EP4619561A1

EP4619561A1 - Multicomponent aluminium alloys with improved hot cracking properties and reduced porosity

Info

Publication number: EP4619561A1
Application number: EP23806302.8A
Authority: EP
Inventors: Jon Mikel Sanchez Severino; Maider Garcia de Cortazar; Haize Galarraga; Pedro Egizabal Luzuriaga; Frank Girot Mata
Original assignee: Euskal Herriko Unibertsitatea; Fundacion Tecnalia Research and Innovation
Current assignee: Euskal Herriko Unibertsitatea; Fundacion Tecnalia Research and Innovation
Priority date: 2022-11-16
Filing date: 2023-11-16
Publication date: 2025-09-24
Also published as: CN120225705A; EP4372114A1; WO2024105188A1

Abstract

The invention relates to new multicomponent aluminium alloys, with certain proportions of zinc, copper, magnesium and silicon; these alloys have fine microstructures, which allow their processability by means of different manufacturing techniques, including technologies where the rapid solidification of the process presents hot cracking problems and processes where porosity is generated. The invention also relates to the use of the alloys for the manufacture of articles by means of near net shape manufacturing techniques, and to articles comprising said alloys.

Description

MULTICOMPONENT ALUMINIUM ALLOYS WITH IMPROVED HOT CRACKING PROPERTIES AND REDUCED POROSITY

Field of the invention

The present invention relates to new multicomponent aluminium alloys, with certain proportions of zinc, copper and magnesium, as well as with a silicon content; these alloys have fine microstructures, which allow their processability by means of different manufacturing techniques, including technologies where the rapid solidification of the process presents hot cracking problems and processes where porosity is generated. The fine microstructure of these new alloys is made up of a saturated solid solution as a matrix and an interdendritic region formed by eutectic compounds.

State of the art

Aluminium is a light metal with a density of 2.70 g/cm³, and its alloys have lower mechanical properties than those of steel, although they have an excellent strength-to- weight ratio. Therefore, they are used when the weight factor is relevant, such as, for example, in aeronautical and automotive applications.

Aluminium alloys can be subdivided into two large groups, for forging and casting, depending on the manufacturing process.

Alloys for forging, that is, alloys used for the manufacture of sheets, films, extruded profiles, rods and wires, are classified according to the alloying elements they contain, based on a four-digit numerical code. They can be further subdivided into two groups, heat-treatable alloys and non-heat-treatable alloys; these latter alloys cannot be precipitation hardened and can only be cold worked to increase their strength.

Aluminium alloys for casting are characterised by their good castability, fluidity and mould feeding qualities, as well as by the optimisation of their properties of strength and toughness or corrosion resistance. To improve strength properties, the parts are cooled in moulds that allow high cooling rates. Nevertheless, these alloys are relatively limited in terms of their mechanical properties.

Some additive manufacturing techniques that are becoming increasingly relevant, such as L-PBF (laser powder bed fusion), L-DED (laser directed energy deposition) or WAAM (wire arc additive manufacturing), together with other more conventional processes, such as welding processes or pressure die casting (HPDC or high pressure die casting), involve process conditions with high cooling rates, generally greater than 50 °C/s. These cooling rates make it impossible to process some high- strength aluminium alloys. Commercial series of high strength or precipitation hardenable aluminium, for example, those belonging to the 2xx.x (Al-Cu) or 7xx.x (Al- Zn) series, were specifically developed for extrusion, rolling and forging processes, manufacturing processes with their corresponding intrinsic process characteristics, starting from ingots and slabs manufactured with solidification rates of the order of 3 °C/s or less. The processing of these alloys with higher cooling rates generates problems such as hot cracking, porosity, etc.

JPH05179384A discloses an aluminium alloy, based on the 7000 series, comprising 3 to 22% Si, 0.2 to 5% Cu, 1 .2 to 6% Mg and 5 to 15% Zn, which is described as exhibiting good wear resistance, coefficient of thermal expansion and mechanical strength. Nevertheless, this alloy is necessarily manufactured by a different type of process, a spray deposition method.

Therefore, there remains a need in the state of the art to achieve high-strength alloys that can be processed by techniques that involve cooling rates during solidification greater than 50 °C/s, but with low susceptibility to hot cracking and porosity.

