WO2016034857A1

WO2016034857A1 - A casting al-mg-zn-si based aluminium alloy for improved mechanical performance

Info

Publication number: WO2016034857A1
Application number: PCT/GB2015/052478
Authority: WO
Inventors: Shouxun Ji; Zhongyun Fan
Original assignee: Brunel University London
Current assignee: Brunel University London
Priority date: 2014-09-01
Filing date: 2015-08-27
Publication date: 2016-03-10
Anticipated expiration: 2017-03-01
Also published as: GB201415420D0; WO2016034857A4; EP3189173A1

Abstract

A casting Al-Mg-Zn-Si based aluminium alloy material for providing improved mechanical performance, includes the following components: greater than 7.0 and up to 15.0wt-% of magnesium, greater than 1.8 and up to 7.0wt-% of zinc, greater than 1.5 and up to 5.0wt-% of silicon, from 0.05 to 2.0wt-% of manganese, and additionally at least one element from 0 to 0.5 wt-% beryllium, 0 to 2. wt-% calcium, 0 to 1.5 wt-% strontium, 0 to 1.0wt-% titanium, 0 to 1.5wt-% copper, 0 to 0.5wt-% boron, 0 to 1.0wt-% scandium and 0 to 2.0wt-% rare earth elements, and the reminder of the alloy is aluminium and inevitable impurities.1

Description

A Casting Al-Mg-Zn-Si Based Aluminium Alloy

for Improved Mechanical Performance

The present application relates to a casting aluminium alloy, in particular to a Al- Mg-Zn-Si based alloy that can provide the improved mechanical properties, typically over 300MPa of yield strength and over 420MPa of ultimate tensile strength with over 6% of elongation at fracture.

Aluminium alloys are currently the most promising lightweight materials used in transportation to achieve weight reduction for improving fuel efficiency and reducing CO2 emissions. The increased strength and other mechanical properties are useful to make components with thinner wall thickness and therefore lighter weight, which is critical to satisfy the demands of structural components made by casting Al-alloys. However, conventional casting aluminium alloys normally provide the mechanical properties of (a) ultimate tensile strength (UTS) less than 250 MPa, (b) elongation at fracture less than 10 % and (c) 0.2% yield strength less than 200 MPa. Therefore there is a demand for casting aluminium alloys to make casting products with improved mechanical properties, in particular high strength with satisfied elongation at fracture. It would be attractive to develop a high strength aluminium alloy that can provide UTS over 420MPa and 0.2% yield strength over 300MPa with elongation at fracture over 6%.

Prior attempts to provide improved mechanical properties of casting aluminium alloys have been patented from different aspects. In EP2000031 1378, a high strength dispersion strengthened aluminium alloy comprising an aluminium solid solution matrix strengthened by a dispersion of particles based on the compound AI3X, where AI3X has an L12 structure, is described. Various alloying elements are employed to modify the lattice parameter of the matrix and/or the particles so that the matrix and particles have similar lattice parameters. The alloy is produced by rapid solidification from the melt. The element X is selected from the group consisting of Sc, Er, Lu, Yb, Tm and U, and mixtures thereof and further containing Ti, Nb, V, Zr, and Cr in amounts insufficient to cause the formation of more than about 5 vol % of non L12 structure phases and wherein the aluminium solid solution matrix contains at least one element selected from the group consisting of Mg, Ag, Zn, Li, Cu and mixtures thereof. However, this patent did not clarify how the rapid solidification is achieved and how the forming process is carried out after rapid solidification. This means that it is not possible for casting shaped

components.

European Patent Application EP0819778 described a high-strength and high thermal resistance aluminium-based alloy consisting essentially of a composition represented by the general formula: AlbalMnaMb or AlbalMnaMbTMc wherein M represents one or more members selected from the group consisting of Ni, Co, Fe and Cu, TM represents one or more members selected from the group consisting of Ti, V, Cr, Y, Zr, La, Ce and Mm and a, b and c each represent an atomic percent (at %) in the range of 2 <a < 5, 2 < b < 6 and 0 < c < 2 and containing monoclinic crystals of an intermetallic compound of an AI9Co2-type structure in the structure thereof. The Al-based alloy has excellent mechanical properties including a high hardness, high strength and high elongation at evaluated temperature.

