabled empirical data comparing tensile properties in as-cast, T5-aged, and soaked HPDC samples cast from known alloy A360, A380, and one specific alloy embodiment according to the invention.

FIG. 5. sets forth tabled empirical data comparing tensile properties in as-cast, T5-aged, and soaked HPDC samples cast from known alloy A360, A380, and another specific alloy embodiment according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the disclosure relate generally to substantially Cu-free or low-Cu aluminum alloys formulated to provide HPDC casted components capable of age-hardening at elevated temperatures and exhibiting superior mechanical properties and reduced porosity. Unlike aluminum-based Cu containing alloy castings known in the art, the present castings are capable of a full range of temper age-hardening treatments.
As used herein, “castings” refer generally to aluminum alloy high pressure die castings formed through solidification of aluminum alloy compositions. Thereby, the castings may be referred to herein during any stage of a high pressure die casting process and/or a heat treatment process subsequent to solidification, whether cooling, quenching, aging, or otherwise. Further, castings may include any part, component, product formed via an embodiment of the present invention.
Further, as used herein, “mechanical property,” and related phrases thereof, refer generally to at least one and/or any combination of, strength, hardness, toughness, elasticity, plasticity, brittleness, and ductility and malleability that measures how a metal, such as aluminum and alloys thereof, behaves under a load. Mechanical properties generally are described in terms of the types of force or stress that the metal must withstand and how these are resisted.
As used herein, “strength” refers to at least one and/or any combination of yield strength, ultimate strength, tensile strength, fatigue strength, and impact strength. Strength refers generally to a property that enables a metal to resist deformation under a load. Yield strength refers generally 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 instance about 0.2%) of permanent deformation occurs. Ultimate strength refers generally to a maximum strain a metal can withstand. Tensile strength refers generally to a measurement of a resistance to being pulled apart when placed in a tension load. Fatigue strength refers generally to an ability of a metal to resist various kinds of rapidly changing stresses and may be expressed by the magnitude of alternating stress for a specified number of cycles. Impact strength refers generally to the ability of a metal to resist suddenly applied loads. Generally, the higher the yield strength, the higher the other strengths are as well.
As used herein, “hardness” refers generally to a property of a metal to resist permanent indentation. Hardness generally is directly proportional to strength. Thus, a metal having a high strength also typically has high hardness.
Aluminum alloy compositions solidified to form castings are known to comprise a number of elements, such as, 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 may affect significantly the mechanical properties of the casting formed therefrom. More particularly, some elements may be referred to as hardening solutes. These hardening solutes may engage and/or bond among themselves and/or with other elements during solidification, cooling, quenching, and aging of casting and heat treatment processes. Aging generally is used to strengthen castings. While, various processes for aging are available, generally only some are applicable and/or sufficiently effective for aluminum alloy high pressure die casting processes, for reasons described above. Aluminum alloy castings known to the HPDC parts have generally been limited to temper T5 treatment aging (natural or artificial). Aging strengthens castings by facilitating the precipitation of the hardening solutes of the aluminum alloy composition.
Artificial aging (T5) heats the castings to an elevated, typically intermediate, temperature for a length of time sufficient to strengthen the casting 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 to the casting's strengthening response to aging. Therefore, the concentrations of hardening solutes, and the availability thereof for precipitation, significantly impact the extent to which the casting is strengthened during aging. If the hardening solutes are prevented, or substantially prevented, from bonding among themselves and/or with other elements prior to the aging, then the hardening solutes may precipitate during aging to strengthen the casting.
To prevent, or at least substantially prevent, the hardening solutes from bonding among themselves and/or with other elements of the aluminum alloy composition prior to aging and, thereby, maintain the availability of the hardening solutes, the casting is cooled to a quenching temperature in the die and quenched immediately thereafter. To facilitate the cooling of the casting to the quenching temperature, an embodiment may comprise selectively heating and/or cooling one or more designated areas of the casting prior to its removal from the die for quenching.
Further, to increase precipitation during aging, and, thereby, enhance mechanical properties of castings, one or more specific hardening solutes typically are incorporated into the aluminum alloy composition. Traditionally it has been accepted in the art that magnesium (Mg), copper (Cu), and silicon (Si) are particularly effective and even necessary as hardening solutes in aluminum alloys. Mg may combine with Si to form Mg/Si precipitates, such as β″, β′, and equilibrium Mg₂Si phases. The precipitate types, sizes, and concentrations typically depend on the present aging conditions and the compositions of the aluminum alloys. For example, under-aging tends to form shearable β″ precipitates, while peak-aging and over-aging generally form unshearable β′ and equilibrium Mg₂Si phases. When aging aluminum alloys, Si alone can form Si precipitates. Si precipitates, however, generally are not as effective as Mg/Si precipitates in strengthening aluminum alloys. Further, 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 strengthening.