The present invention provides high-strength alloys which can be processed by techniques that involve cooling rates during solidification greater than 50 °C/s due to their low susceptibility to hot cracking and porosity.

Most high-strength commercial aluminium alloys used in the automotive or aerospace industries owe their high mechanical properties to precipitation hardening. Precipitation hardening consists of the formation of small and dispersed precipitates of a second phase within the aluminium matrix, usually by heat treatment, improving the hardness of the alloy. These alloys were designed for conventional processes, such as forging, which, although they are susceptible to precipitation hardening, and therefore have better mechanical properties, are not processable by most additive manufacturing techniques, as they are prone to hot cracking.

Additive manufacturing is a manufacturing concept that brings together a series of manufacturing technologies based on the deposition of material layer after layer, which allows solid three-dimensional objects to be produced. In contrast to traditional metal manufacturing techniques (subtractive techniques), this set of techniques has properties intrinsic to the production process that affect the final properties of the manufactured part. Several authors have estimated that in additive manufacturing techniques such as L-PBF, the cooling rate of aluminium alloys can reach rates of between 1.25 x 10⁶ °C/s and 6.17 x 10⁶ °C/s [Li, Y et al., Mater. Des. 2014, 63, 856-867], Furthermore, there are also some conventional techniques for the production of parts such as HPDC that can reach up to 75 °C/s [Karkkainen, M et al., Miner. Met. Mater. Ser. 2017, Part F6, 457- 464], and, therefore, they can also present hot cracking problems.

The susceptibility to hot cracking of precipitation hardenable alloys leads to the need for new aluminium alloys specifically designed to be able to be processed under the working conditions of rapid solidification manufacturing techniques. For example, 7XXX series commercial alloys present problems upon being processed by WAAM and L-PBF: alloys manufactured by WAAM present gas pores [Kohler, M et al.; Metals (Basel). 2019, 9, 5; Sokoluk, M et al.; Nat. Commun. 2019, 10 (1); Eimer, E et al., Weld. World 2020, 64, 1313-1319], and alloys processed by L-PBF present hot cracking [Aversa, A et al., Materials (Basel), 2019, 12; DebRoy, T et al., Prog. Mater. Sci. 2018, 92, 112-224; Galy, C et al.; Addit. Manuf. 2018, 22, 165-175], deteriorating their mechanical properties.

Hot cracking arises because high cooling rates generate local stresses on a microstructural level during aluminium solidification that cause the occurrence of microcracks and affect the final mechanical properties. This effect is most evident in precipitation hardenable alloys, for example, those belonging to the 2xx.x (Al-Cu) or 7xx.x (Al-Zn) series. Hot cracking has meant that there are few aluminium alloys that can be processed by quenching techniques. The most used series to date are of the AISi12 or AISil OMg type, which are alloys developed for casting. This is because the eutectic or near-eutectic (Al-Si) composition of these alloys allows the solidification range to be reduced, decreasing susceptibility to hot cracking. These alloys are mostly made up of an aluminium matrix, reinforced by eutectic Si. The mechanical properties of these alloys, such as hardness or strength, are considerably lower than the properties of alloys of the 2xx.x (Al-Cu) or 7xx.x (Al-Zn) series or of precipitation hardenable alloys.

There are cases of specific commercial alloys designed for additive manufacturing that are resistant to hot cracking with high mechanical properties, for example, Scalmalloy® and A20X™, that have been able to be processed by different additive manufacturing techniques such as L-PBF and/or L-DED. These alloys owe a large part of their properties to the high presence of expensive elements such as Sc, Cu and Ag in their composition.

In the state of the art, there are also published studies and results about attempts to obtain improved aluminium alloys. For example, disclosed in patent application US 2011/0044843 A1 are alloys that were resistant to hot cracking when manufactured by additive manufacturing; to obtain a hardness between 165 HV and 184 HV, they had to be subjected to a T7 heat treatment. The disclosed and studied alloys can be divided into two families: Al-Cu-Mg-Zn-Zr and Al-Cu-Mg-Ag-Zr-Er-Y-Yb.