European Patent Application EP2072628 described a high strength crash resistant wrought aluminium alloy extruded or forged product having a high impact resistance, the aluminium alloy comprising, in wt.%: Si 0.5 to 0.95, Mg 0.6 to 0.95, Mn 0.1 to 0.3, V 0.05 to 0.25, Ni 0.05 to 0.25, Cu maximum 0.3,optionally one or two element(s) selected from the group consisting of: (Cr 0.05 to 0.2, and Zr 0.05 to 0.2), Zn< 0.2, Fe < 0.5, Ti < 0.1 , inevitable impurities and balance aluminium. European Patent Application EP0569000 described a high strength and high toughness aluminium alloy produced by crystallization of one of two aluminium alloy blanks: one having a metallographic structure with a volume fraction Vf of a mixed-phase texture consisting of an amorphous phase and an aluminium crystalline phase being equal to or more than 50 % (Vf > 50 %), and the other having a metallographic structure with a volume fraction Vf of an amorphous single-phase texture being equal to or more than 50 % (Vf > 50 %). The aluminium alloy is represented by a chemical formula: Al, X, Z, Si, wherein X is at least one element selected from the group consisting of Mn, Fe, Co and Ni; Z is at least one element selected from the group consisting of Zr and Ti.

PCT Application WO/2010/003349 disclosed a high strength casting aluminium alloy material comprises (in weight %) Cu 2.0-6.0%, Mn 0.05-1 .0%, Ti 0.01 -0.5% , Cr 0.01 -0.2%, Cd 0.01 -0.4%, Zr 0.01 -0.25%, B 0.005-0.04%, rare earth 0.05- 0.3%, and balance aluminium and trace impurities. The alloy is based on copper strengthening and has high rare earth content.

European Patent Application EP2548983 provided a wrought aluminium alloy exhibiting a sufficient heat resistance, tensile strength as well as stress corrosion cracking resistance necessary for use as automobile parts. Also, provided are a forged part forged from such aluminium alloy and an aluminium alloy high strength bolt made thereof. The aluminium alloy (by mass) consists of (by mass) 1 .0 to 1 .7% of Si, 0.05 to 0.5% of Fe, 0.8 to 1 .5% of Cu, 0.6 to 1 .2% of Mn, 0.9 to 1 .5% of Mg, 0.05 to 0.5% of Zn, 0.05 to 0.3% of Zr, 0.01 to 0.2% of V, and when needed, Ti exceeding 0% and not more than 0.05%, and, when further needed, Ni exceeding 0% and not more than 0.7%, the remainder being Al and unavoidable impurities.

European Patent Application EP1347066 disclosed a high-strength aluminium alloy for casting comprising 3.5 to 4.3 % of Cu, 5.0 to 7.5 % of Si, 0.10 to 0.25 % of Mg, not more than 0.2 % of Fe, 0.0004 to 0.0030 % of P, 0.005 to 0.0030 % of Sr, and the balance comprising Al and unavoidable impurities. A high-strength cast aluminium alloy is also disclosed obtained by: casting a high-strength aluminium alloy for casting comprising 3.5 to 4.3 % of Cu, 5.0 to 7.5 % of Si, 0.10 to 0.25 % of Mg, not more than 0.2 % of Fe, 0.0004 to 0.0030 % of P, 0.005 to 0.030 % of Sr, 0.05 to 0.35 % of Ti, and the balance comprising Al and unavoidable impurities; and subjecting the alloy thus cast to a T6 treatment. The claimed best results were that the cast alloy exhibited a tensile strength of not less than 383 MPa, elongation of not less than 9.9 %, 0.2% proof strength of not less than 223 MPa.

