WO2015173237A1

WO2015173237A1 - An alloy

Info

Publication number: WO2015173237A1
Application number: PCT/EP2015/060467
Authority: WO
Inventors: Emeka IKWUEZE; Pete BLACKMORE; Ashley BROUGH; Simon RUFFLE; Wayne MURCOTT
Original assignee: Jaguar Land Rover Limited
Priority date: 2014-05-12
Filing date: 2015-05-12
Publication date: 2015-11-19
Also published as: EP3143174A1; GB201408299D0; GB2526085A

Abstract

An aluminium silicon alloy suitable for use in automotive or aerospace die castings is described. The alloy comprises at least 8 wt% and at most 12 wt% silicon; up to around 0.30 wt% iron; and manganese, wherein the composition comprises manganese in an amount that is greater than the amount of iron present in the composition; and wherein the balance of the composition comprises aluminium. Methods of making the alloy and for making die castings are provided.

Description

AN ALLOY

FIELD OF THE INVENTION

The invention relates to aluminium-silicon alloys for use in die casting of structural components. The invention further relates to methods of making and using such alloys.

BACKGROUND OF THE INVENTION

Aluminium alloys are used in the production of high pressure die castings for structural body parts used in the manufacture of motor vehicles and other heavy machinery. Aluminium is favoured for the production of such components due to its ease of handling, its low cost, ease of machinability and because it is relatively lightweight. Die castings typically comprise complex geometry including parts that may require welding or riveting to other structural components. As a result, structural die castings will be subjected to considerable loads when in use, particularly if they contribute to the chassis, powertrain, subframe or suspension system of a motor vehicle.

To meet the stringent requirements of strength, ductility and resistance to metal fatigue whilst retaining good castability, aluminium-silicon eutectic system alloys (silumin) are 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. It is preferred, therefore, that the iron content in aluminium-silicon alloys is maintained at a level that is below 0.15 wt%, and preferably even lower. Consequently, such requirements discourage the use of recycled materials as a source of aluminium for die castings, so-called secondary alloys, because the levels of contaminating iron are simply too high. Hence, there is dependence in the art upon more costly primary alloys that are manufactured from pure aluminium that is alloyed with silicon and other additive elements to improve its mechanical properties It would be a considerable advantage if novel casting secondary alloys could be formulated that allow for an increased use of recycled materials in order to reduce C0₂ emissions as well as the overall cost of manufacturing die cast objects, without compromising the important material and mechanical characteristics of the alloy.

The present invention provides alloy compositions that meet the aforementioned objectives. 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

The present invention relates to alternative compositions and processes for manufacturing an aluminium alloy that exhibits satisfactory mechanical and material properties such that it can be used in die castings for automotive and aerospace

applications.

A first aspect of the invention provides an aluminium-silicon alloy composition comprising:

- at least 8 wt% and at most 12 wt% silicon;

- up to around 0.30 wt% iron; and

- manganese, wherein the amount of manganese present in the composition is greater than the amount of iron; wherein the balance of the composition comprises aluminium.

In a specific embodiment of the invention the aluminium is derived from secondary sources, and therefore comprises a substantial proportion of recycled aluminium-containing material.

Suitably the aluminium-silicon alloy of the invention comprises at least 8.5 wt% silicon, optionally about 9 wt% silicon, more optionally around 10 wt % silicon. Typically the aluminium-silicon alloy of the invention will comprise less than 1 1 wt % silicon and optionally no more than 10.5 wt% silicon.

According to certain embodiments of the invention the aluminium-silicon alloy may comprise at least 0.01 wt% iron, however typically it is expected that the baseline iron content is likely to be in the region of at least 0.10 wt% and more typically at least 0.15 wt%. In specific embodiments of the invention the aluminium-silicon alloy comprises not less than 0.16 wt% iron. The aluminium-silicon alloy of the invention further comprises manganese in an amount defined by a ratio that is dependent upon the iron content of the aluminium source. Hence the amount of manganese may vary from composition to composition but is within boundaries set by the invention. As stated, according to the invention the amount of manganese is always greater than the amount of iron and in specific embodiments of the invention the ratio of iron to manganese is at least about 0.2 and at most about 0.8. In specific embodiments of the invention the iron to manganese ratio is at least 0.3, suitably at least 0.4, optionally 0.5 and up to around 0.75.