Summary of the invention

The present invention relates to new alloys, with a unique and determined chemical composition, which have a low susceptibility to hot cracking and porosity, and high hardness, without the need for heat treatments. These are high-strength alloys and can be processed by techniques that involve solidification with quenching (> 50 °C/s), without crack formation.

Specifically, the present invention relates to aluminium alloys, characterised in that they comprise: between 4.4 and 5.3% by weight of zinc, between 1 .7 and 1 .9% by weight of copper, between 1.5 and 2.1% by weight of magnesium and between 2 and 12% by weight of silicon.

Optionally, the aluminium alloys of the present invention may additionally comprise one or more of: between 0.003 and 1 .0% by weight of boron, between 0.08 and 0.3% by weight of titanium, between 0.1 and 0.4% by weight of manganese, between 0.1 and 0.3% by weight of chromium, up to 1 .0% by weight of silver, between 0.01 and 0.02% by weight of nickel, and up to 0.01% zirconium. The balance up to 100 % by weight of the alloy is aluminium.

It additionally relates to the use of such aluminium alloys for the preparation of an article by near net shape manufacturing techniques.

Likewise, the invention relates to an article comprising an aluminium alloy as defined above, or consisting of same.

Description of the figures

Figure 1 : Cross-section of the reference alloy and alloys manufactured by WAAM; Figure 1 a: represents a reference alloy AIZn5.5MgCu and 3 alloys according to the invention, 2.4% Si, 3.9% Si and 7.0% Si; Figure 1 b represents a reference alloy AIZn4.4Mg3.4Cu1.8. Important differences in their microstructures may be observed.

Figure 2: Micrograph of the microstructure of the alloy with 7.0% Si by WAAM.

Figure 3: Cross-section of the molten bath or melt pool of the alloys object of this invention and reference alloys manufactured by L-DED.

Figure 4: Detail of the microstructure of reference alloy AIZn5.5MgCu processed by laser with defects and transgranular cracks.

Figure 5: Micrograph showing the surface area of the a-AI matrix and the eutectic region.

Figure 6: Representation of the solidification curves of some alloys according to the present invention, using the Thermo-Calc software Scheil-Gulliver model, and reference alloys.

Figure 7: Solidification curves of some alloys according to the present invention and of alloy AIZn5.5MgCu, in the critical solidification range.

Description of the invention

These new alloys are a multicomponent aluminium alloy, with nominal formula AIZn4.9Cu1.8Mg2.1 and a silicon (Si) content between 2 and 12% by weight, preferably between 2.4 and 7.1% by weight, for example, 2.4, 3.9 or 7.03% by weight of silicon.

In that sense, according to a first object, the present invention relates to an aluminium alloy, characterised in that it comprises: between 4.4 and 5.3% by weight of zinc, between 1 .7 and 1 .9% by weight of copper, between 1.5 and 2.1% by weight of magnesium, between 2 and 12% by weight of silicon. Optionally, the aluminium alloy according to the invention may further contain one or more of: between 0.003 and 1 .0% by weight of boron; between 0.08 and 0.3% by weight of titanium; between 0.1 and 0.4% by weight of manganese; between 0.1 and 0.3% by weight of chromium; up to 1 .0% by weight of silver; between 0.01 and 0.02% by weight of nickel; up to 0.01% by weight of zirconium.

The balance up to 100 % by weight of the alloy is aluminium.

According to a particular embodiment of the invention, the aluminium alloy comprises:

4.9% by weight of zinc,

1 .8% by weight of copper,

2.1% by weight of magnesium, between 2 and 12% by weight of silicon. According to a further particular embodiment of the invention, the aluminium alloy comprises:

5.0% by weight of zinc,

1 .8% by weight of copper,

1 .7% by weight of magnesium, between 2 and 2.4 % by weight of silicon.

According to another particular embodiment of the invention, the aluminium alloy comprises:

5.2% by weight of zinc,

1 .85% by weight of copper,

2.4% by weight of magnesium, between 3.5 and 7, preferably between 3.9 and 4.9 % by weight of silicon.

According to an additional particular embodiment of the invention, the aluminium alloy comprises:

5.2% by weight of zinc,

1 .8% by weight of copper,

1 .5% by weight of magnesium, between 4.9 and 7% by weight, preferably 7 % of silicon.

