GB2568310A - Aluminium alloy for high presure die casting - Google Patents

Abstract

An aluminium alloy which comprises (by weight): 3.0-12.0 % magnesium, 0.5-5.0 % iron, at most 1.5 % rare earth element(s) (including Sc and/or Y), at most 2.5 % manganese, at most 100 ppm beryllium, at most 0.3 wt.% Si and other alloying elements and impurities 0-0.4% each and less than 0.5 % in total, with the balance being aluminium. The alloy can be used to make high pressure die cast components which in the as-cast condition have a 0.2 % proof stress of more than 150 MPa, a UTS of more than 290 MPa and an elongation of at least 6 %. The alloy can be used to make engine components, vehicle wheels, steering wheels and columns, a vehicle frame and chassis members, a gear box and powertrain components.

Description

ALUMINIUM ALLOY FOR HIGH PRESSURE DIE CASTING

TECHNICAL FIELD

The present disclosure relates to an alloy and particularly, but not exclusively, to aluminium casting alloys for use in castings of structural components. Aspects of the invention relate to an alloy composition, the use of such an alloy composition, a cast product comprising an alloy composition, a vehicle comprising a cast product, and to a process for manufacturing a cast product.

BACKGROUND

Die-casting is a well-developed technical process by means of which parts may be manufactured from alloys, especially aluminium alloys. Aluminium die cast parts are especially useful where high stress and high ductility are critical and have particular application in the automotive and aerospace industries where aluminium die castings have been substituted for steel components to reduce weight whilst retaining the necessary strength and corrosion resistance.

High pressure die casting (HPDC) in particular has been extensively used to cast aluminium alloys. In comparison with other casting methods, the HPDC process offers a number of advantages in terms of allowing high volume, economic production, with the resulting cast products having a fine grain microstructure to achieve good mechanical properties, as well as allowing dimensional accuracy suitable for production of intricate shapes and thin wall castings with a good surface finish.

The properties of a die cast part may be influenced by several factors, including the quality and adjustment of the die casting machinery, the chemical composition of the alloy and the process by which the liquid alloy composition is prepared and then cast. The alloy composition itself is one of the most critical factors and has a significant influence on castability, the feeding behaviour and the life of the casting tools, as well as on the mechanical characteristics of the cast product.

To meet the stringent requirements of strength, ductility and resistance to metal fatigue whilst retaining good castability, aluminium-silicon eutectic system alloys (silumin) have been favoured for the purposes of die castings. Conventionally, aluminium-silicon alloys used in motor vehicle castings consist of a major component of aluminium, between 8 and 10 wt% silicon as well as minor amounts (between 0.1 wt% and 1 wt%) of additional grain refining and strengthening additive elements such as copper, zinc, manganese, magnesium, strontium and titanium.

A significant problem with aluminium-silicon alloys for use in die castings is controlling the iron content. Iron represents an impurity due to the fact that it forms inter-metallics within the microstructure of the alloy that can lead to weakening, increased vulnerability to fatigue and reduced ductility. In die-cast aluminium alloys, iron is commonly present as an impurity element as it is unavoidably picked up in practice, for example through use of steel tools during melting and casting, and when scrapped and recycled materials are used. The detrimental effect of iron may be due to its low equilibrium solubility in the α-AI solid phase (<0.04 wt.%) and the associated strong tendency to form various low symmetry Al-Fe or Al-Fe-Si intermetallic phases. When these low symmetry compounds crystallise as primary phases during solidification, they are prone to grow into long needles/plates. Such Fe-rich intermetallic phases are generally brittle and act as stress raisers which weaken the coherence of the alloy, thereby reducing the mechanical strength of the resulting cast alloys and introducing vulnerability to fatigue and reduced ductility.

Generally, the effect of Fe-rich intermetallic phases in aluminium alloys on the mechanical properties depends on their type, size and amount in the microstructure. In order to diminish the detrimental effect of iron, several metallurgical solutions are effectively used, which include (1) avoiding or reducing the formation of low symmetry Al-Fe or Al-Fe-Si compounds by making the Fe levels as low as economically possible; (2) modifying the crystal structures from low symmetry compounds to high symmetry lattice types in the castings; (3) refining the intermetallic phases by physical methods, including use of a superheated melt, solidifying under a rapid cooling rate, and/or adopting a melt treatment, or by chemical approaches such as adding Ca or Sr elements prior to solidification; and (4) using non-equilibrium heat treatment of the castings to spheroidise the needle or plate-shaped Fe-rich intermetallic phases.

Examples of alloy compositions for cast aluminium products are known from the prior art.