In a specific embodiment of the invention, the iron to manganese ratio is set at a level to ensure that majority of iron-containing intermetallic phase particles assume a polyhedral morphology within the microstructure of the alloy.

In specific embodiments of the invention the aluminium-silicon alloy comprises less than 0.1 wt% of magnesium and/or is substantially free of elements such as: molybdenum and zirconium. According to one embodiment of the invention the composition is heat treated (i.e. annealed). Suitably heat treatment occurs at a temperature of at least around 350 ^<€, optionally at least around 360 °C, suitably up to around 390 °C. In a particular embodiment of the invention heat treatment occurs at a temperature of up to at most around 385 °C.

A second aspect of the invention provides for a method of manufacturing an aluminium-silicon alloy composition that is suitable for use in automotive and aeronautical castings. The method comprises adding to a source of aluminium that comprises at least 0.16 wt% iron, the following elements selected from:

(a) silicon, wherein the silicon is added at an amount of at least 8 wt% and at most 12 wt% of the total alloy mixture; and

(b) manganese, wherein the amount of manganese is determined by an iron to

manganese ratio of at least about 0.2 and at most about 0.8.

In a specific embodiment of the invention the method comprises the additional step of forming the alloy into a die casting and heat treating the die casting.

A third aspect of the invention provides for a die casting manufactured from the alloys of the present invention. Suitably the casting is for use in the automotive industry. In particular embodiments of the invention the die casting may constitute a part or component that is comprised within the body, chassis, powertrain, sub-frame or suspension system of a motor vehicle. A fourth aspect of the invention provides for a method of die casting a component comprising, forming a die mould that defines the configuration of the component, injecting the molten aluminium-silicon alloy of the invention into the die mould and allowing the alloy to cool to form a solid die cast component. In embodiments of the invention the component may be subjected to additional heat treatment as described herein.

A fifth aspect of the invention provides a motor vehicle that comprises a part that includes or is comprised of a part or component manufactured from an aluminium-silicon alloy of the invention.

A sixth aspect of the invention provides for a use of an aluminium-silicon alloy comprising an iron content of at least 0.16 wt% for manufacturing a die casting for a body in white (BiW) component of a motor vehicle. In specific embodiments of the invention the aluminium-silicon alloy comprises at least 0.16 wt% iron and at most around 0.30 wt %. In one embodiment of the invention the aluminium-silicon alloy comprises at least 0.30 wt% iron. In particular, embodiments of the invention the use of the alloy contributes to a casting may be a part or component that is comprised within the body, chassis, powertrain, sub- frame or suspension system of a motor vehicle. According to one embodiment of the invention the die castings are suitable for use as components of Body in White (BiW) body panels and sub-assemblies.

A seventh aspect of the invention provides an aluminium-silicon alloy composition, for use in die casting, comprising at least 8 wt% and at most 1 1 wt % silicon, optionally no more than 10.5 wt% silicon, up to around 0.30 wt% iron, and manganese, wherein the amount of manganese present in the composition is greater than the amount of iron, wherein the balance of the composition comprises aluminium. Embodiments in accordance with the aforementioned aspect are particularly useful for use in high pressure die casting of automotive components and, in a particular, structural components e.g. engine mount brackets.

In one embodiment in accordance with the aforementioned aspect, the composition is heat treated (i.e. annealed). A post casting heat treatment is particularly beneficial for the manufacture of Body in White (BiW) structural components, which may include, for example, shock absorber towers. Suitably heat treatment occurs at a temperature of at least around 350 °C, optionally at least around 360 °C, suitably up to around 390 °C. In a particular embodiment of the invention heat treatment occurs at a temperature of up to at most around 385 °C. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a micrograph showing a section through a conventional Al-Si alloy that comprises iron inclusions, intermetallic phase particles, as impurities. An iron inclusion that has adopted a 'script' configuration is marked as (A), whereas (B) denotes a particle that has adopted a more regular polyhedral shape.

