Multi-component aluminum alloys with improved hot crack properties and reduced porosity

Abstract

The present invention relates to a novel multi-component aluminum alloy having a proportion of zinc, copper, magnesium and silicon; these alloys have a fine microstructure, which allows for their processability through different manufacturing techniques, including techniques in which rapid solidification of the process exhibits a hot crack problem and processes in which voids are created. The invention also relates to the use of the alloy for manufacturing an article by means of a near-net-size forming manufacturing technique, and to an article comprising said alloy.

Description

Technical Field

[0001] The present invention relates to new multicomponent aluminum alloys having a certain proportion of zinc, copper, and magnesium and having a silicon content; these alloys have a fine microstructure, which allows their workability by different manufacturing techniques including rapid solidification processes where hot cracking problems occur and processes where porosity is generated. The fine microstructure of these new alloys consists of interdendritic regions formed by a saturated solid solution as the matrix and eutectic compounds. Background Art

[0002] Aluminum is a light metal with a density of 2.70 g / cm 3 and the mechanical properties of its alloys are lower than those of steel, but they have an excellent strength-to-weight ratio. Therefore, they are used, for example, in aerospace and automotive applications when the weight factor is valuable.

[0003] Aluminum alloys can be subdivided into two large groups for forging and casting according to the manufacturing process.

[0004] Alloys for forging, i.e., alloys for manufacturing sheets, membranes, extruded profiles, bars, and wires, are classified according to a four-digit code based on the alloying elements they contain. 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.

[0005] Aluminum alloys for casting are characterized by their good castability, fluidity, and die-feeding quality, as well as the optimization of properties such as strength and toughness or corrosion resistance. To improve the strength properties, the components are cooled in molds that allow high cooling rates. However, these alloys are relatively limited in terms of their mechanical properties.

[0006] Some additive manufacturing techniques that are becoming increasingly valuable, such as L-PBF (laser powder bed fusion), L-DED (laser directed energy deposition), or WAAM (wire arc additive manufacturing), as well as other more conventional processes such as welding processes or pressure casting (HPDC or high-pressure die casting), involve process conditions with high cooling rates (usually greater than 50 °C / second). These cooling rates make it impossible to process some high-strength aluminum alloys. Commercial series of high-strength or precipitation-hardenable aluminum, such as those belonging to the 2xx.x (Al-Cu) or 7xx.x (Al-Zn) series, are specifically developed for extrusion, rolling, and forging processes, starting from ingots and slabs manufactured at solidification rates on the order of 3 °C / second or less. Processing these alloys at higher cooling rates results in problems such as hot cracking and porosity.

[0007] JPH05179384A discloses an aluminum alloy based on the 7000 series, which contains 3% to 22% Si, 0.2% to 5% Cu, 1.2% to 6% Mg, and 5% to 15% Zn, and is described as exhibiting good wear resistance, coefficient of thermal expansion, and mechanical strength. However, this alloy must be manufactured by different types of processes (spray deposition method).

[0008] Therefore, in the prior art, there is still a need to achieve such high-strength alloys that can be processed by techniques involving cooling rates during solidification greater than 50 °C / second, but are less sensitive to hot cracking and porosity.

[0009] The present invention provides such high-strength alloys that, due to their low sensitivity to hot cracking and porosity, can be processed by techniques involving cooling rates during solidification greater than 50 °C / second.

[0010] Most high-strength commercial aluminum alloys used in the automotive or aerospace industries attribute their high mechanical properties to precipitation hardening. Precipitation hardening involves the formation of small and dispersed precipitates of a second phase, usually through heat treatment, within the aluminum matrix, improving the hardness of the alloy. These alloys are designed for conventional processes such as forging, but they are prone to precipitation hardening and thus have better mechanical properties and cannot be processed by most additive manufacturing techniques because they are prone to hot cracking.

[0011] Additive manufacturing is a manufacturing concept that combines a series of manufacturing techniques based on the layer-by-layer deposition of materials, which allows the production of solid three-dimensional objects. Compared with traditional metal manufacturing techniques (subtractive techniques), this set of techniques has characteristics inherent in the production process, which affect the final characteristics of the manufactured parts. Several authors estimate that in additive manufacturing techniques such as L-PBF, the cooling rate of aluminum alloys can reach a rate of 1.25×10 6 ℃ / s to 6.17×10 6 ℃ / s [Li, Y et al., Mater. Des. 2014, 63, 856 - 867]. In addition, there are some conventional techniques that can reach up to 75℃ / s for the production of parts such as HPDC [Karkkainen, M et al., Miner. Met. Mater. Ser. 2017, F6 part, 457 - 464], and therefore, they may also present the problem of hot cracking.

