Method for improving weld strength and corrosion resistance of 6XXX series aluminum alloy

Abstract

The invention relates to a method for improving the strength and corrosion resistance of a 6XXX series aluminum alloy weld joint, and belongs to the technical field of welding. The method comprises the following steps that S1, the components of a 6XXX series aluminum alloy base material are measured, and the component interval of a filling material is determined according to the components of the base material and the components of an ideal welding seam; the content of Ti in an ideal welding seam is 0.3 wt%-0.6 wt%, the content of Mg is 1.75 wt%-3.05 wt%, and the mass ratio of Mg to Si is (1.8-3.2): 1; s2, the form of a filling material is determined according to the welding form, and the filling material is prepared; and S3, the 6XXX series aluminum alloy base metal is welded through a filling material. By regulating and controlling the contents of elements such as Ti and Mg in the weld joint and optimizing the welding process, the strength and corrosion resistance of the weld joint are synergistically improved under various strengthening systems, so that the welding and manufacturing requirements of light-weight structures in the fields of automobiles, ships, high-speed trains and the like are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a method for improving the strength and corrosion resistance of 6XXX series aluminum alloy welds. Background Art

[0002] Lightweighting is an important means to achieve energy conservation and emission reduction in the transportation industry, and the use of lightweight materials is an important part of lightweighting. 6XXX series aluminum alloys (such as 6061, 6082, 6D10, etc.) have become important lightweight materials due to their advantages of light weight, high specific strength, and easy processing, and are widely used in fields such as automobiles, ships, and high-speed trains. Welding technology is an important way to connect aluminum alloy structural parts. However, aluminum alloys also have characteristics such as high thermal conductivity, fast solidification rate, high laser reflectivity, and large differences in hydrogen solubility between solid and liquid phases. During the welding process, phenomena such as weld grain coarsening and dissolution of nanoscale strengthening phases will occur, resulting in weld softening and porosity defects, seriously damaging the quality of welded joints. In addition, the introduction of heterogeneous microstructures and compositions during welding changes the corrosion resistance of the alloy, and the weld is often more prone to corrosion cracking than the base metal, reducing the service life of the joint.

[0003] In the prior art, the strength of welds is mainly improved by optimizing welding processes, weld microalloying, and heat treatment, etc. Patent CN117620517A refines the weld grains and the size of Fe-rich phases through rare earth element Y, improving the mechanical properties of the weld; Patent CN104827200A adds Sc element to the traditional 4047 welding wire, increasing the tensile strength of the weld by 50 MPa; Patent CN119020644A enables the welding coefficient to exceed 0.8 through post-weld heat treatment and Er element modification; Patent CN117512481A improves the tensile strength of the weld through post-weld heat treatment and simultaneously reduces the exfoliation corrosion grade of the weld.

[0004] It can be found that the commonly used alloying elements at present are mainly rare earth elements such as Sc, Er, and Y, which are relatively expensive, while the research on low-cost alloying elements is less. At the same time, in industrial production, large devices often lack corresponding heat treatment equipment and it is difficult to carry out heat treatment operations on their welds. In addition, due to the presence of Cu element, while the strength of 6XXX series aluminum alloys is improved, their corrosion resistance is relatively poor. Therefore, there is an urgent need for a filler material and method that can synergistically improve the strength and corrosion resistance of 6XXX series aluminum alloy welds, and only through welding, improve the strength of the weld while taking into account its corrosion resistance. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problems of low strength and poor corrosion resistance of 6XXX series aluminum alloy welds in the prior art.

[0006] To solve the above technical problems, the present invention provides a method for improving the strength and corrosion resistance of 6XXX series aluminum alloy welds. Under the condition of ensuring a small number of weld defects, by regulating the contents of elements such as Ti and Mg in the weld and optimizing the welding process, the strength and corrosion resistance of the weld are synergistically improved under various strengthening systems to meet the welding manufacturing requirements of lightweight structures in fields such as automobiles, ships, and high-speed trains.