Figure 2 micrographs of showing sections through three Al-Si alloys of embodiments of the invention having increasing levels of iron content, the three alloys are denoted as Low Fe (0.16 wt%), Medium Fe (0.31 wt%), and High Fe (0.55 wt%). A comparative conventional low iron content Al-Si alloy is also shown (denoted Comp).

Figure 3 shows an analysis of variation box plot of a proof stress test for Al-Si parts treated at the three different annealing temperatures (350 °C, 365 °C and 385 °C) as well as for a non-heat treated control (denoted AC for "as cast").

Figure 4 shows an analysis of variation box plot of an elongation test for Al-Si parts treated at the three different annealing temperatures (350 °C, 365 °C and 385 °C) as well as for a non-heat treated control (denoted AC for "as cast").

Figure 5 shows a scatter plot of the data from Figures 3 and 4 for the AC (diamond shaped points) and 385C alloys (square points) overlaid against results obtained for control parts manufactured from a conventional primary aluminium Al-Si alloy (Comparison) which is heat treated.

Figure 6 is a graph showing the results of a Coupon Test in which strain-life versus fatigue damage values for the control alloy (Comparison) are overlaid with results obtained from 385 °C heat treated Al-Si alloy of an embodiment of the invention (denoted "HT combined") and non-heat treated alloy embodiment (denoted "as cast").

Figure 7 is a graph of Coupon Testing showing the results of cyclic strain versus cyclic stress in Al-Si alloys of the embodiments of the invention shown in Figure 6.

Figure 8 is a graph of the results of a tensile strength test on multiple samples of parts manufactured from control alloy (Comparison), 385 °C heat treated alloy of an embodiment of the invention (denoted Rivalloy HT) and non-heat treated alloy of an embodiment of the invention (denoted Rivalloy AC).

DETAILED DESCRIPTION OF THE INVENTION All references cited herein are incorporated by reference in their entirety. 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.

Prior to setting forth the invention, a number of definitions are provided that will assist in the understanding of the invention.

The term "alloy" is used herein to denote a metallic substance comprising a mixture of a predominating metallic element and other elements, including impurities. The basic aluminium-silicon (Al-Si) alloy forms a simple eutectic system at around 12 weight% (wt%) silicon being the eutectic composition at 577 °C. Al-Si alloys are usually referred to as near- eutectic alloys when silicon content is around about 10% and up to about 13% of the total weight of the alloys. Eutectic (or near-eutectic) Al-Si alloys are used extensively in die casting applications particularly in the automotive and aerospace industries. Suitably, most Al-Si alloys used in casting may contain 50-90 vol% eutectic. Conventional Al-Si alloys suitable for use in die casting applications typically meet industry standards such as European Standard EN 1676 which defines the requirements for various grades of alloyed aluminium ingots intended for remelting. It is believed that the alloys of the present invention show high levels of equivalence in terms of suitability for use in die casting, especially for automotive and aerospace parts.

"Die casting" is a manufacturing process that can produce metal components through the use of reusable molds, called dies. The die casting process involves a furnace, metal, die casting machine, and die. The metal, typically a non-ferrous alloy comprising aluminium, is first melted in the furnace and then injected, optionally under pressure, into the dies in the die casting machine. Once the casting has cooled and has set the part can be subjected to additional tooling or trimmed and finished. Die 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. The process supports a reasonably high rate of production and is favoured producing consistent parts with good surface finish.

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 die 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 and aircraft.

As used herein the term "impurity" refers to a metallic or non-metallic element that is present in an alloy but which is not added intentionally. Hence, no lower limit is specified for the presence of the impurity. In Al-Si alloys a significant impurity is iron (Fe) which forms intermetallic phase particles, or crystalline "inclusions", within the microstructure of the alloy. Iron is a common impurity in aluminium alloys that arises from a number of possible sources and which, at least for Al-Si based casting alloys, is usually considered detrimental for several reasons. There is no economical way to remove iron from aluminium so primary low values of between 0.10 and 0.15 wt% are the typical baseline levels found in primary pure aluminium and all further melt activities only serve to potentially increase the iron level further.

