A composite welding method for Al-Mg-Si-Cu series aluminum alloy

Abstract

This invention relates to a composite welding method for Al-Mg-Si-Cu aluminum alloys, belonging to the field of welding technology. The composite welding method of this invention includes the following steps: S1, filling nickel foil between the weld seams formed by two workpieces to be welded, determining the relative positions of a galvanometer laser welding machine and a co-pulse CMT welding machine, with the galvanometer laser preceding the heat source; the co-pulse CMT welding machine uses Al-Si welding wire; S2, determining the welding process parameters for the galvanometer laser and the co-pulse CMT; S3, performing welding using the galvanometer laser-co-pulse CMT composite welding process. By improving welding technology, the alloying composition of the weld metal is optimized during the welding stage; and by synergistically utilizing the two heat sources (galvanometer laser and co-pulse CMT) to ensure good weld formation, the heat input to the heat-affected zone of the weld joint is reduced. This significantly improves the strength of the weld joint under the synergistic control of multiple technologies, effectively alleviating the problem of joint softening.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a composite welding method of Al-Mg-Si-Cu series aluminum alloy. Background Art

[0002] In the context of international energy tension, the country has proposed the policies of "carbon peak" and "carbon neutrality" to cope with the energy shortage. At the same time, in this context, higher requirements are put forward for the manufacturing of transportation vehicles, which must not only meet high load-bearing capacity and high-speed operation performance, but also achieve green energy saving. To this end, aluminum is used instead of steel to develop new lightweight transportation vehicles, such as aluminum rail transit vehicles and aluminum car bodies. The requirements for lightweight, sealing and corrosion resistance are higher, making high-strength aluminum alloy bodies widely used.

[0003] However, for high-strength heat-treatable aluminum alloy welding, joint softening is inevitable after welding. Softening is mainly caused by the coarsening of nano-scale precipitation strengthening phases in the weld and heat-affected zone, resulting in softening of the structure; in addition, poor weld forming and excessively high weld porosity reduce the actual bearing area of ​​the joint, which greatly reduces the strength of the joint. Similarly, Al-Mg-Si-Cu series aluminum alloys with high strength and heat-treatable aluminum alloys also face the problem of greatly reduced strength after welding. At present, when commercial welding wires are used to weld Al-Mg-Si-Cu series aluminum alloys with tensile strength exceeding 300MPa, the tensile strength of the joint after welding is generally below 260MPa. If you want to further improve the strength of the weld, post-weld heat treatment is generally used, but this process not only increases the manufacturing cycle, but also increases the manufacturing cost; in addition, post-weld heat treatment will greatly increase the risk of deformation of the welded product, thereby reducing the product qualification. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problem of low strength of Al-Mg-Si-Cu series aluminum alloy welded joints in the prior art.

[0005] In order to solve the above technical problems, the present invention provides a composite welding method of Al-Mg-Si-Cu aluminum alloy, which optimizes the design of weld metal alloying components during the welding stage by improving welding technology; and uses the two heat sources of galvanometer laser-coordinated pulse CMT to reduce the heat input effect on the heat-affected zone of the weld joint under the condition of ensuring good weld formation. The strength of the weld joint is greatly improved under the technology of coordinated regulation of multiple technologies, effectively alleviating the problem of joint softening.

[0006] The object of the present invention is to provide a composite welding method for Al-Mg-Si-Cu aluminum alloy, comprising the following steps:

[0007] S1. Fill nickel foil between the welds formed by two workpieces to be welded, determine the relative positions of the galvanometer laser welding machine and the coordinated pulse CMT welding machine, and the heat source sequence is the galvanometer laser front; the welding wire used by the coordinated pulse CMT welding machine is Al-Si welding wire;

[0008] S2. Determine the welding process parameters of the galvanometer laser and the coordinated pulse CMT: the oscillation trajectory of the galvanometer laser is a circular oscillation trajectory; the pulse current used by the coordinated pulse CMT includes a high-frequency pulse current stage, a low-frequency pulse current stage and a CMT current waveform stage;

[0009] S3. Welding is performed using a galvanometer laser-synergistic pulse CMT hybrid welding process.

[0010] In one embodiment of the present invention, in S1, the thickness of the nickel foil is 35 μm-45 μm, the width of the nickel foil is the same as the depth of the weld, and the length of the nickel foil is the same as the length of the weld.