[0012] The sensitivity of precipitation-hardening alloys to hot cracking has led to the need for newly designed aluminum alloys that are specifically designed to be able to be processed under the working conditions of rapid solidification manufacturing techniques. For example, commercial alloys in the 7XXX series present problems when processed by WAAM and L-PBF: alloys manufactured by WAAM present porosity 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.

[0013] Hot cracking occurs because the high cooling rate generates local stresses at the microstructural level during aluminum solidification, which leads to the appearance of microcracks and affects the final mechanical properties. This effect is most pronounced in precipitation-hardenable alloys (e.g., those belonging to the 2xx.x (Al-Cu) or 7xx.x (Al-Zn) series). Hot cracking means that there are few aluminum alloys that can be processed by quenching techniques. The most used series so far are of the AlSi12 or AlSi10Mg type, which are alloys developed for casting. This is because the eutectic or near-eutectic (Al-Si) composition of these alloys allows reducing the solidification range and decreasing the sensitivity to hot cracking. These alloys are mostly composed of an aluminum matrix reinforced by eutectic Si. The mechanical properties (such as hardness or strength) of these alloys are significantly lower than those of alloys of the 2xx.x (Al-Cu) or 7xx.x (Al-Zn) series or precipitation-hardenable alloys.

[0014] There are cases of specific commercial alloys designed for additive manufacturing that have high mechanical properties and are resistant to hot cracking, such as and A20X TM which can be processed by different additive manufacturing techniques such as L-PBF and / or L-DED. These alloys owe most of their properties to the substantial presence of expensive elements such as Sc, Cu, and Ag in their composition.

[0015] In the prior art, there are also publicly available studies and results on attempts to obtain improved aluminum alloys. For example, alloys resistant to hot cracking when manufactured by additive manufacturing are disclosed in patent application US2011 / 0044843 A1; in order to obtain a hardness of 165 HV to 184 HV, they must undergo T7 heat treatment. The alloys disclosed and studied can be divided into two categories: Al-Cu-Mg-Zn-Zr and Al-Cu-Mg-Ag-Zr-Er-Y-Yb. Summary of the Invention

[0016] The present invention relates to new alloys with a unique and defined chemical composition, which have low sensitivity to hot cracking and porosity, and high hardness, without the need for heat treatment. These are high-strength alloys and can be processed by techniques involving solidification by quenching (>50 °C / second) without crack formation.

[0017] Specifically, the present invention relates to an aluminum alloy, characterized in that it comprises:

[0018] - 4.4 wt% to 5.3 wt% of zinc,

[0019] - 1.7 wt% to 1.9 wt% of copper,

[0020] - 1.5 wt% to 2.1 wt% of magnesium, and

[0021] - 2 wt% to 12 wt% silicon.

[0022] Optionally, the aluminum alloy of the present invention may additionally contain one or more of the following:

[0023] - 0.003 wt% to 1.0 wt% boron,

[0024] - 0.08 wt% to 0.3 wt% titanium,

[0025] - 0.1 wt% to 0.4 wt% manganese,

[0026] - 0.1 wt% to 0.3 wt% chromium,

[0027] - up to 1.0 wt% silver,

[0028] - 0.01 wt% to 0.02 wt% nickel, and

[0029] - up to 0.01% zirconium. The balance to 100 wt% of the alloy is aluminum.

[0030] It also relates to the use of such an aluminum alloy for the preparation of articles by near net shape forming manufacturing techniques.

[0031] Similarly, the present invention relates to articles comprising or consisting of the aluminum alloy as defined above. Description of the Drawings

[0032] Figure 1 : Cross-sections of the reference alloy and the alloy manufactured by WAAM; Figure 1 a: Represents the reference alloy AlZn5.5MgCu and three alloys according to the present invention (2.4% Si, 3.9% Si, and 7.0% Si); Figure 1 b represents the reference alloy AlZn4.4Mg3.4Cu1.8. Significant differences in their microstructures can be observed.

[0033] Figure 2 : Micrograph of the microstructure of the alloy with 7.0% Si by WAAM.