It is also widely accepted that increased concentrations of the more effective hardening solutes may be incorporated into the aluminum alloy composition to increase their availability for precipitation at aging. According to specifications for conventional aluminum alloy compositions for HPDC, generally the maximum Mg concentration incorporated is less than 0.1% by weight of the respective compositions. In industry practice, however, the Mg concentrations in such aluminum alloy compositions tend to be much lower than 0.1%. As a result, the compositions generally have an inability to form Mg/Si precipitates and, as such, minimal strengthening of the casting through Mg/Si precipitation results, even during T5 aging processes. In fact, it is generally accepted that the only feasible strengthening of the casting in this case results through formation of Al/Cu precipitates. Cu, therefore, has been considered a necessary hardening solute in aluminum-silicon alloys in HPDC operations.
However, when subjecting an HPDC casting to desirable age-hardening temper treatments, the hardening efficacy and contribution of Cu may be surprisingly limited. Although typical HPDC aluminum alloys, such as A380, 380 or 383, contain 3˜4% Cu in nominal composition, the actual Cu solute remaining in as-cast aluminum matrix for the subsequent aging is actually much reduced. As shown in FIG. 1, the Cu content in the aluminum matrix is only about 0.006% even when the casting is quenched at about 200° C. A majority of the Cu is tied up during solidification with Fe and other elements forming intermetallic phases which have no aging responses if the components/parts do not undergo high temperature solution treatment. In this case, the role the Cu-containing intermetallic phases play in the strain-hardening is similar to other second phase particles like Si. The contribution of Cu to the aging hardening in the conventional high pressure die casting parts is actually negligible. Therefore, contrary to convention regarding the importance of Cu as a hardening solute, the present inventors discovered that Cu may be removed from the alloy if the composition is otherwise formulated within particular parameters to achieve substantially Cu-free aluminum alloys which provide HPDC castings with greater corrosion resistance, and some superior mechanical properties. Otherwise, small amounts of Cu may be utilized in the alloy to maintain some of the benefits it contributes. It should also be noted that Mg has high diffusivity in Al—Si alloy. Since the alloy only needs to diffuse Mg and Si particles in solution treatment, the solution treatment time can be shortened. The low-Cu and Cu-free embodiments discussed herein provide this advantage of shortened treatment time. This additionally allows for effective temper treatment or T6/T7 age-hardening treatments.
FIG. 2 depicts a chart comparing the volume fraction of porosity to the Cu level in an alloy according to one embodiment of the present invention. Also shown for the comparison are some data points from the work of prior art as is shown, the porosity increases significantly when Cu is between 0.5 and 0.8 weight percent. Within this range, the volume fraction of porosity increases from about 0.4 percent to about 0.6 percent. Above this range, the porosity levels around 0.7 percent. Below this range, the porosity also increases significantly, but is still within an expected range. The reduced porosity levels present when the Cu level is within the range anticipated by the present invention, from about 0 to about 0.5 weight percent, ensures the improved performance of the alloy.
Accordingly, one embodiment of the invention provides an aluminum alloy suitable for HPDC processes and capable of temper age-hardening at elevated temperatures. The alloy comprises at least about 78 weight percent aluminum (Al); about 7 to about 15 weight percent silicon (Si); about 0 to about 0.6 weight percent magnesium (Mg); about 0 to about 1 weight percent iron (Fe); about 0 to about 1 weight percent manganese (Mn); about 0 to about 1.0 weight percent zinc (Zn); about 0 to about 0.1 weight percent strontium (Sr); about 0 to about 0.5 weight percent titanium (Ti); and about 0 to about 0.5 weight percent zirconium (Zr). Mg and Si are effective hardening solutes. Mg combines with Si to form Mg/Si precipitates such as β″, β′ and equilibrium Mg₂Si phases. The actual precipitate type, amount, and sizes depend on aging conditions and particularly the Mg and Si content remained in the matrix after casting. Compared with Cu, the solubility of Si and Mg in aluminum matrix is higher. Also, the diffusivity of Mg and Si in the aluminum matrix is higher than Cu. Increasing Si near the eutectic composition (˜12%) can also help reduce freezing range and thus increase castability and quality of the casting. Mg and Si are both lighter and more cost-effective than Cu.
Ideally, a Cu-free aluminum alloy should produce a similar quantity of second phase particles in the microstructure after solidification. The alloy also should contain iron (Fe) to avoid die soldering. Fe, however, can easily form an undesirable needle-shape intermetallic phase if manganese (Mn) is not added in appropriately proportional amounts.