[0011] In one embodiment of the present invention, in S1, the chemical composition and mass percentage of the nickel foil are: nickel 99.9%-100%, and the remainder is other inevitable impurities.

[0012] In one embodiment of the present invention, in S1, the chemical composition of the Al-Si welding wire and its mass percentage are: silicon 5%-11%, iron 0-0.2%, manganese 0-0.1%, magnesium 0-0.1%, copper 0-0.1%, chromium 0-0.1%, titanium 0-0.1%, and the balance is aluminum and other inevitable impurities.

[0013] In one embodiment of the present invention, in S2, the angle between the laser beam and the welding plane where the workpieces to be welded are located is 80°-85°, and the angle between the laser beam and the welding wire is 35°-40°.

[0014] In one embodiment of the present invention, in S2, the angle between the coordinated pulse CMT welder and the welding plane where the workpiece to be welded is located is 60°-65°, and the wire spacing between the end of the welding wire and the end of the laser beam is 3mm-4mm.

[0015] In one embodiment of the present invention, in S2, the welding process parameters of the galvanometer laser are: an oscillation frequency of 50 Hz-100 Hz, an oscillation amplitude of 0.8 mm-1.6 mm, and a laser power of 1.7 kW-1.9 kW.

[0016] In one embodiment of the present invention, in the entire control current cycle, the high-frequency pulse current stage, the low-frequency pulse current stage and the CMT current waveform stage account for 55%-70%, 25%-35% and 5%-10% respectively.

[0017] In one embodiment of the present invention, in S3, shielding gas is introduced during welding; the shielding gas at the upper part of the weld is delivered by a coordinated pulse CMT welder, and the gas flow rate is 20mL / min-25mL / min; the shielding gas at the lower part of the weld is delivered through the shielding gas duct of the bottom platform, and the gas flow rate is 15mL / min-20mL / min.

[0018] In one embodiment of the present invention, the protective gas is argon gas with a purity of more than 99.99%. The argon gas is used for protection to isolate the surrounding environment of the molten pool.

[0019] The technical solution of the present invention has the following advantages over the prior art:

[0020] (1) The method described in the present invention adopts a galvanometer laser and a coordinated pulse CMT composite welding method, and adds Ni elements (nickel foil) to the Al-Si welding wire to improve the alloying composition of the weld and reduce the softening of the weld structure. In addition, due to the swing characteristics of the galvanometer laser, the flow of the molten pool metal during welding is accelerated, which increases the removal of pores, thereby reducing the porosity of the weld; the galvanometer laser has high-density energy concentration, thereby reducing the impact of thermal softening on the heat-affected zone, thereby enhancing the entire weld joint area. At the same time, the composite coordinated pulse CMT technology enables the technical method to make up for the limitations of a single laser heat source when welding a large assembly gap weld, and improves the application scenario of the technology. Ni (nickel) elements are added to the welding material, and the weld structure softening is reduced by regulating the composition of the Al-Mg-Si-Cu aluminum alloy weld. The combination of multiple technologies increases the strength of the Al-Mg-Si-Cu aluminum alloy weld joint to above 300MPa.

[0021] (2) The method described in the present invention is designed mainly from three aspects: First, for the softening of the weld structure: a galvanometer laser-coordinated pulse CMT composite welding method of high-Ni composite Al-Si welding wire is proposed, and the Ni element forms a large number of mesh-distributed Al in the molten pool. 3Ni intermetallic compounds effectively strengthen the weld by reducing the load on the α-Al matrix. At the same time, the Ni element dissolved in the α-Al matrix further forms a solid solution strengthening on the matrix. Second, inhibit the formation of holes in the weld: the galvanometer laser disturbs the molten pool liquid through a high-energy beam with a circular swing trajectory, improving the fluidity of the molten pool and facilitating the discharge of gas; at the same time, a certain proportion of high-frequency pulse current in the coordinated pulse CMT realizes the improvement of the impact force of the molten droplet on the molten pool, further improving the fluidity of the molten pool and facilitating the discharge of small and dense hydrogen pores in the molten pool. Third, for the softening of the heat-affected zone: the low-frequency pulse current stage in the coordinated pulse CMT realizes the reduction of heat input and reduces the impact on the heat-affected zone of the joint; at the same time, the addition of high-energy laser beams makes the heat input even more reduced under the condition of a certain melting depth. The galvanometer laser + coordinated pulse CMT and high-nickel Al-Si welding wire cooperate in many ways to improve the strength of the Al-Mg-Si-Cu series aluminum alloy welding joints.

