GB2500825A

GB2500825A - An Al-Mg-Si-Mn alloy and a method of producing such an alloy

Info

Publication number: GB2500825A
Application number: GB201305827A
Authority: GB
Inventors: Doug Watson
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2012-03-30
Filing date: 2013-04-02
Publication date: 2013-10-02
Anticipated expiration: 2033-04-02
Also published as: WO2013144343A1; GB201205655D0; GB201305827D0; GB2500825B; GB2500825A8; GB2500825B8

Abstract

An aluminium alloy which comprises (by weight): 3.0-8.0 % magnesium, 0.7-4.0 % silicon, 0.1-1.5 % manganese and 0-0.3 % titanium. The alloy preferably comprises 4.5-6.5 % magnesium, 1.8-2.2 % silicon, 0.5-0.7 % manganese, 0-0.25 % titanium, less than 1.0 % copper, less than 0.5 % iron and either 0.01-0.25 % in total or 0.01-0.25 % of each of one or more of zirconium, niobium, gadolinium, hafnium, yttrium, vanadium and/or chromium. Preferably the alloy comprises at least one minor alloying element selected from Zr, Nb, Gd, Hf, Ca, Y, Co, Ag, Au, Sb, Bi, Nd, Yb, V, Cr, Cu, Zn, Be and/or B, each in an amount less than 0.2 % and the total amount of titanium and minor alloying elements being less than 0.5 %. The alloy can be used to make aged castings and can be made by heating aluminium, silicon and manganese in elemental or alloy form to a temperature of at least 750 0C to form a melt, adding flux to the melt surface and subsequently adding magnesium which has been preheated to a temperature of at least 200 0C.

Description

ALLOY AND METHOD OF PRODUCTION THEREOF

FIELD OF THE INVENTION

The present invention relates to casting alloys and to a method of producing a casting alloy. In particular but not exclusively the invention relates to a casting alloy of high ductility.

BACKGROUND

Die-casting is a well-developed technical process by means of which parts may be manufactured from aluminium alloys. The quality of a die cast part depends on several factors including alloy composition and alloy processing. It is well known that the alloy composition is one of the most critical factors. Alloy composition influences significantly the castability. feeding behaviour and mechanical characteristics of the alloy and the service life of tools used in the casting process.

Aluminium die cast parts have achieved a particular significance in applications where high stress and high ductility are critical. One such example is the automobile industry where aluminium alloy die castings have been substituted for steel components for the purpose of weight reduction, especially for structural parts that can satisfy certain assembly process requirements such as riveting, welding and gluing. The increasing mechanical demands placed on aluminium die cast parts in the automobile industry have led to the use of special Al-Mg-Si alloys. Currently, the primary requirement of alloys used as structural parts in the automobile and airplane industries include (1) a yield strength at a level of at least of 15OMPa; (2) an ultimate strength at a level of at least 300MPa; (3) elongation at a level of at least 15%; and (4) appropriate corrosion resistance.

A number of prior art references disclose cast aluminium alloy compositions, including WO/2006/122341, WO/2005/047554, US 2005/0173032, EP 0 687 742 Al, AT 407 533 and EP 0 792 380.

It is against this background that the present invention has been conceived.

Embodiments of the invention may provide an aluminium alloy having improved strength and super-ductility. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.

STATEMENT OF THE INVENTION

Embodiments of the invention may be understood by reference to the appended claims.

Aspects of the invention provide an aluminium alloy, a casting, a component and a method of making an aluminium alloy.

In an aspect of the invention for which protection is sought there is provided an aluminium alloy comprising aluminium, from 4.5 to 6.5 wt% magnesium, from 1.8 to 2.2 wt% silicon, from 0.5 to 0.7 wt% manganese and from 0 to 0.25 wt% titanium.

Embodiments of the invention have the advantage that they enable super-ductile cast aluminium alloys suitable for use in demanding applications such as the automobile industry and aviation industry to be produced.

Furthermore, the applicant has noted that in some embodiments, advantageously the amount of Si may be decreased from 2.2 to 1.8 wt% as the amount of magnesium is increased from 4.5 to 6.5 wt %. Thus, the alloy may in some embodiments have around 4.5 wt% Mg and around 2.2 wt% Si, and in some alternative embodiments around 6.5 wt% Mg and around 1.8 wt % Si. Optionally the alloy has around 5.5 wt% Mg and around 2.0 wt% Si.

Optionally, the amount of magnesium is in the range from 4.5 to 5.5 wt% and the amount of Si is in the range from 2 to 2.2%.