WO 2006/122341 describes an aluminium alloy with the composition of 4.5 to 6.5% by weight magnesium (Mg), 1.0 to 3.0% by weight silicon (Si), 0.3 to 1.0% by weight manganese (Mn), 0.02 to 0.3% by weight chromium (Cr), 0.02 to 0.2% by weight titanium (Ti), 0.02 to 0.2% by weight zirconium (Zr), one of rare earth elements from 0.005 to 1.6% by weight, and iron (Fe) max. 0.2% by weight.

WO 2005/047554 describes an aluminium alloy with the composition of at least 1.0 to 8.0 wt.% magnesium (Mg), > 1.0 to 4.0 wt.% silicon (Si), 0.01 to < 0.5 wt.% scandium (Sc), 0.005 to 0.2 wt.% titanium (Ti), 0.5 wt.% of an element or group of elements, selected from the group comprising zirconium (Zr), hafnium (Hf), molybdenum (Mo), terbium (Tb), niobium (Nb), gadolinium (Gd), erbium (Er) and vanadium (V), 0-0.88 wt.% manganese (Mn), 0-0.3 wt.% chromium (Cr), 0-1.0 wt.% copper (Cu), 0-0.1 wt.% zinc (Zn), 0 -0.6 wt.% (preferably 0.05-0.2 wt.%) iron (Fe), 0-0.004 wt.% beryllium (Be) and the remainder aluminium with further impurities to an individual max. of 0.1 wt.% and total max. of 0.5 wt.%.

US 2005/0173032 describes a casting alloy with a composition of 2 to 4 w. % magnesium, 0.9 to 1.5 wt.% silicon, 0.1 to 0.4 wt.% manganese, 0.1 to 0.4 wt.% chromium, max. 0.2 wt.% iron, max. 0.1 wt.% copper, max. 0.2 wt.% zinc, max. 0.2 wt.% titanium, max. 0.3 wt.% zirconium, max. 0.008 wt.% beryllium, max. 0.5 wt.% vanadium, with aluminium as the remainder, with further elements and productioninduced contaminants individually max. 0.02 wt.%, total max. 0.2 wt.%.

AT 407 533 describes an aluminium alloy composition of >3.0 to 7.0% by weight magnesium, 1.0 to 3.0% by weight silicon, 0.3 to 0.49% by weight manganese, 0.1 to 0.3% by weight chromium, 0 to 0.15% by weight titanium, max. 0.15% by weight iron, max. 0.00005% by weight each of calcium and sodium, and max. 0.0002% by weight phosphorus.

EP-B-0 792 380 describes an alloy composition of 3.0 to 6.0, preferably 4.6 to 5.8% by weight magnesium, 1.4 to 3.5, preferably 2.0 to 2.8% by weight silicon, 0.5 to 2.0, preferably 0.6 to 1.5% by weight manganese, max. 0.2, preferably 0.1 to 0.2% by weight titanium and max. 0.15, preferably max. 0.1% by weight iron and the rest being aluminium and residual impurities.

WO 1996/025528 describes an Al-Mg based alloy with 2.5 - 4.0% by weight magnesium, max. 0.4% by weight manganese, max. 0.6% by weight iron, max. 0.45% by weight silicon, max. 0.10% by weight copper, < 0.003% by weight beryllium with the remainder being aluminium.

WO 1996/030554 describes an aluminium alloy for casting operations with 2 to 5 wt.% magnesium, up to 0.3 wt.% silicon, 0.2 to 1.6 wt.% manganese, up to 1 wt.% iron, and between about 0.1 to 0.3 wt.% zirconium, with the balance substantially aluminium and incidental elements and impurities.

In order to avoid reduction of elongation to a level that cannot fulfil the requirement of structural parts, it is commonly preferred that the iron content in these aluminium alloys is maintained at a level that is below 0.2wt%, and preferably even lower. Often manganese is required in association with Al-Mg alloys for neutralising iron compounds. Despite the adverse effects on the mechanical properties of cast aluminium alloys resulting from the presence of iron, its inclusion can be beneficial to prevent or at least reduce die soldering in an HPDC process. Thus there is an inherent tension between the composition and processing demands.

In addition, it is desirable to increase the amount of recycled material used within aluminium alloys, which inherently leads to a need for increased levels of iron to be tolerated.

There is a need therefore to provide a die cast Al-Mg alloy that is capable of providing an excellent balance of strength and ductility under as-cast condition in comparison with those of standard Al-Mg-Si and Al-Mg type alloys, such as UK LM5.

Accordingly, it is an aim of the present invention to provide alloy compositions for use in an HPDC process having a balance of strength and ductility under as-cast condition. These and other uses, features and advantages of the invention should be apparent to those skilled in the art from the teachings provided herein.