According to other embodiments, the aluminum alloy further comprises: about 0 to about 0.5 weight percent vanadium (V). According to a very specific embodiment, an aluminum alloy suitable for HPDC and capable of age-hardening consists essentially of: about 13 weight percent silicon (Si); about 0.4 weight percent magnesium (Mg); about 0.4 weight percent iron (Fe); about 0.8 weight percent manganese (Mn); about 0.5 weight percent zinc (Zn); about 0.04 weight percent strontium (Sr); about 0.3 weight percent titanium (Ti); about 0.15 weight percent zirconium (Zr); and a balance of aluminum (Al). According to another very specific embodiment, an aluminum alloy suitable for HPDC and capable of age-hardening consists essentially of: about 8.5 weight percent silicon (Si); about 0.4 weight percent magnesium (Mg); about 0.4 weight percent iron (Fe); about 0.5 weight percent manganese (Mn); about 0.5 weight percent zinc (Zn); about 0.04 weight percent strontium (Sr); about 0.3 weight percent titanium (Ti); about 0.3 weight percent zirconium (Zr); about 0.3 weight percent vanadium (V); and a balance of aluminum (Al). According to another very specific embodiment, an aluminum alloy suitable for HPDC and capable of age-hardening consists essentially of: about 0 to about 0.5 weight percent copper (Cu); and about 0 to about 1 weight percent nickel (Ni).
According to a very specific embodiment, an aluminum alloy suitable for HPDC and capable of age-hardening consists essentially of: at least about 78 to about 90 weight percent aluminum (Al); about 7 to about 15 weight percent silicon (Si); about 0 to about 0.6 weight percent magnesium(Mg); about 0 to about 1 weight percent iron (Fe); about 0 to about 1 weight percent manganese (Mn); about 0 to about 1.0 weight percent zinc (Zn); about 0 to about 0.1 weight percent strontium (Sr); about 0 to about 0.5 weight percent titanium (Ti); about 0 to about 0.5 weight percent zirconium (Zr); about 0 to about 0.5 weight percent vanadium (V); about 0 to about 0.5 weight percent copper (Cu); and about 0 to about 1 weight percent nickel (Ni).
The table of FIG. 3 sets forth a comparison of the calculated quantity ranges of second phase chemicals between an illustrative embodiments according to the invention and several conventional HPDC alloys, including A380, 383, and 360, as well as two proprietary alloys, P011783 and P020385. As can be seen from the table, the array of particles is unique to this invention, and maintains relatively low amounts of most particles, including Cu. Other particles, including Mn and Ni, are utilized in larger quantities than in the other depicted alloys. Likewise, while Sn is used in most of the other alloys, it is not found in the present invention. Additionally, Ti, Sr, and Zr are not used in the A380, 383, or 360 alloys, but are represented by the present invention. Finally, the particle vanadium (V), is not found in any of the alloys except the new composition. The embodiments of the present invention are capable of use for high temperature and corrosive applications, as well as having improved mechanical properties. The new alloy offers the best combination of good castability, high mechanical properties particularly at elevated temperatures, and corrosion resistance. Also, the new alloy reduces the alloy density, material, and manufacturing cost whole improving integrity of HPDC aluminum castings and performance. The new alloy is also expected to reduce aluminum casting product development cycles and time to market.
Referring to the certain specific embodiments, the use of some elements in the present application is uncommon for aluminum alloys. Strontium has been used in aluminum alloys to improve ductility and die soldering resistance. Strontium is known to modify the aluminum-silicon eutectic, which can be achieved at very low levels. However, it is desirable to avoid using higher addition levels, as they are associated with casting porosity. Likewise, titanium is an element that may be added to an aluminum alloy as a grain refiner, as well as improving the strength-to-weight ratio and corrosion resistance. Titanium can also be included at concentrations greater than those required for grain refinement to reduce cracking tendencies and to improve high temperature performance. Zirconium is used in alloys largely for its corrosion resistance and high temperature performance. Forming a fine intermetallic precipitate that inhibits recovery and recrystalization is another effect of zirconium addition to the alloy. Finally, vanadium is generally known for resisting corrosion, and can be used as a stabilizer in an aluminum alloy. It has also been found to significantly improve other properties, such as strength in jet engines and airframes.
A key benefit afforded by the inventive alloys is that the corrosion problems known in the art as associated with Cu content may be eliminated or greatly reduced without compromising the strength of the HPDC cast article. The use of no-, or low-Cu in the alloy largely resolved this issue. FIG. 4 and FIG. 5 further illustrate this point. FIG. 4 is a tabled collation of data generated in an experiment testing and comparing HPDC cast samples, T5 samples, and T5 and soaked samples, from known HPDC A380 and A360 alloys and specific alloy embodiment #1 according to the invention. For the T5 data, the casts were subject to T5 aging. Compositions, tensile properties of the castings, and corrosion conductivity data are all displayed for comparison purposes. FIG. 5 is a tabled collation of data generated in an experiment testing and comparing HPDC cast samples, T5 samples, and T5 and soaked samples, from known HPDC A380 and A360 alloys and specific alloy