Optionally, the amount of magnesium is in the range 5.5< Mg«=6.5 wt% and the amount of Si is in the range 1.8«=Sic2.0%.

Further optionally, the amount of magnesium is given by the equation (6.5-2x) wt% and the amount of silicon is given by the equation (1.8 + (x12.5)) wt% where 0«=x«=1.

Optionally the alloy may comprise one selected from gadolinium in the range from 0.01 to 0.2% and hafnium in the range from 0.05 to 0.lwt%.

The alloy may comprise substantially 0.6wt% manganese.

The alloy may comprise up to 0.15 wt% chromium.

Optionally the alloy further may comprise from 0.01 to 0.25 wt% of each of one or more grain refining alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), yttrium (Y), vanadium (V), and chromium (Cr).

Optionally the alloy may comprise a total amount from 0.01 to 0.25 wt% of one or more grain refining alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), yttrium (Y), vanadium (V), and chromium (Cr).

Thus, if the amounts of each of these elements are summed, the amount is in the range from 0.01 to 0.25wt%.

Optionally the amount of titanium and said one or more grain refining alloying elements is in the range from 0.01 to 0.25 wt%.

Optionally the amount of titanium is <0.2 wt% and the alloy comprises one or more minor alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), calcium (Ca), yttrium (Y), cobalt (Co), silver (Ag), gold (Au), antimony (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B), wherein the amount of said one or more minor alloying elements is individually less than 0.2%, the amount of titanium and the amount of said one or more minor alloying elements being totally less than 0.5%.

The alloy may comprise magnesium in the range from 4.5 to 6.5 wt%, silicon in the range from 1.5 to 2.5 wt%, manganese in the range from 0.4 to 0.8 wt% and titanium in the range from 0.10 to 0.25 wt%.

Advantageously the alloy may have less than 0.5 wt% iron.

Further advantageously the alloy may have less than 0.3 wt% iron.

The alloy may contain less than 1.0 wt% copper.

Advantageously the alloy may contain less than 0.5 wt% copper.

Advantageously the alloy may be suitable for die casting and related casting process.

In one aspect of the invention for which protection is sought there is provided a casting comprising an alloy according to another aspect.

The casting may be an aged casting.

In a further aspect of the invention for which protection is sought there is provided a motor vehicle component comprising a casting according to an aspect of the invention.

In a still further aspect of the invention for which protection is sought there is provided a method of forming an aluminium alloy comprising aluminium, from 4.5 to 6.5 wt% magnesium, from 1.8 to 2.2 wt% silicon, from 0.5 to 0.7 wt% manganese and from 0 to 0.25 wt% titanium in either elemental or alloy form comprising the step of heating aluminium, silicon and manganese to a temperature at or above 750°C to form a melt, subsequently adding magnesium and optionally titanium.

Advantageously the step of adding magnesium may comprise adding magnesium preheated to a temperature of at least 200°C.

The step of adding magnesium may be preceded by the step of adding a flux to a surface of the melt.

The method may comprise the step of subsequently agitating the melt to promote dissolution of the magnesium.

The method may comprise the step of subsequently waiting for a prescribed period, optionally at least 5 minutes thereby to allow time for the melt to homogenize.

Advantageously the method may comprise the step of adding to the melt titanium or a titanium alloy.

Further advantageously the titanium or titanium alloy may be preheated to a temperature of at least 200°C before being added to the melt.

The step of adding to the melt titanium or a titanium alloy may comprise adding titanium or a titanium alloy below the flux.

The method may comprise the step of subsequently agitating the melt to promote dissolution of the titanium.

Advantageously the method may comprise the step of degassing the melt of hydrogen by means of nitrogen, Ar or any other suitable gas.

The method may comprise de-gassing the melt of hydrogen to a pre-determined level of hydrogen in the melt.

In a further aspect of the invention for which protection is sought there is provided a die castable Al-Mg-Si type alloy with improved balance of excellent stiength and super ductility.

Alloy according to embodiments of the invention represents a substantial improvement over standaid Al-Mg-Si type alloys such as UK LM5.

Alloy according to some embodiments of the invention is suitable for forming aluminium components in the automobile industiy. Such components aie required to satisfy high strength and supei ductility requirements. Embodiments of the invention allow the scope of the application of aluminium components in the automobile industry to be expanded.

Some embodiments of the invention foi which piotection is sought provide an aluminium alloy having desired strength and ductility in the cast state, so that solution heat treatment of the cast parts and with its associated disadvantages can be avoided. In some embodiments mechanical properties of an aluminium alloy may be enhanced by short-teim ageing at relatively low temperature and/oi an ageing treatment as part of a manufacturing piocess of a component, such as paint baking, which does not affect dimensions of a casting.