[0034] Figure 3 : Cross-section of the melt bath or molten pool of the alloy articles of the present invention and the reference alloy manufactured by L-DED.

[0035] Figure 4 : Details of the microstructure of the reference alloy AlZn5.5MgCu with defects and transgranular cracks by laser processing.

[0036] Figure 5: Micrograph showing the surface area of the α-Al matrix and eutectic regions.

[0037] Figure 6 : Representation of the solidification curves of some alloys according to the invention and control alloys using the Scheil-Gulliver model of Thermo-Calc software.

[0038] Figure 7 : Solidification curves of some alloys according to the invention and alloy AlZn5.5MgCu in the critical solidification range. Detailed Description

[0039] The present invention relates to new alloys with a unique and defined chemical composition, which have low sensitivity to hot cracking and porosity, and high hardness, without the need for heat treatment. These are high-strength alloys and can be processed by techniques involving solidification with quenching (>50 °C / second) without crack formation.

[0040] These new alloys are multi-component aluminum alloys with a nominal composition of AlZn4.9Cu1.8Mg2.1 and a silicon (Si) content of 2 wt% to 12 wt%, preferably 2.4 wt% to 7.1 wt%, for example 2.4 wt%, 3.9 wt% or 7.03 wt% of silicon.

[0041] In this sense, according to a first object, the present invention relates to an aluminum alloy, characterized in that it comprises:

[0042] - 4.4 wt% to 5.3 wt% of zinc,

[0043] - 1.7 wt% to 1.9 wt% of copper,

[0044] - 1.5 wt% to 2.1 wt% of magnesium,

[0045] - 2 wt% to 12 wt% of silicon. Optionally, the aluminum alloy according to the invention may further comprise one or more of the following:

[0046] 0.003 wt% to 1.0 wt% of boron;

[0047] 0.08 wt% to 0.3 wt% of titanium;

[0048] 0.1 wt% to 0.4 wt% of manganese;

[0049] 0.1 wt% to 0.3 wt% of chromium;

[0050] Up to 1.0 wt% of silver;

[0051] 0.01 wt% to 0.02 wt% of nickel;

[0052] Up to 0.01% by weight of zirconium.

[0053] The balance to 100% by weight of the alloy is aluminum.

[0054] According to a specific embodiment of the present invention, the aluminum alloy comprises:

[0055] - 4.9% by weight of zinc,

[0056] - 1.8% by weight of copper,

[0057] - 2.1% by weight of magnesium,

[0058] - 2% to 12% by weight of silicon.

[0059] According to another specific embodiment of the present invention, the aluminum alloy comprises:

[0060] - 5.0% by weight of zinc,

[0061] - 1.8% by weight of copper,

[0062] - 1.7% by weight of magnesium,

[0063] - 2% to 2.4% by weight of silicon.

[0064] According to another specific embodiment of the present invention, the aluminum alloy comprises:

[0065] - 5.2% by weight of zinc,

[0066] - 1.85% by weight of copper,

[0067] - 2.4% by weight of magnesium,

[0068] - 3.5% to 7%, preferably 3.9% to 4.9% by weight of silicon.

[0069] According to another specific embodiment of the present invention, the aluminum alloy comprises:

[0070] - 5.2% by weight of zinc,

[0071] - 1.8% by weight of copper,

[0072] - 1.5% by weight of magnesium,

[0073] - 4.9% to 7%, preferably 7% by weight of silicon.

[0074] According to a specific embodiment of the present invention, the silicon content is 2.0 wt% to 7 wt%, or 2.4 wt% to 7 wt%, or 2.4 wt% to 4.9 wt%, or 3.5 wt% to 7 wt%, or 3.9 wt% to 7 wt%, or 4.9 wt% to 7 wt%, or 4.9 wt% to 12 wt%, or 7 wt% to 12 wt%, or 1.5 wt% to 12 wt%, or 10.5 wt% to 11.2 wt%.

[0075] According to a specific embodiment, one or more optional components may be included in the following amounts:

[0076] 0.003 wt% to 0.05 wt%, preferably 0.003 wt% to 0.01 wt% of boron;

[0077] 0.08 wt% to 0.2 wt% of titanium;

[0078] 0.3 wt% to 0.4 wt% of manganese;

[0079] 0.2 wt% to 0.3 wt% of chromium;

[0080] 0.01 wt% to 0.015 wt% of nickel.