According to particular embodiments of the invention, the silicon content is between 2.0 and 7 % by weight, or between 2.4 and 7% by weight, or between 2.4 and 4.9% by weight, or between 3.5 and 7% by weight, or between 3.9 and 7% by weight, or between 4.9 and 7% by weight, or between 4.9 and 12% by weight, or between 7 and 12% by weight, or between 1.5 and 12 % bey weight, or between 10.5 and 11 ,2 % by weight.

According to particular embodiments, one or more of the optional components may be contained in the following amounts: between 0.003 and 0.05, preferably between 0.003 and 0.01 % by weight of boron; between 0.08 and 0.2% by weight of titanium; between 0.3 and 0.4% by weight of manganese; between 0.2 and 0.3% by weight of chromium; between 0.01 and 0.015% by weight of nickel.

Another object according to the present invention is the use of an aluminium alloy as defined above for the preparation of an article by near net shape manufacturing techniques. These techniques can be selected from additive manufacturing, forging, welding and casting, although they are not limited to the above.

The invention also relates to an article comprising or consisting of an aluminium alloy as defined above.

Such a casting article is preferably selected from casings and structures for mobile telephones (including smartphones) and laptop computers, engine blocks in vehicles, such as automobiles, gearbox housings in vehicles, for example, aircraft, vehicle tyres, seat frames in vehicles, such as aircraft, battery boxes for electric vehicles, etc.

The multicomponent aluminium alloys of the present invention have the following features:

• reduced solidification range (< 40 °C), when the solid fraction (f_s) is close to 1

• precipitation of eutectic compounds (between 10 and 30% of the volume of the microstructure)

• fine microstructure (SDAS < 20 pm; SDAS = secondary dendrite arm spacing

• high hardness without the need for heat treatment (> 110 HV)

• less susceptibility to hot cracking and porosity formation

As will be further illustrated in the Examples, the multicomponent aluminium alloys according to the present invention present optimised solidification curves to reduce susceptibility to hot cracking, and the reduction of the solidus temperature to improve their fluidity during the last stage of solidification. The particular compositions of these alloys have allowed a eutectic microstructure to form, maintaining the hardness of high- strength commercial alloys. It should be noted that among the composition of these alloys there are no critical, expensive or hazardous elements frequently present in other alloys of the state of the art, such as, for example, Sc, Be, Li, Y, etc., and that the high hardness of the alloys has been achieved without the need for subsequent heat treatments.

Although the alloys according to the present invention are qualitatively based on Al-Zn-Mg-Cu (7xxxx series) type alloys, they differ quantitatively from any existing alloy. The alloys according to the present invention include a high amount of silicon, unlike the norm for the alloy

AIZn5.5MgCu, a very common alloy of the Al-Zn-Mg-Cu type alloys and used as a reference in the Examples. In Figures 6 and 7, the difference can be seen in the curves of susceptibility to cracking on the solidification between the AIZn5.5MgCu alloy and the alloys according to the present invention. This difference in the curve is due to the compositional chemical difference of the alloys.

Apart from the advantages of a reduced susceptibility to cracking and porosity of the alloys according to the present invention when they are manufactured by technologies that involve solidifications with quenching, their fine microstructure and hardness, it has surprisingly been found that the alloys do not form intermetallic compounds, especially compounds with acicular morphology. Usually, the increase in the number of elements in aluminium alloys leads to the occurrence of intermetallic compounds. Increasing the number of elements in aluminium alloys usually promotes the precipitation of compounds of this type; for example, in the case of aluminium alloys made up of Si, there is typically a formation of ternary compounds with acicular morphology of the AI-(Fe, Mn, Ni, etc.)-Si type, which are considered detrimental to the properties of the final alloy, and could affect the fineness of the grain. The formation of intermetallic compounds during the last stages of solidification would increase the susceptibility to hot cracking of alloys, a phenomenon that has been prevented with the alloys of the present invention.

Likewise, the alloys according to the present invention have surprisingly been found to have a high tolerance to contaminating elements.