embodiment #2 according to the invention. Inspection of the data reveals that both embodiment #1 and #2, which do not contain Cu, possess much better corrosion resistance compared with the existing HPDC alloys exemplified by A380 and A360. Experiencing corrosion of less than about 0.1 millimeters per year, or between about 0.09 and 0.07 millimeters per year, is expected for certain embodiments of this invention. Further, embodiments #1 and #2 have better as-cast tensile properties, and better aging response and thus higher tensile strengths after T5 heat treatment in comparison with exemplary HPDC alloys A380 and A360. Additionally, the T5 samples after being further soaked at 200° C. for 200 hours and tested at 200° C., the properties of the present formulations are improved over the A380 and A360 alloys, as is depicted. For each of all of the samples have yield strength above about 150 MPa, ultimate tensile strength above about 190 MPa, and strain above about 1.8 percent. Notably the alloy according to the invention is also slightly lighter providing an additional cost efficiency benefit.
According to another embodiment, an HPDC article cast from a substantially Cu-free aluminum alloy formulated according to the disclosure is provided. Unlike conventionalCu-containing alloys, the Cu-free or low-Cu alloy may undergo a very short (i.e. 10 minutes) T4 solution treatment without causing blister problem, to produce effective temper or T6/T7 age-hardening treatments. In comparison with Cu, Mg has high diffusivity in Al—Si alloy and thus requires much shorter solution treatment time. Due to the absence of Cu in the present invention, or significantly lower levels of Cu, only the Mg and Si participles need to dissolve during solution treatment. Therefore the present invention, having relatively higher concentrations of Mg and Si and relatively lower concentrations of Cu, is capable of a shortened solution treatment. In specific embodiments, the cast article may be solution-treated at treatment temperatures of around 500° C. According to the present invention, Mg₂Si particle dissolution during solution treatment can be completed with 25 minutes at 450° C. even for the largest particle size of 10 um. Generally, for HPDC parts, the typical Mg₂Si particle size is less than 5 um, even in thick section, such as the bulk head area of an engine block. In one embodiment of the present invention, solution treatment of the die cast parts with the disclosed alloys can be solution-treated in as short as 5 minutes. The cast article may exhibit a microstructure comprising at least one or more of the insoluble solidified and/or precipitated particles with at least one alloying element selected from the group consisting of Al, Si, Mg, Fe, Mn, Zn, Sr, Ti, Zr, V, Cu, Ni.
According to other embodiments, an HPDC manufacturing process is provided wherein a molten substantially Cu-free or low-Cu aluminum alloy is provided and cast into a die under high pressure. The alloy solidifies in the die to form the casting, and the casting in the die is permitted to cool to a desired quenching temperature, which is generally empirically determined. The casting may be removed from the die and quenched in a quenching solution. The casting may be subject to one or more steps of age-hardening temper treatments. The casting may also be subjected to solution heat treatment for a time from about 5 minutes to about 25 minutes. This treatment may be performed after quenching the casting and before subjecting the casting to at least one age-hardening treatment. Alternatively, this short solution treatment may be performed immediately after the casting is made and ejected from the die while the casting is still heated to save energy and reduce cost when reheating.
According to very specific embodiments, the method of manufacturing a high pressure die casting of an aluminum alloy comprises: providing a molten aluminum alloy consisting essentially of at least about 78 to about 90 weight percent aluminum (Al), about 7 to about 15 weight percent silicon (Si), about 0 to about 0.6 weight percent magnesium (Mg), about 0 to about 1 weight percent iron (Fe); about 0 to about 1 weight percent manganese (Mn), about 0 to about 1.0 weight percent zinc (Zn), about 0 to about 0.1 weight percent strontium (Sr), about 0 to about 0.5 weight percent titanium (Ti), about 0 to about 0.5 weight percent zirconium (Zr), about 0 to about 0.5 weight percent vanadium (V), about 0 to about 0.5 weight percent copper (Cu), and about 0 to about 1 weight percent nickel (Ni); casting the molten aluminum alloy into a die under high pressure; solidifying the alloy 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 age-hardening treatment.
It is noted that terms like “generally,” “commonly,” and “typically,” when utilized herein, are not utilized to limit the scope 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 particular aspects of an embodiment or to emphasize alternative or additional features that may or may not be utilized in a particular embodiment.
For the purposes of describing and defining embodiments herein it is noted that the terms “substantially,” “significantly,” and “approximately” are utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms “substantially,” “significantly,” and “approximately” are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
Having described embodiments of the present invention in detail, and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the embodiments defined in the appended claims. More specifically, although some aspects of embodiments of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the embodiments of the present invention are not necessarily limited to these preferred aspects.