EP-A-0918095 disclosed a structural component made of an aluminium die- casting alloy, consisting of, in weight percent: Si< 0.5, Fe< 1 .0, Mn0.1 to 1 .6, Mg< 5.0, Ti< 0.3, Zn<0.1 Sc0.05 to 0.4 and optional Zr 0.1 to 0.4, balanced aluminium and impurities. By the addition of the very expensive Sc in a range of 0.05 to 0.4% and optionally in combination with Zr in a range of 0.1 to 0.4% and the requirement of an heat treatment in the range of 230 to 350 DEG C following the die-casting of the structural component a yield strength of about 120 MPa, a tensile strength of 180 MPa and an elongation at fracture of 16% is obtained.

EP-A-0908527 disclosed a casting aluminium alloy, in particular suitable as a die- casting alloy, consisting of, in weight percent: Mg2.0 - 3.3, SiO.15 - 0.35, Mn0.2 - 1 .0, Fe< 0.20, Cu< 0.05, Cr< 0.05, Zn< 0.10, Be< 0.003, Ti< 0.20, Ce< 0.80 with balance aluminium and impurities. This casting alloy is capable of achieving yield strength of more than 100 MPa and an elongation of more than 14%. Further the die-sticking of the alloy in a die-casting operation can be reduced by replacing part of the Mn by more expensive Ce.

WO-A-00/17410 disclosed an aluminium die-casting alloy, consisting of, in weight percent: Mg2.5 - 4.0, Mn1.0 - 2.0, Fe< 0.60, preferably 0.25 - 0.60, Si< 0.45, preferably 0.20 - 0.45 Cu<0.10, Zn<0.10, Be< 0.03, balanced aluminium and impurities. This aluminium die-casting alloy does not suffer from die-sticking and cast products are capable of achieving yield strength of at least 1 17 MPa and an elongation of at least 18%.

US-A-4605448 disclosed an aluminium wrought alloy for use in manufacturing both can body parts and can ends, the aluminium wrought alloy having a composition, in weight percent: Mg 0.50 - 1 .25, Mn 0.30 - 1 .50, Si 0.52 - 1 .00, balanced aluminium and impurities.

From these disclosed arts, the existing researches in the field of high-strength and improved mechanical performance casting aluminium alloys have the following problems: the strength of the aluminium alloy is not high enough, more particularly, lack of casting aluminium alloys has the yield strength higher than 300MPa;

precious metals and rare elements (Ag, Sc, Rare earth elements) are added at a higher level, and high-purity aluminium is used as the base metals, thus increasing the cost, limiting the material source and making the aluminium alloy difficult to be popularized and put into civil use, and the contradiction between the strength and castability of the alloy is serious. More particularly, the existing arts are not within the technical field of the casting aluminium alloys that are based on Al-Mg-Zn-Si system and can provide a UTS over 420MPa and a yield strength over 300MPa with an elongation over 6%.

Other references which disclose aluminium alloys include DE 1272553 B; CN 101445879 A; GB 2090289 A; US 2002/0006352 A1 ; US 2290022 A; and US 2290019 A.

The present invention seeks to provide an improved high strength casting aluminium alloy material with excellent castability and low formula cost and therefore easy for massive production. Preferably a casting aluminium alloy is provided for making products having the mechanical properties of the minimum mechanical properties of a 0.2% yield strength of 300MPa, a tensile strength (UTS) of 420MPa and an elongation at fracture of at least 6%.

This invention seeks to provide a casting aluminium alloy that can be used in a variety of casting operations, in particular including but not being limited to sand casting, investment casting, lost foam casting, gravity permanent mould casting, low pressure die casting, high pressure die casting and squeeze casting operations.

This invention also seeks to provide improved cast products and components manufactured from the casting aluminium alloy cast members that are ideally suited for transportation applications.

In a first aspect of the invention, there is provided an aluminium alloy including, relative to the total weight of the aluminium alloy, including the following

components: greater than 6.0 (preferably greater than 7.0) and up to 15.0 wt-% of magnesium, greater than 1 .8 and up to 7.0 wt-% of zinc, greater than 1 .5 and up to 5.0 wt-% of silicon, from 0.05 to 2.0 wt-% of manganese, and additionally at least one element from 0 to 0.5 wt-% beryllium, 0 to 2.5 wt-% calcium, 0 to 1 .5 wt- % strontium, 0 to 1 .0 wt-% titanium, 0 to 1 .5 wt-% copper, 0 to 0.5 wt-% boron, 0 to 1 .0wt-% scandium and 0 to 2.0 wt-% rare earth elements, and the reminder of the alloy is aluminium and inevitable impurities.