It is believed that the improved balance of properties made available by some embodiments of the invention, paiticulaily the properties of highei strength and super ductility, results from the balanced combination of the alloying elements Mg, Si, Mn and the minor addition of one or more special elements in the prescribed ranges.

It is believed that magnesium is the primary strengthening element in the alloy. Mg levels above 3.0 wt% provide the required mechanical properties. It is to be understood that in some embodiments the amount of Mg should not exceed 8.0 wt% in order to ensure an acceptable ductility.

In some embodiments the Mg content in the alloy is more than 4.5 wt% and less than 6.5 wt% in order to provide an alloy having an improved balance of tensile strength, yield strength and ductility as measured by elongation of a test sample.

Si is another primary alloying element. It is believed that Si combines with Mg to form Mg2Si, strengthening the alloy. Si is included primarily for the improvement of castability and reduces casting defects in die casting including hot tearing and inclusions. However, the increased Si content is believed to reduce the ductility of a casting. As such, the amount of Si level is kept in the range from 0.7 to 4 wt%. In some embodiments the amount of Si is kept between 1.5 to 2.5 wt%.

Mn is also an important additive element for die casting. It is believed that Mn combines with Fe to alter the morphology of Fe-containing compounds from a needle-like morphology to a nodular morphology, reducing the harmful effect of Fe. Mn can also reduce the tendency of a die to stick to die cast parts. In embodiments of the present invention Mn content is in the range from 0.1 to 1.5 wt%.

In some embodiments the amount of Mn is between 0.4 to 0.8 wt%, thereby providing a balance between a requirement for sufficient process control and a requirement for a good combination of strength and ductility.

The present inventors have recognised that it is desirable to ensure that Fe is not present in an amount of 0.3 wt% or more. This is at least in part because it is believed that Fe is an unavoidable detrimental element in diecasting in terms of mechanical properties and corrosion resistance where Fe or Fe-containing dies and tools are employed. As noted above, Fe may form Fe-containing compounds of needle-like shape during die casting, which may initiate cracking and failure of cast components.

In some embodiments, in order to provide required mechanical properties of the alloy, in particular to improve the ductility of the alloy, the amount of Fe is kept below 0.1 wt%.

In some alternative embodiments, addition of Fe and/or Mn may be desirable for die casting in order to reduce adhesion of a die cast part to a mould.

Advantageously, in some embodiments the sum of the Mn and Fe content of an alloy is at least 0.7 wt%.

Further advantageously, the Mn content may be at least double that of Fe. However, it is believed to be particularly advantageous for the die cast alloy to contain either only Fe or only Mn in some embodiments.

Ti has been found to act as a grain refiner during solidification of a casting of an alloy according to some embodiments of the invention. Ti has been found to have a grain refining effect at concentrations of less than 0.4 wt%. Advantageously in some embodiments the concentration of Ti is less than 0.25 wt%. In some embodiments the concentration of Ti is in the range from 0.01 wt% to 0.25 wt% or from 0.01 wt% to 0.4 wt%.

In some embodiments Ti may be replaced in part or in whole by zirconium (Zr) and/or niobium (Nb) and/or gadolinium (Gd) and/or yttrium (Y) and/or vanadium (V) and/or chromium (Cr) with a total amount being in the same compositional range as that of Ti described above. In some embodiments it is found that a similar effect is achieved to that when Ti is used. Other elements or combinations thereof may also be useful as grain refiners in addition or instead in some embodiments.

In some embodiments, a small amount of copper may increase the yield strength of the alloy whilst reducing the ductility of the alloy.

It is to be understood that, normally in the art, a deliberate Cu addition is avoided if subsequent ageing or processing is not a preferred option to improve the yield strength.

Advantageously, the amount of Cu does not exceed 0.5 wt%.

It is to be understood that in some embodiments an alloy may comprise one or more elements that may act as a grain refiner, act as an alloying element, and/or be present as an impurity. In some embodiments the amount of any such element is a maximum of 0.3 wt% and totally such elements may be in an amount that is less than 0.5%. The one or more elements may be selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), calcium (Ca), yttrium (Y), silver (Ag), gold (Au), antinomy (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B).

Certain embodiments of the present invention may be further understood by reference to the following specific examples. These examples and the terminology used herein are for the purpose of describing particular embodiments only and are not intended to be limiting.