[0007] The object of the present invention is to provide a method for improving the strength and corrosion resistance of 6XXX series aluminum alloy welds, including the following steps: S1. Determine the composition of the 6XXX series aluminum alloy base material, and determine the composition range of the filler material according to the composition of the base material and the composition of the ideal weld; the Ti content in the ideal weld is 0.3 wt%-0.6 wt%, the Mg content is 1.75 wt%-3.05 wt%, and the mass ratio of Mg to Si is (1.8 - 3.2):1; S2. Determine the form of the filler material according to the welding form and prepare the filler material; S3. Weld the 6XXX series aluminum alloy base material with the filler material.

[0008] In an embodiment of the present invention, in S1, the ideal weld refines the grain size by controlling the Ti content; by controlling the Mg content, the generation of harmful phases is reduced, the formation of beneficial phases is stabilized, electrochemical corrosion is reduced, and the strength and toughness of the weld are improved; when the Mg content is low, free eutectic Si exists in the weld, and anodic dissolution occurs in the precipitate-free zone near it. At the same time, the presence of Si accelerates the polarity conversion between the Mg2Si phase and the matrix; when the Mg content is high, Al3Mg2 phase and S phase are generated at the grain boundaries, and the electrode potentials of these phases are much lower than that of the Al matrix, and anodic dissolution is extremely likely to occur. By controlling the Mg / Si ratio, the contents and morphologies of phases such as eutectic Si, Mg2Si, AlSiCuMg, AlCuMg, and Al3Mg2 in the weld are changed, and their electrochemical corrosion with the matrix is inhibited; only under this condition can it be ensured that the S phase, Al3Mg2 phase, and eutectic Si phase in the weld are relatively few, thereby achieving the improvement of corrosion resistance.

[0009] In an embodiment of the present invention, in S1, the composition of the filler material is calculated according to the following formula: Composition of the filler material = (Composition of the ideal weld - Composition of the 6XXX series aluminum alloy base material × Fusion ratio) / (1 - Fusion ratio); When the form of the filler material is foil or sheet, the fusion ratio = (Weld area - Cross-sectional area of the filler material) / Weld area; When the form of the filler material is welding wire, the fusion ratio = (Weld area - Area of the upper and lower reinforcement) / Weld area.

[0010] Among them, the weld area is the weld area obtained after welding without adding filler material. When the form of the filler material is foil or sheet, the length is equal to the weld length, the width is less than 200 μm, the height is less than the thickness of the 6XXX series aluminum alloy base material, and the cross-sectional area = width × height.

[0011] In an embodiment of the present invention, in S2, the welding form is selected from arc welding and / or laser welding.

[0012] In an embodiment of the present invention, in S2, the form of the filler material is selected from Al-Ti-Mg sheets and / or Al-Mg-Si-Cu-Ti welding wires.

[0013] In an embodiment of the present invention, the elemental composition and mass percentage of the Al-Mg-Si-Cu-Ti welding wire are: Mg 4.6 wt%-6.1 wt%, Si 0.7 wt%-1.0 wt%, Cu 0.4 wt%-0.5 wt%, Ti 0.6 wt%-1.6 wt%, Mn 0.5 wt%-0.6 wt%, Cr 0.2 wt%-0.3 wt%, Fe 0-0.15 wt%, Zn 0-0.1 wt%, and the balance is Al and other inevitable impurities.

[0014] In an embodiment of the present invention, in S3, the welding heat input should be reduced within the range of weld penetration during welding. When arc welding is selected, a large welding current and a fast welding speed should be selected; when laser welding is selected, a high laser power and a fast welding speed should be selected. When the welding form is laser welding, the process parameters of the laser welding are: the welding power is 2100 W-2700 W, the welding speed is 33 mm / s-50 mm / s, the shielding gas is argon, the gas flow rate is 10 L / min-25 L / min, the gas gun angle is 20°, the swing trajectory is circular, the swing frequency is 100 Hz-150 Hz, and the swing amplitude is 1.0 mm-1.6 mm; under this condition, the welding heat input can be controlled to ensure that the filler material and the 6XXX series aluminum alloy base material are fully mixed to reduce the softening degree of the heat affected zone and reduce the porosity.