SUMMARY OF THE INVENTION

Against this background, the invention resides in a first aspect in an aluminium alloy for high pressure die casting comprising:

3.0 wt.% to 12.0 wt.% magnesium;

0.5 wt.% to 5.0 wt.% iron;

0.2 wt.% to 2.5 wt.% manganese; and at most 0.3 wt.% silicon.

Whilst not being bound by theory, it is believed that the enhanced iron content in the Al-Mg alloy of the invention enables formation of sufficient Fe-rich intermetallic compounds to improve the strength of the alloy under as-cast condition. At the same time, high ductility of the Al-Mg alloy can be maintained to a level that is sufficient for general industrial application.

The inclusion of minor alloying elements, each in an amount of 0.4 wt.% or less, and less than 0.5 wt.% in total, may assist in neutralising Fe by forming different compounds. The ability to increase Fe content by means of the invention opens up the opportunity for producing alloys using cheaper recycled materials without sacrificing the various properties required for structural components.

An example of an alloy according to one embodiment of the invention has the following composition: 3.0 wt.% to 12.0 wt.% magnesium; 0.5 wt.% to 5.0 wt.% iron; from 0.2 wt.% to 2.5 wt.% manganese; optionally from 5ppm to 100ppm beryllium; optionally from 0.01 wt.% to 1.5 wt.% rare earth element(s); other minor alloying elements and impurities, each in an amount of 0.4 wt.% or less, and less than 0.5 wt.% in total; and, as balance, aluminium.

According to a further embodiment, the aluminium alloy composition as described above may be used in the manufacture of a high pressure die cast product.

According to another aspect of the invention presented herein, there is provided a cast product comprising the aluminium alloy as described.

According to another aspect, there is provided a cast product comprising the aforementioned aluminium alloy, wherein the cast product may be a vehicle component, optionally selected from one or more of the group consisting of: an engine component; a vehicle wheel; a steering wheel; a steering column; a frame member; a gear box; a powertrain component; a chassis component; a body component and a transmission system.

According to a further aspect, there is provided a vehicle comprising the cast product as described above.

According to a further embodiment the vehicle may be selected from the group consisting of: an automobile; a motorcycle; a locomotive; a watercraft and an aircraft.

According to a further aspect, there is provided a process for manufacturing a cast product, the process comprising casting an aluminium alloy as described above into a mould or die that defines the cast product.

According to a further aspect, there is provided a process for manufacturing a cast product, the process comprising casting an aluminium alloy as described above into a mould or die that defines the cast product.

According to a further embodiment, there is provided the process as described above, wherein the cast product may be manufactured by die casting.

According to a further embodiment, there is provided the process as described above, wherein the cast product is manufactured by high-pressure die casting.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a flow chart showing the cast product manufacturing process.

Figure 2 is a drawing of a vehicle comprising a cast product.

DETAILED DESCRIPTION

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

A number of definitions are provided below that will assist in the understanding of the invention.

As used herein, the term comprising or “containing” means any of the recited elements are necessarily included, and where indicated other elements may optionally be included as well. Consisting essentially of” means any recited elements are necessarily included, elements that would materially affect the basic and novel characteristics of the listed elements are excluded, and other elements may optionally be included. Consisting of” means that all elements other than those listed are excluded. Embodiments defined by each of these terms are within the scope of this invention.

The term “alloy” is used herein to denote a metallic composition comprising a mixture of a predominating metallic element and other elements, including impurities. A basic aluminium-magnesium (Al-Mg) alloy may contain 0.5 to 13 wt.% Mg, in which the lowmagnesium alloys have the better formability, and the high-magnesium alloys have acceptable castability and strength. In order to improve strength and prevent or reduce grain growth upon recrystallization, commercial Al-Mg alloys contain small additions of manganese, chromium and titanium are usually used in the cast Al-Mg alloys.

“Casting” is a manufacturing process that can produce metal components through the use of moulds. In an HPDC process the mould may take the form of a reusable die. The casting process involves a furnace, metal and the mould. Alternatively, a casting machine may also be used to apply pressure to the mould or die during the casting process. The alloy comprising aluminium is first melted in the furnace and then poured or injected, under pressure, into the mould. Once the casting has cooled and has set the part can be subjected to additional tooling or trimmed and finished. The cutting of the cast metal product is also known as machining. Casting processes can produce large and small component parts, with geometrically complex shapes. The cast parts are typically of high strength and can be subjected to considerable loads when in use.

As mentioned, components manufactured via die casting processes of the present invention are also referred to as ‘parts’ and broadly refer to any metal object manufactured via the casting process. The parts are often comprised of geometrically complex shapes that perform a defined function. Components manufactured according to the present invention are particularly suitable for use in motor vehicles, locomotives, static engines, watercraft (marine) and aircraft.