Another surprising result is the occurrence of few phases in the final structure: obtaining a structure formed mainly by two phases, an a-AI matrix and an interdendritic space formed by a Si eutectic, has been detected. What would be typical is that, by applying the Gibbs phase rule, an alloy made up of N elements could have up to N + 1 phases. The stabilisation of a greater number of phases, especially if transition metals are used in aluminium alloys, is the most typical [Sanchez, J.M. et al., Metals (Basel). 2018, 8, 167; Sanchez, J.M. et al., Sci. Rep. 2019, 9, 6792; Sanchez, J.M. etal., J. Mater. Res. Technol. 2018, 1-9].

Examples

The following examples serve to further describe and illustrate the present invention, but in no way should they be construed as limiting the scope of the invention.

Example 1 - Preparation of alloys according to the invention.

Alloys have been prepared according to the invention, which alloys have the following elemental composition:

Table 1

Alloys 2.4-Si, 3.9-Si and 7.0-Si defined in Table 1 have been processed using the following manufacturing techniques: WAAM and L-DED.

EXAMPLE 1.1 - Alloys processed by WAAM

Alloys 2.4-Si, 3.9-Si and 7.0-Si have been manufactured in a WAAM TIG/MAG flexible additive manufacturing cell at 150 Amps (150 A). Figure 1 shows micrographs of the cross-section of the weld bead of the alloys according to the invention, as well as of the AIZn5.5MgCu (Fig. 1 a) and the AIZn4.4Mg3.4Cu1 .8 (Fig. 1 b) alloys, used as a reference. Al-Zn-Mg-Cu alloys are generally alloys that present problems when processed by WAAM, due to the formation of gas pores that deteriorate their mechanical properties [Guo, Y et al., Virtual Phys. Prototyp. 2022, 17, 649-661]. As can be seen in Figure 1 , welding defects are only observed in reference alloy AIZn5.5MgCu. The alloys according to the present invention show a pore-free surface. Furthermore, none of the alloys according to the invention show cracks indicating susceptibility to cracking when processed by WAAM; however, commercial alloy AIZn5.5MgCu used as a reference does show cracks.

Based on these images, it is shown that the alloys according to the present invention show a fineness in their microstructure, after being processed by quenching techniques, as well as the precipitation of eutectic compounds. By way of example, Figure 2 shows the micrograph of the microstructure of alloy 7.0-Si. It is observed that said alloy is made up of an aluminium matrix, with a mean SDA spacing less than 8 pm in all cases, with the precipitation of fine eutectic compounds. In the microstructure, only the Al and Si eutectic can be distinguished.

The mean SDA values of the alloys according to the present invention are indicated in Table 2:

Table 2. SDA values of the alloys according to the invention

EXAMPLE 1.2 - Alloys processed by L-DED

Alloys 2.4-Si, 3.9-Si and 7.03-Si have been manufactured by laser directed energy deposition or L-DED technology. Two reference alloys have also been processed, the alloy AISilOMg and AIZn5.5MgCu, respectively, with zero and high susceptibility to hot cracking. Micrographs of the cross-section of the melt pool of the alloys object of this invention and of the reference alloys are shown in Figure 3. As can be observed in the figure, all the samples corresponding to the alloys according to the present invention have a crack-free surface.

In contrast, laser-processed reference alloy AIZn5.5MgCu shows microporosity and crack defects, as can be seen in Figure 4, where the cracks are shown in detail, in different regions of the melt area. In contrast, Figure 4 shows the micrograph of the microstructure of the alloy with 7.0% Si. The alloy is made up of an aluminium matrix with a mean SDA spacing less than 4 pm in all cases, with the precipitation of fine eutectic compounds. Only the Al and Si eutectic (fine eutectic compounds) is distinguished.

The mean SDA values of the alloys studied in this Example 1.2 are summarised in Table 3:

Table 3. SDA values of the alloys studied in this example.

Therefore, it is shown that the alloys according to the present invention have a fine microstructure reinforced with eutectic compounds in the interdendritic space, which has allowed all alloys to be manufactured without hot cracking problems.

Example 2 - Hardness

The hardness of the alloys has been measured according to the ISO 6507-1 “Metallic Materials - Vickers Hardness Test” standard and has been compared with reference alloys AISil OMg and AIZn5.5MgCu manufactured by the traditional method with moderate cooling and by additive manufacturing with quenching. To obtain the hardness values, an FV-700 model durometer (Future-Tech, Kawasaki, Japan) under the load of 10 kgf has been used. At least five random surface hardness measurements have been taken on each sample, with a retention time of the indenter in the tested sample of 10 s.