The casting aluminium alloy according to the present invention is preferably capable of achieving the mechanical properties of 0.2% yield strength of 300MPa, a tensile strength (UTS) of 420MPa and an elongation at fracture of 6%. The mechanical properties can be varied and adjusted according different

requirements. For example, the yield strength can be as high as 450MPa if the elongation is at a very low level. The elongation can be up to 10% if the yield strength is required to be less than 200MPa.

A realisation of the present invention is that Zn can be employed in casting Al-Mg- Si alloys to provide a strengthening effect after heat treatment. Previously, Zn is generally recognised as an impurity in Al-Mg-Si alloys and is limited at a low level in order to reduce casting defects. However, the casting performance of Al-Mg-Si alloys can be significantly improved when Si level is greater than 2wt%.

Therefore, in the specific composition of casting Al-Mg-Si alloys, the addition of Zn will not cause casting problems. The formation of Zn-rich intermetallics in the as- cast microstructure can be dissolved into the aluminium matrix and precipitated during heat treatment to provide improved mechanical properties in Al-Mg-Si casting alloys without increase the defects levels. As such, Zn is an effective strengthening element in casting AI-Mg-SI alloys.

In a second aspect, the present invention provides products made from the casting Al-Mg-Zn-Si based aluminium alloys set out a variety of casting operations, which including the common casting methods including but not limited to sand casting, investment casting, lost foam casting, gravity and permanent mould die casting, low pressure die casting, high pressure die casting, and squeeze casting. The casting aluminium alloy is particularly suited for manufacturing products having load and impact requirements where properties of high strength are desirable.

In an alternative aspect of the invention, there is provided an aluminium alloy including, relative to the total weight of the aluminium alloy, 6.0 to 15.0 wt-% of magnesium, 0.6 to 7.0 wt-% of zinc, 1 .0 to 5.0 wt-% of silicon, 0.05 to 2.0 wt-% of manganese, and additional at least one element from 0 to 0.5 wt-% beryllium, 0 to 2.5 wt-% calcium, 0 to 1 .5 wt-% strontium, 0 to 1 .0 wt-% titanium, 0 to 1 .5 wt-% copper, 0 to 0.5 wt-% boron, 0 to 1 .0wt-% scandium and 0 to 2.0 wt-% rare earth elements, and the balancing amount of aluminium and inevitable impurities.

In a further alternative aspect of the invention, there is provided an aluminium alloy including, relative to the total weight of the aluminium alloy, greater than 6.0 and up to 15.0 wt-% of magnesium, greater than 0.6 to 7.0 wt-% of zinc, greater than 2.0 to 5.0 wt-% of silicon, 0.05 to 2.0 wt-% of manganese, and additional at least one element from 0 to 0.5 wt-% beryllium, 0 to 2.5 wt-% calcium, 0 to 1 .5 wt-% strontium, 0 to 1 .0 wt-% titanium, 0 to 1 .5 wt-% copper, 0 to 0.5 wt-% boron, 0 to 1 .0wt-% scandium and 0 to 2.0 wt-% rare earth elements, and the balancing amount of aluminium and inevitable impurities. By the present invention the casting products can be provided not only having high strength in combination with acceptable elongation at fracture, but also having good castability. Therefore it is suitable for common castings methods, in particular in die-casting operations without soldering problems. It is found that the improved mechanical properties available with the present invention, particularly improved strength levels in combination with good casting characteristics result from the combined additions of Mg, Zn and Si in aluminium within the given ranges. The casting aluminium alloy is not only applicable under as-cast condition, but also ideally suitable for strengthening with solution and ageing heat treatment, in which the high temperature solution heat treatment can be significantly shortened in comparison to the conventional ones; and the ageing at elevated temperature provides the complexly shaped cast products with improved dimensional stability and mechanical properties.