[0015] In an embodiment of the present invention, the tensile strength of the 6XXX series aluminum alloy weld is 280 MPa-350 MPa, the yield strength is 203 MPa-237 MPa, the microhardness is 84 HV-109 HV, and the corrosion current density is 0.55 μA / cm 2 -1.85 μA / cm 2 , and the welding coefficient is 68.0%-85.0%.

[0016] In an embodiment of the present invention, the porosity of the 6XXX series aluminum alloy weld is less than 1%.

[0017] In one embodiment of the present invention, the metallographic structure of the 6XXX series aluminum alloy weld is equiaxed crystal, and the grain size is 10μm - 30μm.

[0018] In one embodiment of the present invention, the precipitated phases of the 6XXX series aluminum alloy weld are selected from one or more of eutectic Si phase, Al3Ti phase, Mg2Si phase, Q phase (AlSiCuMg), and S phase (AlCuMg).

[0019] The technical solution of the present invention has the following advantages compared with the prior art: (1) By designing the contents of Ti and Mg elements in the filler material, the contents of Ti and Mg elements in the 6XXX series aluminum alloy weld meet certain conditions, so as to achieve the coordinated improvement of the strength and corrosion resistance of the weld. In particular, the tensile strength breaks through 300MPa.

[0020] (2) By optimizing the welding process, the Ti and Mg elements in the filler material react with the 6XXX series aluminum alloy base material to generate precipitated phases such as Al3Ti phase, Mg2Si phase, Q phase, and S phase. The Ti element promotes the refinement of weld grains through heterogeneous nucleation; the Mg element solid-solves into the matrix during the rapid cooling after welding. The combined action of fine grain strengthening and solid solution strengthening improves the mechanical properties of the weld.

[0021] (3) The method of the present invention realizes the coordinated improvement of the weld strength and corrosion resistance, without the need for subsequent heat treatment operations, shortens the process flow, and improves the production efficiency. At the same time, the materials used in the present invention have a lower price, reducing the production cost. Description of the Drawings

[0022] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to the specific embodiments of the present invention in combination with the drawings, where: Figure 1 It is the grain size diagram of the weld in Test Example 1 of the present invention; Figure 2 It is the SEM diagram of the weld in Test Example 2 of the present invention; Figure 3 It is the XRD diagram of the weld in Test Example 2 of the present invention; Figure 4 It is the mechanical property diagram of the weld in Test Example 3 of the present invention; Figure 5 It is the corrosion resistance diagram of the weld in Test Example 3 of the present invention. Detailed Embodiments

[0023] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0024] In the present invention, unless otherwise specified, the reference standard for welding used in the embodiments of the present invention is HG / T 20222-2017.

[0025] In the present invention, unless otherwise specified, the 6XXX series aluminum alloy base material used in the embodiments of the present invention is a T6 state Al-Mg-Si-Cu alloy with dimensions of 100 mm × 60 mm × 2.5 mm; the elemental composition and its mass percentage are as follows: Mg 0.81%, Si 0.97%, Cu 0.43%, Mn 0.50%, Cr 0.23%, Ti 0.03%, and the balance is Al and other inevitable impurities; the heat treatment process is: solution treatment at 560 °C for 1 h first, and then aging at 180 °C for 6 h; the relevant properties are: tensile strength of 408 MPa, yield strength of 385 MPa, and microhardness of 130 HV.

[0026] In the present invention, unless otherwise specified, the determination of the weld area involved in the embodiments of the present invention includes the following steps: mechanically polish the surface of the 6XXX series aluminum alloy base material to remove the surface oxide layer, clean it with alcohol and then dry it; use a swinging laser as the heat source to weld the 6XXX series aluminum alloy base material, the welding form is butt welding, the welding power is 2700 W, the welding speed is 50 mm / s, the shielding gas is pure argon, the shielding gas flow rate is 20 L / min, the gas gun angle is 20°, the swinging trajectory is circular, the swinging frequency is 150 Hz, and the swinging amplitude is 1.6 mm; use wire cutting to cut a 5 mm × 30 mm × 2.5 mm specimen perpendicular to the weld, polish the welded joint successively with 180#, 600#, 1000#, 2000#, 3000# and 5000# water sandpapers, take the macroscopic morphology of the welded joint with a stereomicroscope, and measure the weld area to be 6.58 mm 2 。