Iron tends to combine with other elements present in eutectic Al-Si alloys to form the aforementioned intermetallic phase particles. Typical iron containing inclusions in Al-Si alloys include AI₈Fe₂Si and, when manganese is present, AI₁₅(Fe, Mn)₃Si₂. Both of these materials are able to assume particulate morphology that is script-like, although when manganese is present a polyhedral crystalline form may also be obtained (see Figure 1 ). The quantity and density of the intermetallic inclusions increases with increasing iron concentration in the alloy and this is known to result in a reduction in ductility and yield strength of the alloy as a whole. Intermetallic phase particles that adopt the script morphology are the most detrimental to the properties of the alloy contributing to the fracture mechanism and also bringing about an increase in porosity.

The microstructure of a solid alloy takes form when a metal cools from molten liquid phase to a solid metal. This solidification forms a polycrystalline metal with different orientations of the grains. These grains will form the microstructure of the alloy and will contribute to its material properties including strength, resistance to fatigue and ductility. The form of this microstructure depends not only upon the heat transfer but also upon the alloy composition. The two major growth types of microstructures include the dendritic and the eutectic. Both types of growth are present in almost every aluminium alloy casting because of the improved castability of a near-eutectic or eutectic alloy than that of other compositions. Al-Si alloys typically used in die casting applications will usually comprise a two-phase microstructure. This means that the alloy comprises larger grains (known as dendrites) that are predominantly comprised of aluminium with a small silicon component. During cooling, at the point that the eutectic temperature is reached the eutectic phase will begin to solidify between the dendrite arms filling this volume out. The eutectic phase consists of a primary a- aluminium phase and a silicon phase. This will give a two-phase microstructure where the primary a-aluminium crystals (dendrites) are distributed within the Al-Si eutectic phase. The ratio between the two phases will depend on the content of silicon and also the solidification time. Figure 1 shows a typical two-phase microstructure of a conventional Al-Si alloy. According to the present invention there is provided an Al-Si alloy composition that is suitable for use in manufacture of die casting parts that tolerates an impurity content that is substantially elevated compared to that hitherto considered viable. In specific embodiments of the present invention it is found that an iron content of up to around 0.30 wt% of the alloy can be tolerated without a substantial effect upon the mechanical strength or ductility of the alloy that would compromise its ability to be used in die casting. In addition, the present alloys do not require the presence of costly grain refining elements such as molybdenum or zirconium. This means that the alloys of the present invention may be manufactured using secondary sources of aluminium (including recycled material) that results in a significant reduction in cost and carbon footprint. The ability to utilise recycled starting materials also enables the alloy to be produced from local sources of aluminium. The effect of this is to reduce the considerable distances needed to transport high grade primary aluminium alloy from the foundry to the manufacturing site. This results in a significant reduction in the carbon footprint for the alloys of the present invention. Further, the energy savings made in recycling aluminium are considerable. Remelting requires only about 5 % of the energy initially required to produce primary aluminium. In an embodiment of the invention, it is estimated that the current process reduces the amount of C0₂ emitted by over 9 tonnes per tonne of metal alloy produced when compared to conventional primary Al-Si alloys.

In a specific embodiment of the invention an alloy is provided as set out in Table 1 , with the balance made up from aluminium:

Table 1

It is envisaged that alloys of the invention may suitably comprise anything up to about

13 wt% of silicon, optionally at most 1 1 wt%. Typically the minimum content of silicon in the alloy will be at least 7 wt%, more suitably at least around 8 wt %, optionally at least about 9 wt%.