[0081] Another object of the present invention is the use of the aluminum alloy as defined above for the preparation of articles by near-net shape forming manufacturing techniques. These techniques may be selected from additive manufacturing, forging, welding, and casting, but they are not limited to the above.

[0082] The present invention also relates to articles comprising or consisting of the aluminum alloy as defined above.

[0083] Such cast articles are preferably selected from the housings and structures for mobile phones (including smart phones) and laptop computers, engine blocks in vehicles (such as cars), gearbox housings in vehicles (such as airplanes), vehicle tires, seat frames in vehicles (such as airplanes), battery boxes for electric vehicles, and the like.

[0084] The multi-component aluminum alloy of the present invention has the following characteristics:

[0085] · A reduced solidification range (<40 °C) when the solid fraction (f s ) is close to 1

[0086] · The precipitation of eutectic compounds (10% to 30% of the volume of the microstructure)

[0087] · A fine microstructure (SDAS < 20 μm; SDAS = secondary dendrite arm spacing)

[0088] · High hardness (> 110 HV) without the need for heat treatment

[0089] · Lower sensitivity to hot cracking and porosity formation.

[0090] As will be further illustrated in the examples, the multicomponent aluminum alloys according to the present invention exhibit an optimized solidification curve to reduce the sensitivity to hot cracking and a decrease in the solidus temperature to improve their fluidity during the final stage of solidification. The specific composition of these alloys allows for the formation of eutectic microstructures, maintaining the hardness of high-strength commercial alloys.

[0091] It should be noted that in the composition of these alloys, there are no critical, expensive or harmful elements that are often present in other alloys of the prior art, such as Sc, Be, Li, Y, etc., and the high hardness of the alloys is achieved without the need for subsequent heat treatment.

[0092] Although the alloys according to the present invention are qualitatively based on Al-Zn-Mg-Cu (7xxxx series) type alloys, they are quantitatively different from any existing alloys. The alloys according to the present invention differ from the specifications of the alloys and contain a large amount of silicon.

[0093] AlZn5.5MgCu is a very common alloy of the Al-Zn-Mg-Cu type alloy and is used as a control in the examples. In Figure 6 and Figure 7 it is possible to see the difference in the curves of the sensitivity to cracking during solidification between the AlZn5.5MgCu alloy and the alloys according to the present invention. This difference in the curve is due to the chemical differences in the composition of the alloys.

[0094] In addition to the advantages of the alloys according to the present invention in terms of their reduced sensitivity to cracking and porosity, their fine microstructure and hardness when manufactured by techniques involving quenching solidification, it has been unexpectedly found that the alloys do not form intermetallic compounds, especially compounds with a needle-like morphology. Generally, an increase in the number of elements in an aluminum alloy leads to the appearance of intermetallic compounds. An increase in the number of elements in an aluminum alloy usually promotes the precipitation of this type of compound; for example, in the case of an aluminum alloy composed of Si, a ternary compound of the Al-(Fe, Mn, Ni, etc.)-Si type with a needle-like morphology is usually formed, which is considered harmful to the properties of the final alloy and may affect the fineness of the grains. The formation of intermetallic compounds during the final stage of solidification will increase the sensitivity of the alloy to hot cracking (a phenomenon that has been prevented using the alloys according to the present invention).

[0095] Similarly, it has been unexpectedly found that the alloys according to the present invention have a high tolerance to contaminating elements.

[0096] Another unexpected result is the occurrence of few phases in the final structure: a structure mainly formed by two phases (α - A1 matrix and interdendritic spaces formed by Si eutectic) has been detected. Typically, by applying Gibbs phase rule, an alloy composed of N elements can have up to N + 1 phases. The stabilization of a larger number of phases (especially if transition metals are used in aluminum 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. et al., J.Mater.Res.Technol. 2018, 1 - 9].

[0097] Example

[0098] The following examples are used to further describe and illustrate the present invention, but they should in no way be construed as limiting the scope of the present invention.

[0099] Example 1 - Preparation of the alloy according to the present invention.

[0100] Alloys have been prepared according to the present invention, and the alloys have the following elemental compositions:

[0101] Table 1

[0102] Number Si Cu Mn Fe Mg Cr Ni Zn Ti B 2.4 - Si 2.39 1.79 0.352 0.32 1.73 0.304 0.01 4.98 0.087 0.003 3.9 - Si 3.92 1.85 0.329 0.33 2.08 0.286 0.004 5.24 0.072 0.003 7.0 - Si 7.03 1.67 0.399 0.32 1.54 0.277 0.01 5.16 0.194 0.003

[0103] The 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.