In one embodiment of the invention an alloy is provided that has the following composition: o magnesium 3.0 to 8 wt%, o silicon 0.7 to 4.0 wt%, o manganese 0.1 to 1.5 wt%, o iron up to 0.35 wt%, a titanium or the other grain refining elements 0.02 to 0.3 wt%, and o impurity and minor alloying elements at a level of maximum 0.3 wt% and totally <0.5 wt% of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), gadolinium (Gd), calcium (Ca), yttrium (Y), silver (Ag), gold (Au), antimony (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B), o and the remainder aluminium.

In a further embodiment the alloy according to the invention has the following composition: o magnesium 4.5 to 6.5 wt%, o silicon 1.5 to 2.5% wt%, o manganese 0.4 to 0.8 wt%, o ironuptoo.lwt%, a titanium or the other grain refining elements 0.1 to 0.25 wt%, o impurity and minor alloying elements at a level of a maximum of 0.2 wt% and totally <0.3 wt% of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), gadolinium (Gd), calcium (Ca), yttrium (Y), silver (Ag), gold (Au), antimony (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B), a and the remainder aluminium.

In an aspect of the invention for which protection is sought there is piovided an aluminium alloy comprising trom 3.0 to 8.0 wt% magnesium, from 0.7 to 4.0 wt% silicon, from 0.1 to 1.5 wt% manganese and up to 0.3 wt% iron.

Within the scope of this application it is envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination thereof. For example, features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

DETAILED DESCRIPTION

In one embodiment, aluminium alloy and the resultant casting can be produced as follows: 1) Providing each element in the required ratio from either pure metal ingots or master alloy ingots; 2) Heating Al, Si, Mn (optionally in the form of substantially pure metal ingots or master alloy ingots) in a crucible to a temperature of at least 750°C to form a melt; 3) Removing slugs on the surface of the melt, subsequently adding a flux to the surface of the melt; 4) Adding to the melt Mg (optionally in ingot form) that has been preheated to a temperature of at least 200°C, the Mg being provided below the flux, and stirring the melt vigorously to assist dissolution of the Mg into the melt; 5) Waiting for at least 5 minutes to allow the melt in the crucible to become homogenized; 5) Adding to the melt Ti-containing alloy, optionally in master alloy ingot form, that has been preheated at a temperature at least 200°C; 7) Holding the melt at a temperature of at least 50°C above its liquidus and removing periodically slugs that may form on the melt; B) Degassing the melt of H2 by means of N2, Ar or other suitable gas to a pre-requested level of H2 in the melt, and measuring the H2 level in the melt; 9) Measuring the chemical composition of the alloy made by the melt in the crucible, and adjusting the chemical composition by adding required elements into the melt to achieve a required amount of each element; 10) Maintaining the melt at a temperature required for die casting, for example a temperature of around 100°C above the liquidus; 11) Loading the melt into a shot sleeve of a die caster, having mounted a preheated die held at a temperature above 150°C; 12) Operating the die caster to introduce the melt into the die cavity, cooling the melt down under pressure to form a casting, and releasing the casting from the die.

Tensile tests were conducted on cast samples of aluminium alloy produced by the method described above using metal in ingot form. The cast samples were tested according to the Standard Test Method described in ASTM B557M -10. The results of the tensile tests carried out are listed in Table 1. Each of the alloys listed (tests 1 to 8) are alloys according to embodiments of the invention.

Tensile Yield Breaking Table I strength strength elongation (MPa) (MPa) (%) 1 AIMg5Si2Mn + 0.2%Ti 312 160 17.4 2 AlMg5Si1.5Mn + 0.2%Ti 293 153 18.6 3 AIMg5S6 Mn + 0.2%Ti-'-0.2%Cu 302 174 13.8 4 AIMg45Si2Mn + 0.2%Ti 287 137 15.5 AIMg5Si1Mn + 0.2%Ti 298 140 17.8 6 AIMg5Si1Mn + 0.1%Ti +0.1%Zr 291 141 16.9 7 AIMg5Si2Mn +0.1%Ti 289 154 16.1 8 AIMg5Si2Mn 284 145 12.8 As it can be seen from the table, the adding of titanium or titanium and zirconium can result in a significant increase in breaking elongation compared with a corresponding alloy not containing either of these elements (test 8). The alloys are capable of meeting the basic requirement for structural components used in automobile and airplane industry.

Further samples of alloy according to the present invention having Al, Mg, Si and Mn in the ratio 100:5:1.5:0.6 were then prepared, with different amounts of additional Ti and Cu elements. The samples were subjected to an ageing treatment in which the samples were heat treated at 180°C for 30 minutes or 60 minutes without further protection in the furnace.