All the alloys object of this invention have obtained a hardness higher than that of reference alloy AISilOMg and higher than that of reference alloy AIZn5.5MgCu when manufactured by additive manufacturing. Alloy AIZn5.5MgCu has been shown to be susceptible to hot cracking when manufactured by additive manufacturing, with the occurrence of cracks that have decreased the hardness of the alloy. The hardness of this alloy is 145 HV 10 in its commercial forging format, these values being similar to those that can be attained with the addition of 7.0% Si.

Therefore, a combination of the solidification and microstructural properties of alloy AISil OMg with the hardness properties of alloy AIZn5.5MgCu has been obtained. It should be noted that, like alloy AISilOMg, the hardness of the alloys object of the invention have increased when manufactured by additive manufacturing with respect to that obtained by conventional manufacturing methods, as opposed to what happens with alloy AIZn5.5MgCu.

The hardness values obtained are indicated in Table 4:

Table 4. Hardness of the preferred alloys of the present invention and reference alloys.

¹ as cast

² commercial wrought alloy

³ sample with pores, could not be measured (Fig. 1) ⁴ IACS = International Annealed Copper Standard

[C] publication US10941473B2

Example 3: Solidification curves of the alloys according to the invention

Alloys susceptible to hot cracking can be identified from their solidification curves. Generally, these alloys present large solidification ranges between liquidus and solidus temperatures and an abrupt change or turnover in the solidification curves at high fractions of solids. The different models for hot cracking determine that this phenomenon occurs when the solid fraction is greater than 0.8 [Eskin, D.G. et al., Prog. Mater. Sci. 2004, 49, 629-711], and when tensile stresses exceed the resistance of the material in the semisolid state. The abrupt change in the solidification curve is normally associated with increased levels of solute elements that are distributed throughout the liquid to a high degree during solidification. The decreased solid fraction (f_s) at which the reduction of the difference between the solidus and liquidus temperatures occurs decreases the tendency for hot cracking in alloys [Martin, J.H. et al., Nature 2017, 549, 365-369]. In Figure 6, the solidification curves of alloys according to the present invention have been represented, using the Thermo-Calc software Scheil-Gulliver model, specifically for the following alloys:

1. AIZn4.9Cu1.8Mg2.1 Si2.4 2.4% Si

2. AIZn4.9Cu1.8Mg2.1Si3.9 3.9% Si

3. AIZn4.9Cu1.8Mg2.1 Si7.0 7.0% Si

The graph also includes two reference alloys, alloy AISiWMg (ENAC-43000) since it is representative of alloys not susceptible to cracking, and alloy AIZn5.5MgCu (AA7075) since it is a precipitation hardenable alloy susceptible to hot cracking. Lastly, the composition of the designed alloy has also been calculated, but without Si (0% Si). As can be seen, alloy 0% Si presents a solidification curve similar to alloys susceptible to hot cracking, with a sharp turnover in the last stages of solidification. However, it does represent a notable improvement over AIZn5.5MgCu.

As can be observed, the effects of Si cause the curve to gradually flatten, in addition to the turnover moving back towards a solid fraction closer to that of alloy AISiWMg. Furthermore, with the incorporation of more than 2.4% of Si, there is a drop in the solidus temperature, which improves the fluidity of the material during solidification.

Example 4: Critical solidification range

A more specific and complementary way to quantify the susceptibility to hot cracking of aluminium alloys is to represent the diagrams as a function of temperature and the square root of the solid fraction (T ° VS ^/Ts) in a certain range, called the critical solidification range. In Figure 7, the slope of the alloys object of the present invention has been quantified. A smaller slope indicates a lower susceptibility to hot cracking.

To that end, alloys can be evaluated by means of the index for the susceptibility of an alloy to hot cracking during the last stage of solidification by [Kou, S., Acta Mater. close to 1

More in detail, the critical solidification range is defined when f_s is between 0.87 and 0.94, in other words, when is between 0.933 and 0.970.