[0027] Example 1

[0028] The method for improving the weld strength and corrosion resistance of the 6XXX series aluminum alloy in this embodiment specifically includes the following steps: S1. Determine the composition of the filler material according to the composition of the base material and the composition of the ideal weld; among them, the Ti content in the ideal weld is 0.3 wt%, the Mg content is 1.75 wt%, and the mass ratio of Mg to Si is 1.8:1; The composition of the filler material is calculated according to the following formula: The length of the filler material is the same as that of the weld seam, which is 100 mm; the width is 0.1 mm; the height is the thickness of the 6XXX series aluminum alloy base material, which is 2.5 mm; its cross-sectional area = width × height = 0.1 mm × 2.5 mm = 0.25 mm 2 ; The fusion ratio = (weld area - filler material cross-sectional area) / weld area = (6.58 mm 2 - 0.25 mm 2 ) / 6.58 mm 2 = 0.96; The composition of the filler material = (composition of the ideal weld - composition of the 6XXX series aluminum alloy base material × fusion ratio) / (1 - fusion ratio); the results show that the Ti content in the filler material is 6.78 wt%, the Mg content is 24.31 wt%, and the balance is Al and other inevitable impurities.

[0029] S2. Determine the form of the filler material as a thin sheet according to the welding form of laser welding, and proportion the ingredients according to the composition of the filler material. The raw materials are 99.99% pure Al, Al-10Ti, and 99.9% pure Mg; then obtain the Al-Ti-Mg alloy by gravity casting; then take a 100 mm × 2.5 mm × 0.2 mm Al-Ti-Mg thin sheet from the Al-Ti-Mg alloy by wire cutting, and polish it with 180# sandpaper to remove the wire cutting marks. After polishing to 0.1 mm, clean it with alcohol and blow it dry; S3. Weld the 6XXX series aluminum alloy base material with the filler material, use the oscillating laser as the heat source, the welding power is 2700 W, the welding speed is 50 mm / s, the shielding gas is pure argon, the shielding gas flow rate is 20 L / min, the gas gun angle is 20°, the oscillation trajectory is circular, the oscillation frequency is 150 Hz, and the oscillation amplitude is 1.6 mm.

[0030] Example 2

[0031] Basically the same as Example 1, the differences are as follows: In S1, the Ti content in the ideal weld is 0.6 wt%, the Mg content is 3.05 wt%, and the mass ratio of Mg and Si is 3.2:1; The composition of the filler material is calculated according to the following formula: The width of the filler material is 0.2 mm, the height is 2.5 mm, the length is 100 mm, and its cross-sectional area is 0.5 mm 2 ; calculate the fusion ratio to be 0.92, the Ti content in the filler material is 7.16 wt%, the Mg content is 28.81 wt%, and the balance is Al and other inevitable impurities; In S2, a 100 mm×2.5 mm×0.3 mm Al-Ti-Mg thin sheet was taken from the middle of the Al-Ti-Mg alloy by wire cutting, and it was polished with 180# sandpaper to remove the wire cutting marks. After polishing to 0.2 mm, it was cleaned with alcohol and dried.

[0032] Comparative Example 1

[0033] Basically the same as Example 2, the difference is that: no filler material is used.

[0034] Comparative Example 2

[0035] Basically the same as Example 2, the differences are as follows: The Ti content in the ideal weld is 0.6 wt%, and the Mg content is 0.81 wt% (that is, no additional Mg is added); The composition of the filler material is calculated according to the following formula: The width of the filler material is 0.2 mm, the height is 2.5 mm, the length is 100 mm, and its cross-sectional area is 0.5 mm 2 ; The calculated dilution ratio is 0.92, the Ti content in the filler material is 7.16 wt%, and the balance is Al and other inevitable impurities.

[0036] Comparative Example 3

[0037] Basically the same as Example 2, the differences are as follows: The Ti content in the ideal weld is 0.6 wt%, and the Mg content is 3.5 wt% (that is, excessive Mg is added); The composition of the filler material is calculated according to the following formula: The width of the filler material is 0.2 mm, the height is 2.5 mm, the length is 100 mm, and its cross-sectional area is 0.5 mm 2 ; The calculated dilution ratio is 0.92, the Ti content in the filler material is 7.16 wt%, the Mg content is 34.44 wt%, and the balance is Al and other inevitable impurities.