As used herein, the term “balance”, when used in reference to a particular element, is used to describe that the remainder of the composition (in wt.%), excluding any alloying additions, is comprised of the designated element. Hence, the total composition including the “balance” element in combination with other stated alloying elements is equal to 100 wt.% of the alloy composition. The term “impurity” refers to a metallic or non-metallic element that is present in an alloy but which is not added intentionally. In embodiments of the present invention where only specific component elements are specified, the balance of the alloy may comprise aluminium.

As used herein, the phrase “rare earth metal”, is used to describe one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium. Promethium may be excluded, in certain embodiments, due to its radioactive properties.

The term “mould”, as used herein, is referring to a hollow container used to give shape to molten or hot liquid material when it cools and hardens.

The term “die”, as used herein, is referring to a block with a special shape or with a pattern cut into it that is used for shaping pieces of metal.

The phrase “cast product” is used herein to denote an entity that has been cast in metal from a die or a mould.

The term “as-cast” is used herein to refer to a casting in the condition in which it comes out of the foundry, before any work-hardening or additional heat treatment is carried out.

As used herein, the term “vehicle” is used to denote any means in or by which people, animals or goods are transported or conveyed. Typically, vehicles may include road transport motor vehicles as well as rail locomotives. Watercraft may include marine vessels, such as boats, ships, submarines and hovercraft. Aircraft may include fixed wing or non-fixed wing aircraft, as well as spacecraft.

As mentioned the casting processes can produce large and small cast products also referred to as component parts. The term “vehicle component” is referring to any part that is deployed in a vehicle.

Turning now to a specific embodiment of the invention, the casting alloy may have the following composition:

3.0 wt.% to 12.0 wt.% magnesium;

0.5 wt.% to 5.0 wt.% iron;

at most 1.5 wt.% rare earth element(s);

at most 2.5 wt.% manganese;

at most 100ppm beryllium; and other minor alloying elements and impurities, each in an amount of at most 0.4 wt.%, and at most 0.5 wt.% in total;

with the balance being aluminium.

In a further specific embodiment of the invention, the casting alloy may have the following composition:

3.0 wt.% to 12.0 wt.% magnesium;

0.5 wt.% to 5.0 wt.% iron;

optionally from 0.01 wt.% to 1.5 wt.% rare earth element(s);

optionally from 0.2 wt.% to 2.5 wt.% manganese;

optionally from 5ppm to 100ppm beryllium; and other minor alloying elements and impurities, each in an amount of 0.4 wt.% or less, and less than 0.5 wt.% in total;

with the balance being aluminium.

According to another specific embodiment of the invention, a casting alloy may have the following composition:

magnesium 4.0 to 12% by weight, iron from 0.5 to 5.0% by weight, optionally manganese 0.2 to 2.5% by weight, optionally rare earth element 0.01 to 1.5 % by weight, optionally beryllium from 5ppm to 100ppm, and impurity and minor alloying elements at most 0.4 wt.% each and less than 0.5 wt.% in total of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), calcium (Ca), antimony (Sb), bismuth (Bi), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), silicon (Si) and boron (B), and the balance aluminium.

According to other embodiments, the Fe content may be less than 4 wt.%, or less than

3.5 wt.%. In another embodiment, the Fe content may be more than 1.5 wt.%.

According to further embodiments, the Mg content of the alloy may be more than 4 wt.%, or more than 4.5 wt.%. In other embodiments, the Mg content may be less than

8.5 wt.%, or less than 6.5 wt.%.

Mn may be beneficial for combining with Fe to alter the morphology of Fe-containing compounds from needle-like morphology to a nodular morphology. Additionally, the presence of Mn may serve to reduce the tendency of a die to stick to die cast parts.

The amount of Mn is determined to provide a desired balance of process control and a combination of strength and ductility.

Thus, according to a further embodiment, the manganese (Mn) content of the alloy may be more than 0.2 wt.% and less than 2.5 wt.%, or less than 1.5 wt.%, or less than 1.2 wt.%. In other embodiments, the Mn content may be more than 0.4 wt.%.

Rare earth (RE) metals may be used in the alloy composition and may be selected from one or more of the group consisting of: lanthanum (La); cerium (Ce); neodymium (Nd); yttrium (Y); ytterbium (Yb); erbium (Er) and gadolinium (Gd). Mixtures of lanthanides may be used, typically referred to as mischmetal. The rare earth elements, in particular La and Ce, may be added to the alloy for better ductility of the cast product. Mixtures of Ce and La are economically advantageous. In one embodiment, a master alloy of Ce and La may be used in the composition of the present invention. In another embodiment, a mischmetal containing mainly Ce with some La, with minor amounts of Pr and Nd may be utilised. For example, mischmetal consisting essentially of Ce (48-54 wt.%), La (24-30 wt.%), Pr (4-7 wt.%) and Nd (14-18 wt.%) may be used.