This invention adopts the Al-Mg-Zn-Si based system. Mg, Zn and Si are added to the alloy to reduce the liquidus temperature and to improve the castability and to increase the solution strengthening and precipitation strengthening. For these reasons the preferred lower limit is set at Mg of 7.0%, Zn of 1 .8% and Si of 1 .5%. Further additions of Mg and Si help to improve the castability, but will produce primary Mg₂Si phase in the as-cast microstructure, which results in the reduction of the strength. Therefore, the preferred upper limit is set to 15.0%Mg and 5.0%Si. The control of Mg content in the alloy is in such a way that the higher Mg content is against to a lower Si content. The main role of Zn is to provide strengthening phase in the as-cast condition and in the heat-treated condition. Therefore, the higher Zn content provides the alloy with increased strength, but with reduced elongation. Therefore, the preferred upper limit is set 7.0% for Zn.

Copper can be used as a replacement for Zn to provide a strengthening effect and therefore Cu substantially improves strength in the as-cast and heat-treated conditions. However, Cu usually reduces resistance to general corrosion and, in specific compositions and material conditions, stress corrosion susceptibility. Addition of copper also reduces hot tear resistance and thus decreases castability. For these reasons the Cu content needs to be tightly controlled. The upper limit of Cu is preferably set at 1 .5%, but most preferably is less than 0.3%. Rare earth elements can be used as alternatives for Zn and Cu, but their content should be controlled at low levels due to high cost. The upper limit of Re is preferably set to be 2.0%, but the most preferred level is less than 0.8%. In the present invention, the Zn can provide the strengthening results obtained by other elements after carefully optimisation.

Mn is an important alloying element for all embodiments of the casting aluminium alloy according to the present invention. The role of Mn includes the neutralisation of Fe to form compact Fe-rich intermetallics which are less detrimental that needle-shaped Fe-rich intermetallics, and to promote die releasing during die casting which allow the alloy to be die castable for massive production. For these reasons, Mn content is lower in the castings made by sand casting and other method without using a metallic mould, but higher in the casting methods using metallic mould. The Mn level should preferably be in the range of 0.1 to 2.0%. A more preferred Mn level is in the range of 0.1 to 1 .0%, and the most preferred level is in the range of 0.2-0.6%.

Fe is a well-known detrimental element in casting aluminium alloys and may be present in a range of up to (preferably) 2.0 %. At higher levels Fe may form undesirable large compounds with Mn in the casting. When ductility is required at a reasonable level, Fe content needs to be preferably controlled below 0.5 %, and most preferably 0.1 %.

Ti is important as a grain refiner during solidification of both cast products using the alloy of the present invention. A preferred maximum for Ti addition is 0.2 %, and a more preferred range is of 0.01 to 0.15 %. Be is added to magnesium containing casting alloys to prevent oxidation of the magnesium in the aluminium alloy, the amount added into the alloy varies with the magnesium content. As little as up to 0.001 % causes a protective beryllium oxide film to form on the surface. Preferably, the Be level has a level of 0.15%, and most preferably is absent without detonating the properties of the cast product with this invention, but a level of 0.002%Be is found to be really helpful for the melt processing. Ca can used as an alternative for Be to protect the alloy from oxidation. The Ca content can be controlled up to (preferably) 2.5%, but most preferably, Ca is needed to be controlled below 1 .0%.

By adding slight amounts of rare earth elements the casting defects of the aluminium alloy casting can be reduced. The increased uniformity of structure and increased fineness of dispersion are achievable. Therefore, the strength of the aluminium alloy casting can be strikingly improved. Furthermore, the presence of rare earth elements contributes to make the grain size of the casting finer

(improving its strength and ductility), and modifies the eutectic structure of the alloy according the present invention. Therefore, the Re level can be up to

(preferably) 2.0%, but the most preferred level is less than 0.8%. The balance is aluminium and inevitable impurities. Typically each impurity is present at 0.05 % maximum and the total of impurities is 0.25 % maximum.