It is to be understood that this ageing temperature corresponds to that used in the automobile industry for curing paint after it has been applied to an aluminium alloy component of the kind that might be manufactured from an alloy according to an embodiment of the invention. The time periods also correspond to upper and lower limits of those that might be used to cure paint in a typical curing process.

The aged samples were then subject to an identical tensile testing procedure to that which the samples listed in Table 1 were subjected. The results of the tensile tests carried out on the aged samples are listed in Table 2.

Tensile Yield Breaking Table 2 strength strength elongation (MPa) (MPa) (%) 1 AIMg5Si15Mn + 0.2%Ti @30mm 303 158 16.7 2 AIMg5Si15Mn + 0.2%Ti+0.2%Cu @30mm 306 180 13.5 3 AIMg5Si1.5Mn + 0.2%Ti @60mm 312 166 15.1 4 AIMg5Si1.5Mn + 0.2%Ti+0.2%Cu @60mm 318 188 12.8 It is apparent from Table 2 that short term ageing can improve the properties of the alloys.

The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting.

Embodiments of the invention may be described with reference to the following numbered paragraphs: 1. An aluminium alloy comprising from 3.0 to 8.0 wt% magnesium, from 0.7 to 4.0 wt% silicon, from 0.1 to 1.5 wt% manganese and up to 0.3 wt% iron.

2. An alloy as disclosed in paragraph 1, with grain refiners of maximum of 0.25 wt%.

3. An alloy as disclosed in paragraph 1 or paragraph 2 comprising one or more minor alloying elements to an individual maximum of 0.2 wt% and totally <0.5 wt%, the one or more alloying elements being at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), gadolinium (Gd), calcium (Ca), yttrium (Y), cobalt (Co),silver (Ag), gold (Au), antinomy (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B).

4. The alloy as disclosed in paragraph 1, wherein the amount of magnesium is in the range from 4.5 to 6.5 wt%, the amount of silicon is in the range from 1.5 to 2.5 wt%, the amount of manganese is in the range from 0.4 to 0.8 wt%, the alloy further comprising 0.10 to 0.25 wt% titanium.

5. The super ductile cast aluminium alloy as disclosed in any preceding paragraph having less than 0.5 wt% iron.

6. The super ductile cast aluminium alloy according to an alloy as disclosed in any one of paragraphs ito 4 having less than 0.15 wt% iron.

7. An alloy as disclosed in any one of paragraphs 1 to 6, wherein the alloy contains <1.0 wt% copper.

8. An alloy as disclosed in any one of paragraphs 1 to 6, wherein the alloy contains <0.5 wt% copper.

9. The super ductile cast aluminium alloy of paragraph 1, wherein the alloy contains <0.4 wt% zirconium (Zr).

10. The super ductile cast aluminium alloy of paragraph 1, wherein the alloy contains <0.2 wt% zirconium (Zr).

11. The super ductile cast aluminium alloy of paragraph 1, wherein the alloy contains at least 0.001 wt% vanadium (V).

12. The super ductile cast aluminium alloy of paragraph 1, wherein the alloy contains at least 0.008 wt% vanadium (V).

13. The super ductile cast aluminium alloy of paragraph 1, wherein the alloy contains at least 0.001 wt% gadolinium (Gd).

14. The super ductile cast aluminium alloy of paragraph 1, wherein the alloy contains at least 0.001 wt% chromium (Cr).

15. The super ductile cast aluminium alloy of paragraph 1, wherein the alloy contains <0.5 wt% zinc (Zn).

16. The super ductile cast aluminium alloy of any of paragraphs ito 15, wherein the alloy is for die casting and related casting process.

17. The super ductile cast aluminium alloy of any of paragraphs ito 15, wherein the alloy is used in as cast state and short term ageing can enhance its property.

18. A super ductile cast aluminium alloy, comprising 3.0 to 8.0 wt% magnesium, 0.7 to 4.Owt.% silicon, 0.1 to 1.5 wt% manganese, and the remainder of aluminium, and impurities of maximum 0.3 wt% iron, with grain refiners of maximum of 0.25 wt% and with minor alloying elements to an individual maximum of 0.2 wt% and totally <0.5 wt% of at least one element selected from titanium (Ti), zirconium (Zr), niobium (Nb), gadolinium (Gd), calcium (Ca), yttrium (Y), cobalt (Co),silver (Ag), gold (Au), antinomy (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B).

19. The aluminium alloy according to paragraph 18, comprising: magnesium 4.5 to 6.5 wt%, silicon 1.5 to 2.5 wt%, manganese 0.4 to 0.8 wt%, titanium 0.10 to 0.25 wt%.