According to a further embodiment, the amount of rare earth metal in the alloy of the invention may be 0.01 wt.% or more and up to 1.5 wt.%, or less than 0.8 wt.%, or less than 0.4 wt.%.

The inclusion of beryllium (Be) in the alloy composition is beneficial for inhibiting oxidation. When included, Be may be used in amounts of from 5ppm to 100ppm. In other embodiments, the Be content of the alloy may be less than 60ppm, or less than 30ppm, or greater than 10ppm.

Any minor alloying elements in the composition of the invention may be selected from titanium (Ti), zirconium (Zr), niobium (Nb), calcium (Ca), antimony (Sb), bismuth (Bi), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), silicon (Si) and boron (B).

According to an embodiment, any minor alloying elements and impurities, are present each in an amount of 0.4 wt.% or less. According to a further embodiment, minor alloying elements, especially but not limited to silicon, and impurities may be present in an amount of 0.3 wt.% or less.

In embodiments of the invention, Ti can refine primary aluminium grains and therefore increase both the strength and elongation of the alloys. Thus, according to an embodiment, Ti may be present as a minor alloying element for improving grain refining during solidification of the alloy casting. Ti may be present at a concentration of less than 0.4 wt.%, or less than .0.3 wt.%, or less than 0.25 wt.%. In another embodiment, Ti may be present at a concentration of at least 0.01 wt.%.

In other embodiments, Ti may be replaced in part or in whole by zirconium (Zr) and/or scandium (Sc), and/or niobium (Nb), and/or boron (B), and/or gadolinium (Gd), and/or yttrium (Y) and/or vanadium (V), and/or chromium (Cr) with the amounts being in the same compositional range as that of Ti described above.

The alloy may contain zinc as inevitable impurity - for example if the alloy contains recycled material - with at least about 0.001 wt.%, or about 0.05 wt.%, or about 0.10 wt.%, or about 0.15 wt.%; and with at most about 0.2 wt.%, or about 0.3 wt.%, or about 0.4 wt.%. It is desirable to incorporate a high level of tolerance to zinc in the aluminium alloy whilst maintaining the mechanical properties as this allows the cost effective use of recycled materials.

In another specific embodiment, the casting alloy has the following composition:

4.0 to 8.5% by weight magnesium;

0.5 to 4.0% by weight iron;

0.2 to 1.5% by weight manganese;

0.01 to 0.8 by weight rare earth element(s);

5ppm to 60ppm beryllium; and impurity and minor alloying elements at most 0.25 wt.% each and less than 0.5 wt.% in total of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), calcium (Ca), antimony (Sb), bismuth (Bi), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), silicon (Si) and boron (B), with the remainder being aluminium.

In a yet further specific embodiment, the casting alloy has the following composition:

4.5 to 6.5% by weight magnesium;

1.5 to 3.5% by weight iron;

0.4 to 1.2% by weight manganese;

0.01 to 0.4 by weight rare earth element(s),

10ppm to 30ppm beryllium, and impurity and minor alloying elements at most 0.2 wt.% each and less than 0.4 wt.% in total of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), calcium (Ca), antimony (Sb), bismuth (Bi), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), silicon (Si) and boron (B), with the remainder being aluminium.

An example of a method of producing the casting alloy will now be described. The manufacturing process may comprise the steps of:

a) heating Al, Fe, Mn (in the form of substantially pure metal ingots or master alloy ingots) to a temperature of at least 750 °C to form a melt;

b) adding to the melt a Be-containing alloy, optionally in master alloy ingot form, that has been preheated to a temperature of least 200°C;

c) adding to the melt Mg, optionally in ingot form, that has been preheated to a temperature of at least 200°C;

d) agitating the melt to provide a homogenized mixture;

e) adding to the homogenized melt rare earth-containing alloy(s) and minor alloying elements, optionally in master alloy ingot form, that have been preheated to a temperature of at least 200°C;

f) maintaining the melt at a temperature of at least 50 °C above its liquidus and optionally removing periodically slugs that may form on the melt;

g) degassing the melt of H₂, optionally by means of N₂, Ar or other suitable gas, to a pre-determined level of H₂ in the melt;

h) determining the chemical composition of the melt in the crucible and, if necessary, adjusting the chemical composition by adding required elements into the melt to achieve a required amount of each element.

According to further embodiments, the aforementioned process may further include one or more of the following steps: after step a) and before step b), removing any slugs on the surface of the melt and/or adding flux to the surface of the melt; in step c) introducing Mg below any flux added prior to step b); and during step d) agitating the melt vigorously to assist dissolution of Mg in the melt; after step h) maintaining the melt at a temperature of about 60°C above liquidus to be ready for submitting to a die casting process.