The largest slope, therefore, the highest tendency to hot cracking, is held by alloy AIZn5.5MgCu, followed by alloy 0% Si (AIZn4.9Cu1.8Mg2.1), and finally, with a similar susceptibility, alloys 2.4% Si, 3.9% Si and 7.0% Si. The representative points of the solidification curves according to the criterion used for the design of the alloys are summarised in Table 5. As can be seen, the solidification range of the alloys object of this invention has been reduced to one third with respect to that of the alloy used as a reference alloy susceptible to cracking.

Table 5. Representative points of the solidification curves Example 5: Microstructure of an alloy according to the invention processed by computational digital image analysis techniques

By way of example, Figure 5 shows the microstructure processed by computational digital image analysis techniques of the alloy with 7.03% Si. The surface of the a-AI matrix, which represents a minimum of 75% in the invention, is observed in light grey. The interdendritic region, which is made up of eutectic compounds, which is a maximum of 25% in the alloy of the present invention, is observed in black.

Claims

1. An aluminium alloy, characterised in that it comprises: between 4.4 and 5.3% by weight of zinc, between 1 .7 and 1.9% by weight of copper, between 1.5 and 2.1% by weight of magnesium, between 2 and 12% by weight of silicon, optionally, between 0.003 and 1.0% by weight of boron, optionally, between 0.08 and 0.3% by weight of titanium, optionally, between 0.1 and 0.4% by weight of manganese, optionally, between 0.1 and 0.3% by weight of chromium, optionally, up to 1.0% by weight of silver, optionally, between 0.01 and 0.02% by weight of nickel, optionally, between up to 0.01% zirconium, and balance of aluminium up to 100% by weight.

2. The aluminium alloy according to claim 1 , characterised in that it comprises boron in an amount of between 0.003 and 0.05 % by weight, preferably between 0.003 and 0.01% by weight.

3. The aluminium alloy according to any one of claims 1 and 2, characterised in that it comprises titanium in an amount of between 0.08 and 0.2% by weight.

4. The aluminium alloy according to any one of claims 1 to 3, characterised in that it comprises manganese in an amount of between 0.3 and 0.4% by weight.

5. The aluminium alloy according to any one of claims 1 to 4, characterised in that it comprises chromium in an amount of between 0.2 and 0.3% by weight.

6. The aluminium alloy according to any one of claims 1 to 5, characterised in that it comprises nickel in an amount of between 0.01 and 0.015% by weight.

7. The aluminium alloy according to any one of claims 1 to 6, characterised in that it comprises

4.9% by weight of zinc,

1 .8% by weight of copper,

2.1% by weight of magnesium, between 2 and 12% by weight of silicon.

8. The aluminium alloy according to any one of claims 1 to 7, characterised in that it comprises between 2.0 and 7% by weight of silicon.

9. The aluminium alloy according to any one of claims 1 to 8, characterised in that it comprises between 2.0 and 2.4% by weight of silicon.

10. The aluminium alloy according to any one of claims 1 to 8, characterised in that it comprises between 3.5 and 7 % by weight of silicon, preferably between 3.9 and 7 % by weight.

11 . The aluminium alloy according to any one of claims 1 to 7, characterised in that it comprises between 3.5 and 7 % by weight of silicon, preferably between 3.9 and 7 % by weight.

12. The aluminium alloy according to any one of claims 1 to 10, characterised in that it comprises between 10.5 and 12 % by weight of silicon, preferably between 10.5 and

11 .2 % by weight.

13. Use of an aluminium alloy as defined in any one of claims 1 to 12 for the preparation of an article by near net shape manufacturing techniques.

14. The use of an aluminium alloy according to claim 13, wherein the manufacturing technique without the need for subsequent cuts is selected from additive manufacturing, linear and rotary friction welding, pressure die casting, sand casting, investment casting or injection moulding.

15. An article comprising an aluminium alloy as defined in any one of claims 1 to 12.

16. An article consisting of an aluminium alloy as defined in any one of claims 1 to 12.

17. The article according to claim 15 or 16, selected from casings and structures for mobile telephones and laptop computers, engine blocks in automobiles, gearbox housings, vehicle tyres, seat frames in vehicles, battery box for electric vehicles.