In a preferred embodiment of the casting aluminium alloy according to the present invention of the preferred levels of the alloying element are selected: Mg greater than 7 and up to 12%, Zn greater than 1.8 and up to 5%, Si greater than 1 .5 and up to 3.5%, MnO.1 -1 .0%, and additionally at least one element from Be 0-0.15%, Sr 0-0.15%, Ti 0 -0.4%, B 0- 0.2% with balance aluminium and inevitable impurities.

In another preferred embodiment of the casting aluminium alloy according to the present invention of the preferred levels of the alloying element are selected: Mg 8 - 10%, Zn 2 - 4%, SM .5-3%, MnO.2-0.8%, and additionally at least one element from Be 0-0.05%, Sr 0-0.08%, Ti 0 -0.15%, B 0- 0.1 % with balance aluminium and inevitable impurities.

In a particularly preferred embodiment, Mg is present at 8 to 1 1 wt-%, and Si is present at 2.4 to 2.8 wt-%.

In these embodiments high strength are achieved due to the high Mg, Si and Zn levels and the improved castability is achieved by the Si level. As a result of this high Mg, Si and Zn levels, the solution and ageing strengthening are capable of providing the increased strength with required elongation.

To improve the mechanical properties of the alloy, different heat treatment can be used. T6 heat treatment is which gives best results. Anyhow, another heat treatment known in the art (such as T4, T5 heat treatments) may also be suitable. T6 heat treatment comprises 2 steps: homogenizing and quenching-age

hardening. During homogenizing step, what is done is to support the rough casting part to high temperature, in the range from about 400 to 600 °C, during a period of time that can be of the order of 10 minutes to over 10 hours. Preferably the temperature is about 460 °C and the time 2 hours. Once the microstructure is homogenized, the part is quenched, i.e. is suddenly cooled. The step from the homogenizing furnace to the quenching must be carried out in as short a period of time as possible, since otherwise it would begin the selective precipitation.

According to a preferred embodiment, this time is less than 15 seconds. Next, the quenched parts are introduced again in another treatment furnace, wherein it is in the age-hardening step. This age-hardening step is carried out at low temperature, preferably in the range of about 150 to 220 °C. The age-hardening step gives the mechanical and technological properties to the casting part.

The casting aluminium alloy in accordance with the present invention can be processed by applying various casting techniques including but not being limited to sand casting, investment casting, lost foam casting, gravity permanent mould casting, low pressure casting, high pressure die casting and squeeze casting. The best results are achieved when applied via low pressure de casting, or vacuum assisted high pressure die casting, or squeeze casting. The best combination of desirable properties and castability characteristics are obtained in associated with the slight change of alloy composition and process.

A number of preferred embodiments of the invention will now be described, with reference to the following non-limiting examples.

Example 1

The alloy was made for sand casting with international standard tensile test samples. The test sample is machined from castings under as-cast condition and under heat-treated condition. The heat treatment including solution treatment (T4) and solution with subsequent ageing heat treatment (T6). The composition of tested alloys and the related mechanical properties are given in following Table.

for 120min)

From the results in the Table it can be seen that the aluminium alloy according to the present invention results in very high tensile properties and elongation in the heat treated condition, although the mechanical properties under as-cast condition has been already attractive in comparison with the currently available alloys. These surprisingly high properties are achieved with the need for further heat treatments. The heat treatment is shorter in comparison with the commonly used techniques.

Example 2

The 6.35mm vacuum die-cast products are made using high pressure die casting with conventional used vacuum assisted system. The degree of vacuum is controlled at 0.6atm in the die cavity. The die cast samples are tested under as- cast condition and under heat-treated condition. The heat treatment including solution treatment (T4) and solution with subsequent ageing heat treatment (T6). The composition of tested alloys and the related mechanical properties are given in following Table.

for 90m in)

The castings made by high pressure die casting process are usually not able to be solution treated because of the occurrence of blisters on the casting surface. The vacuum assisted high pressure die casting is beneficial for the subsequent heat treatment because of the less gas porosity in the casting. It needs to emphases that the conventional high pressure die castings are still possible to make castings for subsequent solution heat treatment when the parameters are optimised and the porosity inside the casting is under a controlled level.