A typical method of producing a cast product and a cast component using the casting alloy of the invention will now be described. The die block which is usually covered in a water-based die releasing lubricant is preheated using the circulation of mineral oil at about 250 “C. The melted alloy composition 30 shown in Figure 1 having the desired composition as described above is usually injected at a temperature of about 650 “C at an injection speed of about 50 m/s. Immediately after the die cast ‘shot’ an intensification pressure of about 320 bar is applied to reduce gas and shrinkage porosity. The melt is cooled down under pressure. After a cooling period of about 48 hours the cast product 20 may be released from the die and worked up for use or subjected to mechanical testing.

The die casting process as described may be a high pressure die-casting process, including conventional high pressure die casting, and vacuum assisted high pressure die casting processes. Vacuum assisted processes may enhance the mechanical properties and weldability characteristics of the resulting alloy.

The as-cast alloys of the present invention, once cast, exhibit a high strength at both ambient temperatures and at high temperatures (for example, temperatures above 150 °C). These beneficial mechanical properties at both high and ambient temperatures make the cast component ideally suited for vehicle applications. In a particular embodiment of the invention the die-cast product in the as-cast condition demonstrates an ultimate tensile strength (UTS) of more than 290 MPa, a 0.2% yield strength of more than 150 MPa, and an elongation of 6% or greater. In another embodiment, the elongation may be from 6% to 24%.

The mechanical parameters, namely yield strength, the ultimate tensile strength and elongation are determined using the American Society for Testing and Materials (ASTM) standard B557. ASTM B557 is a testing standard that covers the tension testing requirements of wrought and cast aluminium- and magnesium-alloy products. Other organisations proving standards for such testing, which are met by the present invention, are the Society of Automotive Engineers (SAE), the Japan Standards Association (JIS), the Deutsche Institut fOr Normung (DIN), the European Committee for Standardisation (EN) and the International Organisation for Standards (ISO).

The vehicle in which the cast component 20 is deployed may be an automobile 10 shown in Figure 2; a motorcycle; a locomotive; a watercraft or an aircraft. The cast component itself may be an engine component; a vehicle wheel; a steering wheel; a steering column; a frame member; a gear box, a powertrain component, a chassis component, a body component and transmission system. It will be appreciated that the aforementioned list of vehicles and the aforementioned list of components are not intended to be exhaustive, and other vehicles and/or components are contemplated.

The invention is further illustrated by the following non-limiting examples.

Example 1

On an industrial scale of Freeh 450-54 cold chamber high pressure die casting machine with a locking pressure of 4500 kN was used to cast a standard cast product. The casting die was preheated using the circulation of mineral oil at a temperature of about 250° C. A specially designed die was used to cast six ASTM standard samples with three 0 6.35mm round samples. During casting, the injection speed was controlled at 3.5 m/s for the piston, which corresponded to the ingate speed at a level of 50 m/s. The intensification pressure was at 320 bar. A water-based die releasing lubricant was used on the die block, which was pre-heated by the circulation of mineral oil at 250°C in all shots. Some samples were prepared by conventional high pressure die casting, and the others were prepared by the vacuum assisted high pressure die casting processes. The Pfeiffer Vacu²-System had two separate vacuum units that were independent from each other. One of the units was directly connected to the shot sleeve, the other one was to the die.

The tensile tests were conducted following ASTM standard B557, using an Instron 5500 Universal Electromechanical Testing System equipped with Bluehill control software and a 50 kN load cell. All tensile tests were performed at an ambient temperature (20°C). The gauge length of the extensor meter was 25mm.

The composition of alloys and the mechanical properties in the as-cast condition are 5 set out in Table 1 and Table 2, respectively. The alloy according to the invention showed no tendency to die-sticking during the die-casting operation.

Table 1 Chemical composition of the alloys.