[0104] Example 1.1 - Alloy processed by WAAM

[0105] The alloys 2.4 - Si, 3.9 - Si, and 7.0 - Si have been manufactured at 150 amperes (150A) in a WAAM TIG / MAG flexible additive manufacturing unit. Figure 1 Micrographs of cross - sections of welds of the alloys according to the present invention and the AlZn5.5MgCu ( Figure 1 a) and AlZn4.4Mg3.4Cu1.8 (Figure 1b) alloys used as controls are shown. Al - Zn - Mg - Cu alloys are generally alloys that present problems when processed by WAAM due to the formation of pores that deteriorate their mechanical properties [Guo, Y et al., VirtualPhys.Prototyp. 2022, 17, 649 - 661]. As shown in Figure 1As can be seen, welding defects were observed only in the reference alloy AlZn5.5MgCu. The alloys according to the invention showed a pore-free surface. In addition, the alloys according to the invention did not show any cracks indicating sensitivity to cracking when processed by WAAM; however, the commercial alloy AlZn5.5MgCu used as a reference did show cracks.

[0106] Based on these images, it was shown that the alloys according to the invention showed the fineness of their microstructure and the precipitation of eutectic compounds after being processed by quenching techniques. For example, Figure 2 Micrographs of the microstructure of alloy 7.0 - Si are shown. It was observed that the alloy consisted of an aluminum matrix (in all cases, the average SDA spacing was less than 8 μm) and precipitates of fine eutectic compounds. In the microstructure, only the Al and Si eutectic could be seen.

[0107] The average SDA values of the alloys according to the invention are shown in Table 2:

[0108] Table 2. SDA values of the alloys according to the invention

[0109] Number SDAS (μm) - 150A 2.4% Si 5-8 3.9% Si 5-7 7.0% Si 4-8

[0110] Example 1.2 - Alloy processed by L - DED

[0111] Alloys 2.4 - Si, 3.9 - Si, and 7.03 - Si have been manufactured by laser directed energy deposition or L - DED techniques. Two reference alloys, alloy AlSi10Mg and AlZn5.5MgCu, which have zero sensitivity and high sensitivity to hot cracking respectively, were also processed. Micrographs of the cross - sections of the melt pools of the alloy articles of the invention and the reference alloys are shown in Figure 3 . As can be observed in the figure, all samples corresponding to the alloys according to the invention had crack - free surfaces.

[0112] In contrast, the laser - processed reference alloy AlZn5.5MgCu showed micropore and crack defects, as Figure 4 can be seen, where the cracks were shown in detail in different regions of the melt zone.

[0113] In contrast, Figure 4 Micrographs of the microstructure of the alloy with 7.0% Si are shown. The alloy consisted of an aluminum matrix (in all cases, the average SDA spacing was less than 4 μm) and precipitates of fine eutectic compounds. Only the Al and Si eutectic (fine eutectic compounds) were seen.

[0114] The average SDA values of the alloys studied in Example 1.2 are summarized in Table 3:

[0115] Table 3. SDA values of the alloys studied in this example.

[0116] Number SDAS (μm) - L - DED 2.4% Si 3-4 3.9% Si 3-4 7.0% Si 3-4

[0117] Therefore, it is shown that the alloys according to the present invention have a fine microstructure with eutectic compounds reinforcing in the interdendritic spaces, which allows all alloys to be manufactured without hot cracking problems.

[0118] Example 2 - Hardness

[0119] The hardness of the alloys has been measured according to the ISO 6507-1 "Metallic Materials - Vickers Hardness Test" standard and compared with the reference alloys AlSi10Mg and AlZn5.5MgCu manufactured by conventional methods with moderate cooling and by additive manufacturing with quenching. To obtain the hardness values, a FV-700 type hardness tester (Future-Tech, Kawasaki, Japan) has been used under a load of 10 kgf. At least five random surface hardness measurements have been carried out on each sample, with the dwell time of the indenter in the tested sample being 10 seconds.