Example 3

Gravity casting with a diameter of 10mm in the middle of standard tensile samples are made by high strength alloy. The casting samples are tested under as-cast condition and under heat-treated condition. The heat treatment including solution treatment (T4) and solution with subsequent ageing heat treatment (T6). The composition of tested alloys and the related mechanical properties are given in following Table.

Alloy Heat treatment 0.2% yield Ultimate Elongation composition condition strength tensile at fracture

for 90m in)

All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.

The disclosures in UK patent application number 1415420.7, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Claims

1 . A casting Al-Mg-Zn-Si based aluminium alloy material for providing improved mechanical performance, including the following components:

greater than 7.0 and up to 15.0 wt-% of magnesium,

greater than 1 .8 and up to 7.0 wt-% of zinc,

greater than 1 .5 and up to 5.0 wt-% of silicon,

from 0.05 to 2.0 wt-% of manganese,

and additionally at least one element from 0 to 0.5 wt-% beryllium, 0 to 2.5 wt-% calcium, 0 to 1 .5 wt-% strontium, 0 to 1 .0 wt-% titanium, 0 to 1 .5 wt-% copper, 0 to 0.5 wt-% boron, 0 to 1.0wt-% scandium and 0 to 2.0 wt-% rare earth elements, and the reminder of the alloy is aluminium and inevitable impurities.

2. An alloy as claimed in claim 1 , including the following components by weight percentage:

greater than 7.0% and up to 12.0% of magnesium,

greater than 1 .8% to 5.0% of zinc,

greater than 1 .5% and up to 3.5% of silicon,

from 0.1 % to 1 .0% of manganese,

and additionally at least one element from 0 to 0.15 wt-% beryllium, 0 to 1 .0 wt-% calcium, 0 to 1 .5 wt-% strontium, 0 to 0.5 wt-% titanium, 0 to 0.8 wt-% copper, 0 to 0.2 wt-% boron, 0 to 0.3wt-% scandium and 0 to 1 .0 wt-% rare earth elements, and the remainder of the alloy is aluminium and inevitable impurities.

3. An alloy as claimed in claim 1 or 2, including the following components by weight percentage:

from 8.0% to 10.0% of magnesium,

from 2.0% to 4% of zinc,

greater than 1 .5% and up to 3.0% of silicon,

0.2% to 0.8% of manganese, and additionally at least one element from 0 to 0.05 wt-% beryllium, 0 to 1 .0 wt-% calcium, 0 to 0.08 wt-% strontium, 0 to 0.15 wt-% titanium, 0 to 0.3 wt-% copper, 0 to 0.1 wt-% boron, 0 to 0.2wt-% scandium and 0 to 0.8 wt-% rare earth elements, and the remainder of the alloy is aluminium and inevitable impurities.

4. An alloy as claimed in any one of claims 1 to 3, wherein the magnesium and silicon contents are selected to form hypoeutectic but near eutectic microstructures in the developed alloy.

5. An alloy as claimed in any one of claims 1 to 4, wherein the zinc is partially replaced by copper, scandium or rare earth elements, such that the formed intermetallics are capable of dissolving into matrix under evaluated temperatures.

6. An alloy material as claimed in any one of claims 1 to 5, wherein the Fe level is controlled to be less than 2.0wt-%, and preferably less than 0.5wt.% and even more preferably less than 0.1 %.

7. An alloy as claimed in any one of claims 1 to 6, wherein the aluminium alloy is workable under as-cast condition and under heat treated condition.

8. An alloy as claimed in any one of claims 1 to 7, wherein the aluminium alloy is capable of providing an ultimate tensile strength (UTS) of 420 MPa, and 0.2% yield strength of 300 MPa, and an elongation at fracture of 6 %, which can be easily varied according to different requirements.

9. A casting process employing an alloy as claimed in any one of claims 1 to 8.

10. A casting process as claimed in claim 9, which is sand casting, investment casting, lost foam casting, gravity permanent mould casting, low pressure die casting, high pressure die casting or squeeze casting operations.

11. A product obtainable from a casting process as claimed in any of claims 9 or 10.