The alloys of the invention do not require the presence of additional grain refining elements such as zirconium and molybdenum, or iron neutralising elements such as beryllium, cobalt and chromium. Hence, the alloys of the invention provide a saving in terms of cost and ease of manufacture. A specific embodiment of the invention provides for an Al-Si alloy in which the iron to manganese ratio is maintained at a level of at least 0.20 and optionally up to around 0.80. This is considerably higher than previously known, where iron is usually the more abundant component with ratio maintained at around 2.0 in order to prevent the formation of hard spots in the die casting which can hinder subsequent machining of the parts. By maintaining a higher manganese to iron content, according to the present invention, iron impurity levels can be tolerated that are double those typically found in Al-Si alloys made from primary sources of aluminium. The present inventors have not observed any reduction in the handling or working-ability of parts and components manufactured from the novel Al-Si alloys.

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

EXAMPLES

Example 1 - Qualitative analysis of alloys comprising increasing iron content

Three Al-Si alloys were prepared with increasing levels of iron (Fe) as an impurity. The three alloys were denoted as Low Fe (0.16wt%), Medium Fe (0.31wt%), and High Fe (0.55wt%). The manganese content was adjusted to maintain a greater proportion of manganese to iron.

Qualitative analysis was performed on sections of alloy (see micrographs set out in

Figure 2) to determine the number and size distribution of intermetallic phase particles of (FeMn)₃Si₂Ali₅. The sizes of these particles fell into two main bands: large (15-24μιη in diameter) and small (approximately 3μιη in diameter). The large particles had most probably nucleated in the liquid alloy prior to casting which had allowed agglomerations to form. The small particles, conversely, had precipitated during investment of the castings and, thus, had little time to grow or agglomerate. A comparison was made against a conventional die- casting Al-Si alloy made from low iron content primary aluminium (Comparison). It should be noted that the comparison is a hypo-eutectic AISi₉Mn alloy of the type typically used to manufacture high pressure die cast (HPDC) components that possess enhanced ductility compared with conventional HPDC alloy grades such as EN 1706:2010 AC- AISi₉Cu₃Mg(Fe)(Zn). The data in Table 2 shows that whilst the absolute number of intermetallic phase particles may increase slightly as iron content increases the size of the particles increases preferentially as particles having a polyhedral rather than a script morphology. This is a surprising result and contributes to the unexpectedly good strength and ductility performance of the high iron Al-Si alloys of the invention. According to conventional understanding, there would be an expected increase in particles having script morphology, however, this is not seen.

Table 2

Example 2 - Effects of heat treatment on parts made from Al-Si alloys of the invention

An Al-Si alloy of the invention having a composition substantially as set out in Table 1 was used to form die casting parts. The parts were subjected to annealing temperatures of 350 °C, 365 °C and 385 °C for a period of 25 minutes before being tested for mechanical properties. Figure 3 shows an analysis of variation box plot displaying the results of a yield test with results presented as box plot of 0.2% proof stress for parts treated at the three different annealing temperatures as well as for a non-heat treated control (denoted AC). The yield test provides an estimation of the performance of the alloy under load and particularly the minimum stress required to cause a 0.2% permanent plastic deformation of the die casting part.

Figure 4 shows an analysis of variation box plot of the results of a tensile test according to ASTM E8M-09 in which measurements are made of the extension of the test part under increasing load. The results of the tests presented in Figures 3 and 4 show that whilst mechanical strength reduces somewhat upon heat treatment the ductility increases. Hence there is a trade-off between strength and ductility that allows for the skilled person to tailor the needs of a specific alloy for different requirements when in use by exposing the alloy to a range of annealing temperatures. This advantageously allows for the alloys of the invention to be used for Body in White (BiW) applications - in spite of the high iron intermetallics content - where high ductility of castings is necessary.