[0038] Test Example 1

[0039] First, the welds prepared in Example 1 and Comparative Example 1 were electrochemically polished with a 10 vol.% perchloric acid ethanol solution, the electrolysis voltage was 20 V, and the time was 30 s. Then, the crystal structure of the welds was analyzed by electron backscatter diffraction (EBSD), and the results are as Figure 1 shown. From Figure 1It can be seen that the grain size of the weld prepared in Example 1 is about 28.2 μm, and the grain size of the weld prepared in Comparative Example 1 is about 68.7 μm. This is because after Ti modification in Example 1, white Al3Ti phase precipitates in the weld, which serves as heterogeneous nucleation sites for α-Al and significantly refines the weld grains.

[0040] Test Example 2

[0041] First, the microstructures of the welds prepared in Example 1 and Comparative Example 1 were observed by SEM. Then, the precipitated phases of the welds prepared in Examples 1-2 and Comparative Examples 1-3 were qualitatively analyzed by XRD. Finally, the non-equilibrium solidification process of the welds was calculated by Thermo-Calc, and the results are as Figures 2 - 3 shown. From Figures 2 - 3 it can be seen that the precipitated phases of the weld prepared in Example 1 are mainly eutectic Si phase, Al3Ti phase, Mg2Si phase, and Q phase (AlSiCuMg); the precipitated phases of the weld prepared in Example 2 are mainly eutectic Si phase, Al3Ti phase, Mg2Si phase, and S phase (AlCuMg); the precipitated phases of the weld prepared in Comparative Example 1 are mainly eutectic Si phase, Mg2Si phase, and Q phase (AlSiCuMg); the precipitated phases of the weld prepared in Comparative Example 2 are mainly eutectic Si phase, Al3Ti phase, Mg2Si phase, and Q phase (AlSiCuMg); the precipitated phases of the weld prepared in Comparative Example 3 are mainly Al3Ti phase, Mg2Si phase, S phase (AlCuMg), and Al3Mg2 phase. As the Mg content in the weld increases, the eutectic Si phase decreases, and the Q phase gradually transforms into the S phase. When the Mg content further increases, i.e., in Comparative Example 3, Al3Mg2 phase is formed in the weld, and this phase is the anodic phase, which will significantly weaken the corrosion resistance of the weld.

[0042] Test Example 3

[0043] The porosity, strength, etc. of the welds prepared in Examples 1-2 and Comparative Examples 1-3 were tested: (1) Porosity: Samples of 5 mm × 100 mm × 2.5 mm were cut along the weld center by wire cutting, polished by the above method, and their morphologies were photographed by a stereomicroscope. The porosity was calculated according to the area ratio; (2) Tensile strength and yield strength: The tensile strength and yield strength of the welds were tested according to the standard of GB / 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; (3) Microhardness: The microhardness of the welds was tested according to the standard of GB / T4340.1-2009; (4) Welding coefficient: It is the ratio of the tensile strength of the weld to the tensile strength of the base metal; (5) Corrosion current density: The electrochemical corrosion performance of the welded joint was tested using a Princeton versa STAT3 electrochemical workstation. The weld seam was cut separately along the welding direction by wire cutting, and its back was adhered with conductive glue and wires, and then it was embedded with an inlay, and then polished with sandpaper. After immersing the sample in 3.5% NaCl solution for 24 h, electrochemical tests were carried out in the order of open circuit potential, EIS, and Tafel.

[0044] Figures 4 - 5 The relevant properties of the finally measured weld seam are shown in Table 1: Table 1

[0045] From Table 1 and Figures 4 - 5 it can be seen that the method of the embodiment can synergistically improve the mechanical properties and corrosion resistance of the weld seam.

[0046] By comparing Example 2 with Comparative Examples 1-2, it can be seen that when only controlling the Ti element in the weld seam, the mechanical properties and corrosion resistance of the weld seam can also be synergistically improved, but at this time the welding coefficient is only 66.5%, and there is still a large room for improvement in terms of mechanical properties.