Alloy	Mg	Fe	Mn	Zn	Ti	Cr	RE	Be	Al
01	4.0	0.5	0.6	0.16	0.10	0.01	0.01	0.002	Bal.
02	4.0	1.5	0.5	0.15	0.14	0.01	0.01	0.002	Bal.
03	4.0	2.5	0.6	0.14	0.15	0.01	0.01	0.002	Bal.
04	4.1	2.5	0.6	0.17	0.12	0.01	0.10	0.002	Bal.
05	4.0	3.2	0.5	0.20	0.14	0.01	0.20	0.002	Bal.
06	4.0	4.0	0.7	0.16	0.13	0.01	0.35	0.002	Bal.
07	5.0	0.5	0.9	0.21	0.16	0.01	0.02	0.002	Bal.
08	5.0	1.5	0.6	0.17	0.14	0.01	0.01	0.002	Bal.
09	5.0	2.5	0.7	0.15	0.13	0.01	0.15	0.002	Bal.
10	5.0	3.5	0.7	0.18	0.14	0.01	0.25	0.002	Bal.
11	5.6	0.5	1.1	0.18	0.14	0.01	0.02	0.002	Bal.
12	5.4	1.5	0.6	0.18	0.16	0.01	0.02	0.002	Bal.
13	5.5	2.5	0.5	0.18	0.18	0.02	0.10	0.002	Bal.
14	5.5	3.5	0.6	0.17	0.15	0.01	0.20	0.002	Bal.
15	6.0	0.5	0.7	0.13	0.12	0.02	0.01	0.002	Bal.
16	6.1	1.5	0.5	0.10	0.18	0.01	0.01	0.002	Bal.
17	6.0	2.5	0.5	0.12	0.18	0.02	0.14	0.002	Bal.
18	6.0	3.5	0.5	0.10	0.20	0.15	0.20	0.002	Bal.
19	6.4	2.0	0.5	0.15	0.19	0.25	0.16	0.002	Bal.
20	6.5	3.0	0.5	0.15	0.19	0.28	0.34	0.002	Bal.

Table 2 Mechanical properties of the high pressure die-casting alloys.

Alloys	Conventional HPDC	Vacuum assisted HPDC
YS(MPa)	UTS(MPa)	El (%)	YS(MPa)	UTS(MPa)	El (%)
01	143	294	19.8	148	309	23.2
02	145	298	16.1	149	310	19.8
03	146	299	11.9	151	311	14.3
04	147	301	13.4	151	312	15.9
05	146	300	10.2	152	309	13.2
06	150	304	7.0	155	316	10.3
07	148	298	18.1	149	314	21.0
08	151	304	14.7	154	318	17.6
09	152	303	11.9	156	316	14.6
10	155	308	9.8	158	320	12.9
11	152	300	17.7	152	312	20.6
12	154	304	14.6	155	314	18.0
13	157	307	10.5	156	321	13.0
14	162	310	7.9	166	322	10.5
15	155	304	15.0	158	315	17.9
16	157	304	11.6	161	314	14.3
17	160	306	7.8	163	319	10.6
18	164	311	5.4	166	325	8.2
19	161	310	6.1	165	323	9.2
20	165	315	4.2	168	329	6.9

From the results in Table 1 and Table 2 it can be seen that excellent properties are achieved without the need for further heat treatments. In particular, the yield strength is improved by increasing the content of Mg. Improvements in yield strength may also be achieved by increasing the Fe and Mn contents. The addition of rare earth elements (RE) may improve the elongation of the alloys under as-cast condition. The vacuum assisted system offers further improvements in elongation and ultimate tensile strength as compared to conventional HDPC.

Example 2

An automotive component was produced using a Freeh 450-54 cold chamber high pressure die casting machine with and without Pfeiffer vacuum System. The locking pressure of machine was 4500KN. The wall thickness was 2.8 mm for the die-casting. The injection parameters were optimised for each type of casting and the castings were made under the corresponding optimised condition. The dies were heated by the circulation of mineral oil at 250 °C. The pouring temperature was at 650°C measured by a K-type thermocouple. All casting samples were left in ambient conditions for at least 48 hours before the mechanical properties were tested. 20 pieces of such castings were selected for making tensile samples. 5 standard square samples with a cross section of 6.35x2.8 mm were machined from each casting at fixed location. The compositions of alloys were: (A) ( wt.%) AI-5.5Mg-3.0Fe-0.6Mn-0.2Zn-0.15Ti-0.01Cr0.002Be-0.10RE and (B) (wt.%) AI-5.5Mg-3.0Fe-0.6Mn-0.2Zn-0.15Ti-0.01Cr-0.002Be0.25RE. The mechanical properties of machined as-cast samples at room temperature are listed in Table 3 and 4.

Table 3 As-cast mechanical properties (room temperature) of the machined samples from the castings prepared by conventional HPDC process.

	Location	Position 1	Position 2	Position 3	Position 4	Position 5
	Elongation (%)	6.59	6.24	6.04	6.32	6.20
Alloy A	UTS (MPa)	302	298	306	301	304
	Yield strength (MPa)	155	156	162	158	160
	Elongation (%)	7.01	6.82	6.64	6.45	6.84
Alloy B	UTS (MPa)	310	315	318	309	316
	Yield strength (MPa)	163	159	171	163	169

From the results in Table 3 it can be seen that the machined samples cut from different locations of as-cast automotive component were satisfactory in terms of mechanical 5 properties. The yield strength was greater than 150MPa, UTS was greater than 290MPa and elongation was greater than 6%.