Claims

What is claimed:

1. An aluminum alloy suitable for high pressure die casting and capable of temperature-elevated age-hardening, the alloy comprising:

at least about 78 weight percent aluminum (Al);

about 7 to about 15 weight percent silicon (Si);

about 0 to about 0.6 weight percent magnesium (Mg);

about 0 to about 1 weight percent iron (Fe);

about 0 to about 1 weight percent manganese (Mn);

about 0 to about 1.0 weight percent zinc (Zn);

about 0 to about 0.1 weight percent strontium (Sr);

about 0 to about 0.5 weight percent titanium (Ti); and

about 0 to about 0.5 weight percent zirconium (Zr).

2. The alloy according to claim 1, further comprising:

about 0 to about 0.5 weight percent vanadium (V).

3. The aluminum alloy according to claim 1, the alloy comprising;

about 13 weight percent silicon (Si);

about 0.4 weight percent magnesium (Mg);

about 0.4 weight percent iron (Fe);

about 0.8 weight percent manganese (Mn);

about 0.5 weight percent zinc (Zn);

about 0.04 weight percent strontium (Sr);

about 0.3 weight percent titanium (Ti);

about 0.15 weight percent zirconium (Zr); and

a balance of aluminum (Al).

4. The aluminum alloy according to claim 2, the alloy comprising;

about 8.5 weight percent silicon (Si);

about 0.4 weight percent magnesium (Mg);

about 0.4 weight percent iron (Fe);

about 0.5 weight percent manganese (Mn);

about 0.5 weight percent zinc (Zn);

about 0.04 weight percent strontium (Sr);

about 0.3 weight percent titanium (Ti);

about 0.3 weight percent zirconium (Zr);

about 0.3 weight percent vanadium (V); and

a balance of aluminum (Al).

5. The alloy according to claim 1, further comprising:

about 0 to about 0.5 weight percent copper (Cu); and

about 0 to about 1 weight percent nickel (Ni).

6. A high pressure die cast article, cast from an aluminum alloy according to claim 1.

7. The cast article according to claim 6 having undergone age-hardening at elevated temperature.

8. The cast article according to claim 6, wherein the cast article undergoes a solution heat treatment for a time from about 5 minutes to about 25 minutes.