Some embodiments of the present invention may be further understood with reference to the following numbered paragraphs: 1. An aluminium alloy comprising aluminium, from 3.0 to 8.0 wt% magnesium, from 0.7 to 4.0 wt% silicon, from 0.1 to 1.5 wt% manganese and from 0 to 0.25 wt% titanium.

2. An alloy as described in paragraph 1, further comprising up to 0.25 wt% of one or more grain refining alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), yttrium (Y), vanadium (V), and chromium (Cr).

3. An alloy as described in paragraph 2 wherein the amount of titanium and said one or more grain refining alloying elements is from 0.01 to 0.25 wt%.

4. An alloy as described in paragraph 1 wherein the amount of titanium is <0.2 wt% and the alloy comprises one or more minor alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), calcium (Ca), yttrium (Y), cobalt (Co),silver (Ag), gold (Au), antimony (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B), wherein the amount of said one or more minor alloying elements is individually less than 0.2%, the amount of titanium and the amount of said one or more minor alloying elements being totally less than 0.5%.

5. An alloy as described in any preceding paragraph, comprising magnesium in the range from 4.5 to 6.5 wt%, silicon in the range from 1.5 to 2.5 wt%, manganese in the range from 0.4 to 0.8 wt% and titanium in the range from 0.10 to 0.25 wt%.

6. An alloy as described in any preceding paragraph having less than 0.5 wt% iron.

7. An alloy as described in any preceding paragraph having less than 0.3 wt% iron.

8. An alloy as described in any preceding paragraph, containing less than 1.0 wt% copper.

9. An alloy as described in any preceding paragraph, containing less than 0.5 wt% copper.

10. An alloy as described in any preceding paragraph suitable for die casting and related casting processes.

11. A casting comprising an alloy as described in any preceding paragraph.

12. An aged casting as described in paragraph 11.

13. A motor vehicle component comprising a casting as described in paragraph 11 or paragraph 12.

14. A method of forming an aluminium alloy comprising from 3.0 to 8.0 wt% magnesium, from 0.7 to 4.0 wt% silicon, from 0.1 to 1.5 wt% manganese and from 0 to 0.25 wt% titanium comprising the step of heating aluminium! silicon and manganese to a temperature at or above 750°C to form a melt, subsequently adding magnesium and optionally titanium.

15. A method as described in paragraph 14 wherein the step of adding magnesium comprises adding magnesium preheated to a temperature of at least 200°C.

16. A method as described in paragraph 15 wherein the step of adding magnesium is preceded by the step of adding a flux to a surface of the melt.

17. A method as described in paragraph 15 or 16 comprising the step of subsequently agitating the melt to promote dissolution of the magnesium.

18. A method as described in any one of paragraphs 14 to 17 comprising the step of subsequently waiting at least 5 minutes thereby to allow time for the melt to homogenize.

19. A method as described in any one of paragraphs 14 to 18 comprising the step of adding to the melt titanium or a titanium alloy.

20. A method as described in paragraph 19 wherein the titanium or titanium alloy is preheated to a temperature of at least 200°C before being added to the melt.

21. A method as described in paragraph 19 or paragraph 20 depending through paragraph 16 wherein the step of adding to the melt titanium or a titanium alloy comprises adding titanium or a titanium alloy below the flux.

22. A method as described in any one of paragraphs 19 to 21 comprising the step of subsequently agitating the melt to promote dissolution of the titanium.

23. A method as described in any one of paragraphs 19 to 22 comprising the step of subsequently waiting at least 5 minutes thereby to allow time for the melt to homogenize.

24. A method as described in any one of paragraphs 14 to 23 comprising the step of degassing the melt of H2 by means of N2, Ar or any other suitable gas.

25. A method as described in paragraph 24 comprising de-gassing the melt of H2 to a pie-determined level of H2 in the melt.

Still further embodiments of the present invention may be understood with reference to the following numbered paragraphs: 1. An aluminium alloy comprising aluminium, from 4.5 to 6.5 wt% magnesium, from 1.8 to 2.2 wt% silicon, from 0.5 to 0.7 wt% manganese and from 0 to 0.25 wt% titanium.

2. An alloy as described in paragraph 1 wherein the amount of magnesium is in the range from 4.5 to 5.5 wt% and the amount of Si is in the range from 2 to 2.2%.

3. An alloy as described in paragraph 1 wherein the amount of magnesium is in the range 5.5< Mg«=6.5 wt% and the amount of Si is in the range 1.8«=Si<2.0%.