[0047] By comparing Example 2 with Comparative Example 3, it can be seen that when the Ti content is in the theoretical range and the Mg element is excessive, the corrosion current density is 3.429 μA / cm 2 , but the corrosion resistance of the weld seam is greatly reduced.

[0048] Obviously, the above embodiments are only examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for improving the strength and corrosion resistance of 6XXX series aluminum alloy welds, characterized in that It includes the following steps: S1. Determine the composition of the 6XXX series aluminum alloy base material, and determine the composition range of the filler material according to the composition of the base material and the composition of the ideal weld. The Ti content in the ideal weld is 0.3wt%-0.6wt%, the Mg content is 1.75wt%-3.05wt%, and the mass ratio of Mg to Si is (1.8-3.2):1; S2. Determine the form of the filler material according to the welding form, and prepare the filler material; S3. Weld the 6XXX series aluminum alloy base material with the filler material.

2. The method for improving the strength and corrosion resistance of the weld of 6XXX series aluminum alloy according to claim 1, characterized in that, In S1, the composition of the filler material is calculated according to the following formula: Composition of the filler material = (Composition of the ideal weld - Composition of the 6XXX series aluminum alloy base material × Fusion ratio) / (1 - Fusion ratio); When the form of the filler material is foil or sheet, the fusion ratio = (Weld area - Cross-sectional area of the filler material) / Weld area; When the form of the filler material is welding wire, the fusion ratio = (Weld area - Area of the upper and lower reinforcement) / Weld area.

3. The method for improving the strength and corrosion resistance of the weld of 6XXX series aluminum alloy according to claim 1, characterized in that In S2, the welding form is selected from arc welding and / or laser welding.

4. The method for improving the strength and corrosion resistance of the weld of 6XXX series aluminum alloy according to claim 1, characterized in that, In S2, the form of the filler material is selected from Al-Ti-Mg sheets and / or Al-Mg-Si-Cu-Ti welding wires.

5. The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloy according to claim 4, characterized in that, The elemental composition and mass percentage of the Al-Mg-Si-Cu-Ti welding wire are: Mg 4.6wt%-6.1wt%, Si 0.7wt%-1.0wt%, Cu 0.4wt%-0.5wt%, Ti 0.6wt%-1.6wt%, Mn 0.5wt%-0.6wt%, Cr 0.2wt%-0.3wt%, Fe 0-0.15wt%, Zn 0-0.1wt%, and the balance is Al and other inevitable impurities.

6. The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloy according to claim 1, characterized in that, In S3, when the welding form is laser welding, the process parameters of the laser welding are: welding power is 2100W-2700W, welding speed is 33mm / s-50mm / s, the shielding gas is argon, the gas flow rate is 10L / min-25L / min, the gas gun angle is 20°, the oscillation trajectory is circular, the oscillation frequency is 100Hz-150Hz, and the oscillation amplitude is 1.0mm-1.6mm.

7. The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloy according to claim 1, characterized in that, The tensile strength of the 6XXX series aluminum alloy weld is 280 MPa - 350 MPa, the yield strength is 203 MPa - 237 MPa, the microhardness is 84 HV - 109 HV, and the corrosion current density is 0.55 μA / cm 2 -1.85 μA / cm 2 , and the welding coefficient is 68.0% - 85.0%.

8. The method for improving the strength and corrosion resistance of the weld of 6XXX series aluminum alloy according to claim 1, characterized in that, The porosity of the 6XXX series aluminum alloy weld is less than 1%.

9. The method for improving the strength and corrosion resistance of the weld seam of 6XXX series aluminum alloy according to claim 1, characterized in that, The metallographic structure of the 6XXX series aluminum alloy weld is fully equiaxed crystal, and the grain size is 10μm-30μm.

10. The method for improving the strength and corrosion resistance of the weld of 6XXX series aluminum alloy according to claim 1, characterized in that, The precipitation phases of the 6XXX series aluminum alloy weld are selected from one or more of eutectic Si phase, Al3Ti phase, Mg2Si phase, Q phase and S phase.

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