The die cast parts manufactured from Al-Si alloys of the invention whether heat treated or not have mechanical properties that are highly comparable to known Al-Si alloys that are manufactured from primary sources of aluminium and which comprise low levels of iron impurities. Figure 5 shows a scatterplot of elongation versus yield (0.2% proof stress) in which values for the control alloy (Comparison) are overlaid with results obtained from 385 °C heat treated alloy of the invention (denoted Rivalloy annealed) and non-heat treated alloy of the invention (denoted Rivalloy as cast). It is apparent from Figure 5 that the mechanical performance of both the annealed and non-heat treated die cast alloys of the invention are highly comparable to that of the control. This is highly surprising as it would be expected that the considerably higher iron content (around two-fold increase in iron) would have quite profoundly negative effects on ductility and strength. Hence, from a metallurgical perspective it can be concluded that the present Al-Si alloys are highly equivalent in terms of their die-casting properties when compared to the more expensive and less environmentally friendly Al-Si alloys previously known.

Example 3 - Fatigue tests on parts made from Al-Si alloys of the invention

The die cast parts manufactured from Al-Si alloys of the invention whether heat treated or not have comparable metal fatigue profiles to known Al-Si alloys that are manufactured from primary sources of aluminium and which comprise far lower levels of iron impurities. Figure 6 shows the results of a conventional Coupon Test. This procedure describes a method for performing strain-controlled, axial fatigue testing on specimens with the aim of producing the data necessary for the generation of the characteristic strain-life fatigue properties of metallic materials. The testing method, based upon guidance contained within standards BS 7270, ASTM E 606 and ISO 12106, and is restricted to uniaxially loaded, parallel section samples tested at ambient temperature in laboratory air. The specimens were tested on an MTS 810™ servo-hydraulic test machine (MTS Systems Corporation, Eden Prairie, MN, USA) at room temperature with strain ratio R=-1 . An 8 mm gauge length extensometer was used. The calibration procedure of the test equipment is fully in line with BS EN ISO 9513:2002. The frequency used is 1 Hz as maximum, and 10% of load drop was defined as the crack initiation life. The results are presented as strain versus life with 99.9% survival probability in which values for the control alloy (Comparison) are overlaid with results obtained from all heat treated variants of the invention (denoted HT combined). As alloys of the invention are characterised by the finding iron content has no effect on fatigue, all the heat treated versions were assessed as a single population. Non- heat treated alloy of the invention (denoted "as cast"). The performance of the Al-Si alloys of the invention is broadly similar to that of the low iron control, with the heat treated alloy having a near identical response to fatigue in spite of the significantly higher (almost twofold) iron content. Figure 7 shows the results of Coupon Testing showing the results of cyclic strain versus cyclic stress. The results show that the fatigue profile of annealed Al-Si alloy of the invention is highly comparable to that of the heat treated low iron control.

Example 4 - Strength tests on die cast components

The die cast parts manufactured from Al-Si alloys of the invention whether heat treated or not have comparable static strength properties when compared to the known Al-Si alloys that are manufactured from low iron content primary sources of aluminium. Figure 8 shows the results of a tensile strength rig test under constant load. Multiple samples of parts manufactured from control alloy (Comparison), 385 °C heat treated alloy of the invention (denoted Rivalloy HT) and non-heat treated alloy of the invention (denoted Rivalloy AC) were tested. All parts successfully passed the 120 kN target threshold prior to fracture. The performance of the Al-Si alloys of the invention is broadly similar to that of the low iron control (Comparison), with the heat treated alloy (Rivalloy HT) having a near identical response to fatigue in spite of the significantly higher iron content. The present invention extends to the following aspects as detailed in the following numbered paragraphs (clauses):

1 . An aluminium-silicon alloy composition comprising:

- at least 8 wt% and at most 12 wt% silicon;

- up to around 0.30 wt% iron; and

- manganese, wherein the composition comprises manganese in an amount that is greater than the amount of iron present in the composition; wherein the balance of the composition comprises aluminium.

2. The composition of clause 1 , wherein the aluminium comprises a proportion of recycled material. 3. The composition of clauses 1 or 2, wherein the aluminium-silicon alloy comprises at least 8.5 wt% silicon, optionally about 9 wt% silicon, more optionally around 10 wt % silicon.

4. The composition of clause 3, wherein the aluminium-silicon alloy comprises less than 1 1 wt % silicon and optionally no more than 10.5 wt% silicon. 5. The composition of clause 1 , wherein the aluminium-silicon comprises at least 0.16 wt% iron.