4. An alloy as described in paragraph 1 wherein the amount of magnesium is given by the equation (6.5-2x) wt% and the amount of silicon is given by the equation (1.8 + (x12.5)) wt% where 0«=x«=1.

5. An alloy as described in any preceding paragraph comprising one selected from gadolinium in the range from 0.01 to 0.2% and hafnium in the range from 0.05 to 0.lwt%.

6. An alloy according to any preceding paragraph comprising substantially 0.6wt% manganese.

7. An alloy according to any preceding paragraph comprising up to 0.15 wt% chromium.

8. An alloy as described in any preceding paragraph, comprising from 0.01 to 0.25 wt% of each of one or more grain refining alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), yttrium (Y), vanadium (V), and chromium (Cr).

9. An alloy as described in any one of paragraphs 1 to 7 comprising a total amount from 0.01 to 0.25 wt% of one or more grain refining alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), yttrium (Y), vanadium (V), and chromium (Cr).

Thus, if the amounts of each of these elements is summed, the amount is in the range from 0.01 to 0.25wt%.

10. An alloy as described in any preceding paragraph wherein the amount of titanium and said one or more grain refining alloying elements is from 0.01 to 0.25 wt%.

11. An alloy as described in any one of paragraphs 1 to 9 wherein the amount of titanium is <0.2 wt% and the alloy comprises one or more minor alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), calcium (Ca), yttrium (Y), cobalt (Co),silver (Ag), gold (Au), antimony (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), beryllium (Be) and boron (B), wherein the amount of said one or more minor alloying elements is individually less than 0.2%, the amount of titanium and the amount of said one or more minor alloying elements being totally less than 0.5%.

12. An alloy as described in any one of paragraphs ito 9, containing less than 1.0 wt% copper.

13. An alloy as described in paragraph 12, containing less than 0.5 wt% copper.

14. An alloy as described in any preceding paragraph having less than 0.5 wt% iron.

15. An alloy as described in any preceding paragraph having less than 0.3 wt% iron.

16. A casting comprising an alloy as described in any preceding paragraph.

17. An aged casting as described in paragraph 16.

18. A motor vehicle component comprising a casting as described in paragraph 16 or paragraph 17.

19. A method of forming an aluminium alloy comprising aluminium, from 4.5 to 6.5 wt% magnesium, from 1.8 to 2.2 wt% silicon, from 0.5 to 0.7 wt% manganese and from 0 to 0.25 wt% titanium comprising the step of heating aluminium, silicon and manganese in either elemental or alloy form to a temperature at or above 750°C to form a melt, subsequently adding magnesium and optionally titanium.

20. A method as described in paragraph 19 wherein the step of adding magnesium comprises adding magnesium preheated to a temperature of at least 200°C.

21. A method as described in paragraph 20 wherein the step of adding magnesium is preceded by the step of adding a flux to a surface of the melt.

22. A method as described in paragraph 20 or 21 comprising the step of subsequently agitating the melt to promote dissolution of the magnesium.

23. A method as described in any one of paragraphs 19 to 22 comprising the step of subsequently waiting for a prescribed period, optionally at least 5 minutes, thereby to allow time for the melt to homogenize.

24. A method as described in any one of paragraphs 19 to 23 comprising the step of adding to the melt titanium or a titanium alloy.

25. A method as described in paragraph 24 wherein the titanium or titanium alloy is preheated to a temperature of at least 200°C before being added to the melt.

26. A method as described in paragraph 24 or paragraph 25 depending through paragraph 21 wherein the step of adding to the melt titanium or a titanium alloy comprises adding titanium or a titanium alloy below the flux.

27. A method as described in any one of paragraphs 24 to 26 comprising the step of subsequently agitating the melt to promote dissolution of the titanium.

28. A method as described in any one of paragraphs 24 to 27 comprising the step of subsequently waiting for a prescribed period, optionally at least 5 minutes thereby to allow time for the melt to homogenize.

29. A method as described in any one of paragraphs 19 to 28 comprising the step of degassing the melt of H2 by means of N2, Ar or any other suitable gas.

30. A method as described in paragraph 29 comprising de-gassing the melt of H2 to a pre-determined level of H2 in the melt.