9. The cast article according to claim 7, exhibiting corrosion of less than about 0.1 mm/year.

10. The cast article according to claim 7, wherein age-hardening conditions comprise an effective temper, T6, or T7 treatments.

11. The cast article according to claim 7, wherein the cast article being as-cast, age-hardened by a temper T5 treatment, or age-hardened by a temper T5 treatment and then soaked at 200° C. for 200 hours and tested at 200° C. exhibits a yield strength above about 150 MPa, ultimate tensile strength above about 190 MPa, and strain above about 1.8 percent.

12. The cast article according to claim 10, wherein the cast article is solution-treated at a temperature around 500° C.

13. An aluminum alloy suitable for high pressure die casting and capable of age-hardening, the alloy consisting essentially of:

at least about 78 to about 90 weight percent aluminum (Al);

about 7 to about 15 weight percent silicon (Si);

about 0 to about 0.6 weight percent magnesium(Mg);

about 0 to about 1 weight percent iron (Fe);

about 0 to about 1 weight percent manganese (Mn);

about 0 to about 1.0 weight percent zinc (Zn);

about 0 to about 0.1 weight percent strontium (Sr);

about 0 to about 0.5 weight percent titanium (Ti);

about 0 to about 0.5 weight percent zirconium (Zr);

about 0 to about 0.5 weight percent vanadium (V);

about 0 to about 0.5 weight percent copper (Cu); and

about 0 to about 1 weight percent nickel (Ni).

14. A high pressure die cast article, cast from an aluminum alloy according to claim 13.

15. The cast article according to claim 14 exhibiting a casting 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, Sr, Ti, Zr, V, Cu, Ni.

16. A method of manufacturing a high pressure die casting of an aluminum alloy, the method comprising:

providing a molten aluminum alloy comprising:

at least about 78 weight percent aluminum (Al);

about 7 to about 15 weight percent silicon (Si);

about 0 to about 0.6 weight percent magnesium (Mg);

about 0 to about 1 weight percent iron (Fe);

about 0 to about 1 weight percent manganese (Mn);

about 0 to about 1.0 weight percent zinc (Zn);

about 0 to about 0.1 weight percent strontium (Sr);

about 0 to about 0.5 weight percent titanium (Ti); and

about 0 to about 0.5 weight percent zirconium (Zr);

casting the molten aluminum alloy into a die under high pressure;

solidifying the alloy in the die to form the casting;

cooling the casting in the die to a quenching temperature;

quenching the casting in a quenching solution; and

subjecting the casting to at least one age-hardening treatment.

17. The method according to claim 16, wherein the casting exhibits corrosion of less than about 0.1 mm/year.

18. The method according to claim 16, wherein the casting being as-cast, age-hardened by a temper T5 treatment, or age-hardened by a temper T5 treatment and then soaked at 200° C. for 200 hours and tested at 200° C. exhibits a yield strength above about 150 MPa, ultimate tensile strength above about 190 MPa, and strain above about 1.8 percent.

19. The method according to claim 16, wherein the casting is subject to solution heat treatment for a time from about 5 minutes to about 25 minutes.

20. A method of manufacturing a high pressure die casting of an aluminum alloy, the method comprising:

providing a molten aluminum alloy consisting essentially of at least about 78 to about 90 weight percent aluminum (Al), about 7 to about 15 weight percent silicon (Si), about 0 to about 0.6 weight percent magnesium (Mg), about 0 to about 1 weight percent iron (Fe); about 0 to about 1 weight percent manganese (Mn), about 0 to about 1.0 weight percent zinc (Zn), about 0 to about 0.1 weight percent strontium (Sr), about 0 to about 0.5 weight percent titanium (Ti), about 0 to about 0.5 weight percent zirconium (Zr), about 0 to about 0.5 weight percent vanadium (V), about 0 to about 0.5 weight percent copper (Cu), and about 0 to about 1 weight percent nickel (Ni);

casting the molten aluminum alloy into a die under high pressure;

solidifying the alloy 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 age-hardening treatment, wherein the casting exhibits corrosion of less than about 0.1 mm/year and exhibits a yield strength above about 150 MPa, ultimate tensile strength above about 190 MPa, and strain above about 1.8 percent after the casting is soaked at 200° C. for 200 hours and tested at 200° C.