6. The composition of clause 5, wherein the aluminium-silicon alloy comprises 0.30 wt% iron.

7. The composition of any previous clause, wherein the amount of manganese in the composition is determined by an iron to manganese ratio of at least about 0.2 and at most about 0.8.

8. The composition of clause 7, wherein the ratio of iron to manganese is at least 0.3, suitably at least 0.4, optionally 0.5, and up to 0.75.

9. The composition of clauses 7 and 8, wherein the iron to manganese ratio is set at a level to ensure that majority of iron-containing intermetallic phase particles assume a polyhedral morphology within the microstructure of the alloy.

10. The composition of any previous clause, wherein the aluminium-silicon alloy comprises less than 0.1 wt% of magnesium and/or is substantially free of elements such as: molybdenum and zirconium. 1 1 . The composition of any previous clause, wherein the composition is heat treated.

12. The composition of clause 1 1 , wherein the heat treatment occurs at a temperature of at least around 350 °C, optionally at least around 360 °C, suitably up to around 390 °C.

13. The composition of clause 12, wherein the heat treatment occurs at a temperature of up to at most around 385 °C. 14. A method of manufacturing an aluminium-silicon alloy composition that is suitable for use in automotive and aeronautical castings, the method comprising adding to a source of aluminium that comprises at least 0.16 wt% iron, the following elements selected from:

(a) silicon, wherein the silicon is added at an amount of at least 8 wt% and at most 12 wt% of the total alloy mixture; and (b) manganese, wherein the amount of manganese is determined by an iron to manganese ratio of at least about 0.2 and at most about 0.8.

15. The method of clause 14, wherein the method comprises the additional step of forming the alloy into a die casting and heat treating the die casting. 16. The method of clause 15, wherein the heat treatment occurs at a temperature of at least around 350 °C, optionally at least around 360 °C, suitably up to around 390 °C.

17. The method of clause 15, wherein the heat treatment occurs at a temperature of up to at most around 385 °C.

18. The method of any of clauses 14 to 17, wherein the ratio of iron to manganese is maintained at least 0.3, suitably at least 0.4, optionally 0.5, and up to 0.75.

19. The method of any of clause 14 to 18, wherein the aluminium comprises at least 0.30 wt% iron.

20. The method of any of clauses 14 to 19, wherein the silicon is added to a final level of at least 8.5 wt% silicon, optionally about 9 wt% silicon, more optionally around 10 wt % silicon.

21 . A die casting manufactured from the aluminium silicon alloy of any of clauses 1 to 13.

22. The die casting of clause 21 wherein the casting constitutes a part or component that is comprised within the body, chassis, powertrain, sub-frame or suspension system of a motor vehicle. 23. A method of die casting a component comprising, forming a die mould that defines the configuration of the component, injecting the molten aluminium-silicon alloy of any of clauses 1 to 13 into the die mould and allowing the alloy to cool to form a solid die cast component.

24. The method of clause 23, wherein the method further comprises the step of heat treating the component.

25. The method of clause 24, wherein the heat treatment occurs at a temperature of at least around 350 °C, optionally at least around 360 °C, suitably up to around 390 °C.

26. A motor vehicle that comprises a part that includes or is comprised of a part or component manufactured from an aluminium-silicon alloy of any of clauses 1 to 13. 27. Use of an aluminium-silicon alloy comprising an iron content of at least 0.16 wt% and a manganese content that is greater than the amount of iron present in the composition, for manufacturing a die cast part for a motor vehicle.

28. The use of clause 27, wherein the aluminium-silicon alloy comprises at least 0.16 wt% at most around 0.30 wt % iron.

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

WHAT IS CLAIMED IS:

1 . An aluminium-silicon alloy composition, for use in die casting, comprising:

- at least 8 wt% and at most 12 wt% silicon;

- up to around 0.30 wt% iron; and

2. The composition of claim 1 , wherein the aluminium comprises a proportion of recycled material.

3. The composition of claims 1 or 2, wherein the aluminium-silicon alloy comprises at least 8.5 wt% silicon, optionally about 9 wt% silicon, more optionally around 10 wt % silicon.