[0120] All alloy articles of the present invention have obtained a hardness higher than that of the reference alloy AlSi10Mg and higher than that of the reference alloy AlZn5.5MgCu when manufactured by additive manufacturing. It has been shown that the alloy AlZn5.5MgCu is prone to hot cracking when manufactured by additive manufacturing, where the appearance of cracks reduces the hardness of the alloy. The hardness of this alloy in its commercial forged form is 145 HV 10, and these values are similar to those that can be obtained with the addition of 7.0% Si.

[0121] Therefore, a combination of the solidification and microstructure characteristics of the alloy AlSi10Mg and the hardness characteristics of the alloy AlZn5.5MgCu has been obtained. It should be noted that, contrary to what happens with the alloy AlZn5.5MgCu, the hardness of the alloy articles of the present invention when manufactured by additive manufacturing increases as with the alloy AlSi10Mg with respect to the hardness of the alloy articles obtained by conventional manufacturing methods.

[0122] The hardness values obtained are shown in Table 4:

[0123] Table 4. Hardness of the preferred alloys and reference alloys of the present invention.

[0124]

[0125] 1 As-cast

[0126] 2 Commercially forgeable alloy

[0127] 3 Sample with holes, cannot be measured ( Figure 1 )

[0128] 4 IACS = International Annealed Copper Standard

[0129] [C] Publication US10941473B2

[0130] Example 3: Solidification curve of the alloy according to the present invention

[0131] Alloys prone to hot cracking can be identified from their solidification curves. Typically, these alloys exhibit a large solidification range between the liquidus temperature and the solidus temperature, as well as a sudden change or inversion in the solidification curve at high solid fractions. 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 the tensile stress exceeds the resistance of the material in the semi - solid state. The sudden change in the solidification curve is usually associated with an increase in the level of solute elements highly distributed throughout the liquid during solidification. The reduced solid fraction (f s ) at the onset of a decrease in the difference between the solidus temperature and the liquidus temperature reduces the tendency for hot cracking in the alloy [Martin, J.H. et al., Nature 2017, 549, 365 - 369]. In Figure 6 , the solidification curves of the alloys according to the present invention were represented using the Thermo - Calc software Scheil - Gulliver model, especially for the following alloys:

[0132] 1. AlZn4.9Cu1.8Mg2.1Si2.4 2.4% Si

[0133] 2. AlZn4.9Cu1.8Mg2.1Si3.9 3.9% Si

[0134] 3. AlZn4.9Cu1.8Mg2.1Si7.0 7.0% Si

[0135] The figure also includes two reference alloys: alloy AlSi10Mg (ENAC - 43000), as it represents an alloy that is not prone to cracking; and alloy AlZn5.5MgCu (AA7075), as it is a precipitation - hardenable alloy that is prone to hot cracking. Finally, the composition of the designed alloy was also calculated, but without Si (0% Si). As can be seen, the alloy with 0% Si exhibits a solidification curve similar to that of the alloy prone to hot cracking, with a sharp inflection in the final stage of solidification. However, it does show a significant improvement compared to AlZn5.5MgCu.

[0136] As can be observed, the influence of Si causes the curve to gradually flatten, except for a shift back towards the solid fraction closer to that of alloy AlSi10Mg. Additionally, when incorporating more than 2.4% Si, the solidus temperature decreases, which improves the fluidity of the material during solidification.

[0137] Example 4: Critical solidification range

[0138] A more specific and complementary method for quantifying the susceptibility to hot cracking of aluminum alloys is to represent the figure as a function of temperature and the square root of the solid fraction within a certain range called the critical solidification range. In Figure 7 the slope of the alloy articles of the present invention has been quantified. A smaller slope indicates a lower susceptibility to hot cracking.

[0139] For this purpose, the susceptibility of the alloy to hot cracking can be evaluated by the susceptibility index during the final stage of solidification of the alloy [Kou, S., Acta Mater. 2015, 88, 366 - 374]:

[0140] When is close to 1,

[0141] More specifically, when f s is between 0.87 and 0.94, in other words when is between 0.933 and 0.970, the critical solidification range is defined.

[0142] Therefore, the largest slope (and thus the highest hot - cracking tendency) is maintained by alloy AlZn5.5MgCu, followed by alloy 0% Si (AlZn4.9Cu1.8Mg2.1), and finally alloys 2.4% Si, 3.9% Si, and 7.0% Si with similar susceptibilities. The representative points of the solidification curves according to the criteria used for designing the alloys are summarized in Table 5. As can be seen, the solidification range of the alloy articles of the present invention has been reduced to one - third compared to the solidification range of the alloy used as the reference alloy prone to cracking.