Table 4 As-cast mechanical properties (room temperature) of the machined samples from the castings prepared by vacuum assisted HPDC process.

	Location	Position 1	Position 2	Position 3	Position 4	Position 5
	Elongation (%)	9.40	9.06	8.89	9.54	9.05
Alloy A	UTS (MPa)	316	311	320	314	316
	Yield strength (MPa)	159	157	166	162	167
	Elongation (%)	9.98	9.62	9.44	9.65	9.19
Alloy B	UTS (MPa)	323	329	333	321	330
	Yield strength (MPa)	165	161	173	166	172

Although particular embodiments of the invention have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the appended claims, which follow. It is contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims.

Claims (20)

1. An aluminium alloy for high pressure die casting comprising:

3.0 wt.% to 12.0 wt.% magnesium;

0.5 wt.% to 5.0 wt.% iron;

0.2 wt.% to 2.5 wt.% manganese; and at most 0.3 wt.% silicon.

2. An alloy according to claim 1, wherein the alloy comprises from 5ppm to 100ppm beryllium.

3. An alloy according to claim 1 or claim 2, wherein the amount of iron is in the range from 1.5 to 3.5 wt.%.

4. An alloy according to any preceding claim, wherein the amount of magnesium is in the range from 4.0 to 8.5 wt.%.

5. An alloy according to any preceding claim, wherein the amount of manganese is in the range from 0.2 to 1.5 wt.%.

6. An alloy according to any preceding claim, wherein the alloy comprises at least one of:

0.01 wt.% to 1.5 wt.% rare earth element(s); and other minor alloying elements and impurities, each in an amount of 0.4 wt.% or less, and less than 0.5 wt.% in total.

7. An alloy according to any preceding claim, wherein the minor alloying elements are selected from titanium, zirconium, niobium, calcium, antimony, bismuth, vanadium, chromium, copper, zinc, silicon and boron.

8. An alloy according to any preceding claim, wherein the alloy comprises from 5 to 60 ppm beryllium.

9. An alloy as claimed in claim 1 comprising:

3.0 wt.% to 12.0 wt.% magnesium;

0.5 wt.% to 5.0 wt.% iron;

from 0.01 wt.% to 1.5 wt.% rare earth element(s);

from 0.2 wt.% to 2.5 wt.% manganese;

from 5ppm to 100ppm beryllium; and other minor alloying elements and impurities, each in an amount of 0.4 wt.% or less, and less than 0.5 wt.% in total; with the balance being aluminium.

10. An alloy according to claim 9, wherein the alloy comprises:

4.0 to 8.5 wt.% magnesium;

0.5 to 4.0 wt.% iron;

0.2 to 1.5 wt.% manganese;

0.01 to 0.8 wt.% rare earth element(s);

5ppm to 60ppm beryllium; and at most 0.25 wt.% each and less than 0.5 wt.% in total of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), calcium (Ca), antimony (Sb), bismuth (Bi), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), silicon (Si) and boron (B), with the balance being aluminium.

11. An alloy according to any claim 10, wherein the alloy comprises:

4.5 to 6.5 wt.% magnesium;

1.5 to 3.5 wt.% iron;

0.4 to 1.2 wt.% manganese;

0.01 to 0.4 wt.% rare earth element(s);

beryllium from 10ppm to 30ppm, and impurity and minor alloying elements at most 0.2 wt.% each and less than 0.4 wt.% in total of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), calcium (Ca), antimony (Sb), bismuth (Bi), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), silicon (Si) and boron (B), with the balance being aluminium.

12. The use of an aluminium alloy as described in any one of claims 1 to 11 for the manufacture of a high pressure die cast product.

13. A cast product comprising the aluminium alloy of any one of claims 1 to 11.

14. The cast product of claim 13, wherein the cast product in the as-cast condition has an ultimate tensile strength (UTS) of more than 290 MPa, a 0.2% yield strength of more than 150 MPa, and an elongation of 6% or greater.

15. The cast product of claims 13 or 14, wherein the cast product is a vehicle component, optionally selected from one or more of the group consisting of: an engine component; a vehicle wheel; a steering wheel; a steering column; a frame member; and a gear box; a powertrain component; a chassis component; a body component and a transmission system.

16. A vehicle comprising the cast product of any one of claims 13, 14 or 15.

17. The vehicle of claim 16 selected from the group consisting of: an automobile; a motorcycle; a locomotive; a watercraft and an aircraft.

18. A process for manufacturing a cast product, comprising casting an aluminium alloy of any one of claims 1 to 11 into a mould or die that defines the cast product.

19. The process of claim 18, wherein the cast product is manufactured by die casting.

20. The process of claim 19, wherein the cast product is manufactured by high pressure die casting.