4. The composition of any one of the preceding claims, wherein the aluminium-silicon alloy comprises less than 1 1 wt % silicon and optionally no more than 10.5 wt% silicon.

5. The composition of claim 1 , wherein the aluminium-silicon comprises at least 0.16 wt% iron.

6. The composition of claim 5, wherein the aluminium-silicon alloy comprises 0.30 wt% iron.

7. The composition of any previous claim, wherein the amount of manganese in the composition is determined by an iron to manganese ratio of at least about 0.2 and at most about 0.8.

8. The composition of claim 7, wherein the ratio of iron to manganese is at least 0.3, suitably at least 0.4, optionally 0.5, and up to 0.75.

9. The composition of claims 7 and 8, wherein the iron to manganese ratio is set at a level to ensure that majority of iron-containing intermetallic phase particles assume a polyhedral morphology within the microstructure of the alloy.

10. The composition of any previous claim, wherein the aluminium-silicon alloy comprises less than 0.1 wt% of magnesium and/or is substantially free of elements such as: molybdenum and zirconium.

1 1 . The composition of any previous claim, wherein the composition is heat treated.

12. The composition of claim 1 1 , wherein the heat treatment occurs at a temperature of at least around 350 °C, optionally at least around 360 °C, suitably up to around 390 °C.

13. The composition of claim 12, wherein the heat treatment occurs at a temperature of up to at most around 385 °C.

14. A method of manufacturing an aluminium-silicon alloy composition that is suitable for use in automotive and aeronautical castings, the method comprising adding to a source of aluminium that comprises at least 0.16 wt% iron, the following elements selected from:

(c) silicon, wherein the silicon is added at an amount of at least 8 wt% and at most 12 wt% of the total alloy mixture; and

(d) manganese, wherein the amount of manganese is determined by an iron to

manganese ratio of at least about 0.2 and at most about 0.8.

15. The method of claim 14, wherein the method comprises the additional step of forming the alloy into a die casting and heat treating the die casting.

16. The method of claim 15, wherein the heat treatment occurs at a temperature of at least around 350 °C, optionally at least around 360 °C, suitably up to around 390 °C.

17. The method of claim 15, wherein the heat treatment occurs at a temperature of up to at most around 385 ^<€.

18. The method of any of claims 14 to 17, wherein the ratio of iron to manganese is maintained at least 0.3, suitably at least 0.4, optionally 0.5, and up to 0.75.

19. The method of any of claim 14 to 18, wherein the aluminium comprises at least 0.30 wt% iron.

20. The method of any of claims 14 to 19, wherein the silicon is added to a final level of at least 8.5 wt% silicon, optionally about 9 wt% silicon, more optionally around 10 wt % silicon.

21 . A die casting manufactured from the aluminium silicon alloy of any of claims 1 to 13.

22. The die casting of claim 21 wherein the casting constitutes a part or component that is comprised within the body, chassis, powertrain, sub-frame or suspension system of a motor vehicle.

23. A method of die casting a component comprising, forming a die mould that defines the configuration of the component, injecting the molten aluminium-silicon alloy of any of claims 1 to 13 into the die mould and allowing the alloy to cool to form a solid die cast component.

24. The method of claim 23, wherein the method further comprises the step of heat treating the component.

25. The method of claim 24, wherein the heat treatment occurs at a temperature of at least around 350 °C, optionally at least around 360 °C, suitably up to around 390 °C.

26. A motor vehicle that comprises a part that includes or is comprised of a part or component manufactured from an aluminium-silicon alloy of any of claims 1 to 13.

27. Use of an aluminium-silicon alloy comprising an iron content of at least 0.16 wt% and a manganese content that is greater than the amount of iron present in the composition, for manufacturing a die cast part for a motor vehicle.

28. The use of claim 27, wherein the aluminium-silicon alloy comprises at least 0.16 wt% at most around 0.30 wt % iron.