Throughout the description and claims of this specification, the words "comprise' and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS: 1. An aluminium alloy comprising aluminium! from 4.5 to 6.5 wt% magnesium, from 1.8 to 2.2 wt% silicon, from 0.5 to 0.7 wt% manganese and from 0 to 0.25 wt% titanium.
2. An alloy as claimed in claim 1 wherein the amount of magnesium is in the range from 4.5 to 5.5 wt% and the amount of Si is in the range from 2 to 2.2%.
3. An alloy as claimed in claim 1 wherein the amount of magnesium is in the range 5.5< Mg«=6.5 wt% and the amount of Si is in the range 1.8«=Si<2.0%.
4. An alloy as claimed in claim 1 wherein the amount of magnesium is given by the equation (6.5-2x) wt% and the amount of silicon is given by the equation (1.8 + (x/2.5)) wt% where 0«=x«=1.
5. An alloy as claimed in any preceding claim comprising one selected from gadolinium in the range from 0.01 to 0.2% and hafnium in the range from 0.05 to 0.lwt%.
6. An alloy according to any preceding claim comprising substantially 0.6wt% manganese.
7. An alloy according to any preceding claim comprising up to 0.15 wt% chromium.
8. An alloy as claimed in any preceding claim, comprising from 0.01 to 0.25 wt% of each of one or more grain refining alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf). yttrium (Y), vanadium (V), and chromium (Cr).
9. An alloy as claimed in any one of claims 1 to 7 comprising a total amount trom 0.01 to 0.25 wt% of one or more grain refining alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), yttrium (Y), vanadium (V), and chromium (Cr).
10. An alloy as claimed in any preceding claim wherein the amount of titanium and said one or more grain refining alloying elements is from 0.01 to 0.25 wt%.
11. An alloy as claimed in any one of claims ito 9 wherein the amount of titanium is <0.2 wt% and the alloy comprises one or more minor alloying elements selected from zirconium (Zr), niobium (Nb), gadolinium (Gd), hafnium (Hf), calcium (Ca), yttrium (Y), cobalt (Co),silver (Ag), gold (Au), antimony (Sb), bismuth (Bi), neodymium (Nd), ytterbium (Yb). vanadium (V), chromium (Cr), copper (Cu), zinc (Zn). beryllium (Be) and boron (B), wherein the amount of said one or more minor alloying elements is individually less than 0.2%, the amount of titanium and the amount of said one or more minor alloying elements being totally less than 0.5%.
12. An alloy as claimed in any one of claims ito 9, containing less than 1.0 wt% copper.
13. An alloy as claimed in claim 12, containing less than 0.5 wt% copper.
14. An alloy as claimed in any preceding claim having less than 0.Swt% iron.
15. An alloy as claimed in any preceding claim having less than 0.3 wt% iron.
16. A casting comprising an alloy as claimed in any preceding claim.
17. An aged casting as claimed in claim 16.
18. A motor vehicle component comprising a casting as claimed in claim 16 or claim 17.
19. A method of forming an aluminium alloy comprising aluminium, from 4.5 to 6.5 wt% magnesium, from 1.8 to 2.2 wt% silicon, from 0.5 to 0.7 wt% manganese and from 0 to 0.25 wt% titanium comprising the step of heating aluminium, silicon and manganese in either elemental or alloy form to a temperature at or above 750°C to form a melt, subsequently adding magnesium and optionally titanium.
20. A method as claimed in claim 19 wherein the step of adding magnesium comprises adding magnesium preheated to a temperature of at least 200°C.
21. A method as claimed in claim 20 wherein the step of adding magnesium is preceded by the step of adding a flux to a surface of the melt.
22. A method as claimed in claim 20 or 21 comprising the step of subsequently agitating the melt to promote dissolution of the magnesium.
23. A method as claimed in any one of claims 19 to 22 comprising the step of subsequently waiting for a prescribed period, optionally at least 5 minutes, thereby to allow time for the melt to homogenize.
24. A method as claimed in any one of claims 19 to 23 comprising the step of adding to the melt titanium or a titanium alloy.
25. A method as claimed in claim 24 wherein the titanium or titanium alloy is preheated to a temperature of at least 200°C before being added to the melt.
26. A method as claimed in claim 24 or claim 25 depending through claim 21 wherein the step of adding to the melt titanium or a titanium alloy comprises adding titanium or a titanium alloy below the flux.
27. A method as claimed in any one of claims 24 to 26 comprising the step of subsequently agitating the melt to promote dissolution of the titanium.
28. A method as claimed in any one of claims 24 to 27 comprising the step of subsequently waiting for a prescribed period, optionally at least 5 minutes thereby to allow time for the melt to homogenize.
29. A method as claimed in any one of claims 19 to 28 comprising the step of degassing the melt of H2 by means of N2, Ar or any other suitable gas.
30. A method as claimed in claim 29 comprising de-gassing the melt of H2 to a pre-determined level of H2 in the melt.
31. An alloy, a casting, a motor vehicle component or a method substantially as hereinbefore described.