[0143] Table 5. Representative Points of Solidification Curves

[0144]

[0145] Example 5: Microstructure of the alloy according to the present invention processed by computational digital image analysis technology

[0146] For example, Figure 5 The microstructure of an alloy with 7.03% Si processed by digital image analysis technique is shown. The surface of the α-Al matrix (which represents at least 75% in the present invention) is observed in light gray. The interdendritic regions composed of eutectic compounds (which are at most 25% in the alloys of the present invention) are observed in black.

Claims

1. An aluminum alloy, characterized in that, The aluminum alloy comprises: - Zinc in an amount of 4.4 wt% to 5.3 wt%, - Copper in an amount of 1.7 wt% to 1.9 wt%, - Magnesium in an amount of 1.5 wt% to 2.1 wt%, - Silicon in an amount of 2 wt% to 12 wt%, - Optionally, boron in an amount of 0.003 wt% to 1.0 wt%, - Optionally, titanium in an amount of 0.08 wt% to 0.3 wt%, - Optionally, manganese in an amount of 0.1 wt% to 0.4 wt%, - Optionally, chromium in an amount of 0.1 wt% to 0.3 wt%, - Optionally, silver in an amount up to 1.0 wt%, - Optionally, nickel in an amount of 0.01 wt% to 0.02 wt%, - Optionally, zirconium in an amount up to 0.01%, and - Aluminum to balance to 100 wt%.

2. The aluminum alloy according to claim 1, characterized in that, The aluminum alloy comprises boron in an amount of 0.003 wt% to 0.05 wt%, preferably 0.003 wt% to 0.01 wt%.

3. The aluminum alloy according to any one of claims 1 and 2, characterized in that, The aluminum alloy comprises titanium in an amount of 0.08 wt% to 0.2 wt%.

4. The aluminum alloy according to any one of claims 1 to 3, characterized in that The aluminum alloy comprises manganese in an amount of 0.3 wt% to 0.4 wt%.

5. The aluminum alloy according to any one of claims 1 to 4, characterized in that, The aluminum alloy comprises chromium in an amount of 0.2 wt% to 0.3 wt%.

6. The aluminum alloy according to any one of claims 1 to 5, characterized in that, The aluminum alloy comprises nickel in an amount of 0.01 wt% to 0.015 wt%.

7. The aluminum alloy according to any one of claims 1 to 6, characterized in that, The aluminum alloy comprises: 4.9 wt% of zinc, 1.8 wt% of copper, 2.1 wt% of magnesium, Silicon in an amount of 2 wt% to 12 wt%.

8. The aluminum alloy according to any one of claims 1 to 7, characterized in that, The aluminum alloy comprises silicon in an amount of 2.0 wt% to 7 wt%.

9. The aluminum alloy according to any one of claims 1 to 8, characterized in that, The aluminum alloy comprises silicon in an amount of 2.0 wt% to 2.4 wt%.

10. The aluminum alloy according to any one of claims 1 to 8, characterized in that, The aluminum alloy comprises silicon in an amount of 3.5 wt% to 7 wt%, preferably 3.9 wt% to 7 wt%.

11. The aluminum alloy according to any one of claims 1 to 7, characterized in that, The aluminum alloy comprises silicon in an amount of 3.5 wt% to 7 wt%, preferably 3.9 wt% to 7 wt%.

12. The aluminum alloy according to any one of claims 1 to 10, characterized in that, The aluminum alloy comprises silicon in an amount of 10.5 wt% to 12 wt%, preferably 10.5 wt% to 11.2 wt%.

13. Use of the aluminum alloy according to any one of claims 1 to 12 for the preparation of an article by a near-net shape forming manufacturing technique.

14. Use of the aluminum alloy according to claim 13, wherein the manufacturing technique that does not require subsequent cutting is selected from additive manufacturing, linear and rotary friction welding, die casting, sand casting, investment casting or injection molding.

15. An article comprising the aluminum alloy according to any one of claims 1 to 12.

16. An article consisting of the aluminum alloy according to any one of claims 1 to 12.

17. The article according to claim 15 or 16, selected from the housings and structures for mobile phones and laptops, engine blocks in automobiles, gearbox housings, vehicle tires, seat frames in vehicles, battery boxes for electric vehicles.

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