[0022] (3) The galvanometer laser in the method described in the present invention has a circular trajectory swing effect, which can promote the flow of molten pool liquid and facilitate gas discharge. The coordinated pulse CMT heat source has a high- and low-frequency pulse current stage coordinated composition. The high-frequency stage enhances the impact force of the molten droplet on the molten pool, enhances the flow of the molten pool and facilitates gas discharge, and the low-frequency stage reduces the heat input and reduces the softening of the heat-affected zone. The galvanometer laser-coordinated pulse CMT composite method can ensure the effective cooperation of the two heat sources and ensure that the respective advantages of the two heat sources can be stably realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0024] Figure 1 It is a structural schematic diagram of the galvanometer laser-cooperative pulse CMT composite welding method of the present invention;

[0025] Figure 2 It is a schematic diagram of the swing trajectory of the galvanometer laser of the present invention;

[0026] Figure 3 It is a schematic diagram of current composition in the high-frequency pulse current stage, the low-frequency pulse current stage and the CMT current waveform stage of the coordinated pulse CMT of the present invention;

[0027] Figure 4 The weld hardness distribution diagram of Example 1 of the present invention and Comparative Example 1;

[0028] Figure 5 The main constituent elements and types of the precipitated phases in the weld of Example 1 of the present invention; wherein (a) is a SEM image of the weld structure and its corresponding EDS analysis element distribution diagram, and (b) is an XRD test result;

[0029] Figure 6 It is a side morphology diagram of the weld fracture of Example 1 of the present invention; wherein a is a macroscopic morphology diagram of the fracture, and b is a locally enlarged microscopic morphology diagram of the position of the dotted box in Figure a.

[0030] Explanation of the reference numerals: 1-galvanometer laser welding machine, 11-laser beam, 2-cooperative pulse CMT welding machine, 21-welding wire, 3-welding plate, 4-nickel foil. DETAILED DESCRIPTION

[0031] The present invention is 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 implement it, but the embodiments are not intended to limit the present invention.

[0032] In the present invention, unless otherwise specified, the chemical composition and mass percentage of the nickel foil used in the embodiments are: 99.99% nickel, and the balance is other inevitable impurities. The width of the nickel foil is the same as the depth of the weld, the length is the same as the length of the weld, and the top and end of the nickel foil are flush with the top surface and section of the welded test plate.

[0033] In the present invention, unless otherwise specified, the chemical composition and mass percentage of the Al-Si welding wire used in the embodiment are: silicon 11%, iron 0.2%, manganese 0-0.1%, magnesium 0-0.1%, copper 0-0.1%, chromium 0-0.1%, titanium 0-0.1%, and the balance is aluminum and other inevitable impurities.

[0034] In the present invention, unless otherwise specified, the purity of argon gas used in the examples is 99.99%.

[0035] Example 1

[0036] Reference Figure 1-3 As shown, the galvanometer laser-coordinated pulse CMT hybrid welding method of the present invention specifically includes the following steps:

[0037] S1. Grind and clean the welding plate 3 with a thickness of 2 mm, and clean the nickel foil 4 with a thickness of 40 μm with alcohol, and then dry it with hot air at a temperature of 55°C; clamp the welding plate 3 on the welding workbench, and clamp the nickel foil 4 between the welds formed by the welding plate 3, determine the relative positions of the galvanometer laser welding machine 1 and the collaborative pulse CMT welding machine 2, and the heat source sequence is the galvanometer laser front; wherein, the welding wire 21 used by the collaborative pulse CMT welding machine 2 is Al-Si welding wire 21.

[0038] S2. Determine the welding process parameters of galvanometer laser and coordinated pulse CMT:

[0039] The angle α between the laser beam 11 and the plane of the welding plate 3 is 80°, which prevents the aluminum alloy from reflecting the laser into the laser and damaging the optical path;

[0040] The angle β between the laser beam 11 and the welding wire 21 is 40°;

[0041] The angle γ between the coordinated pulse CMT welder 2 and the plane of the welding plate 3 is 60°, which ensures that the molten drop formed by the wire feeding at this angle is effectively melted into the weld;

[0042] The wire distance L between the end of the welding wire 21 and the end of the laser beam 11 1 The diameter of the heat source is 3mm, which effectively avoids the interference of the plasma formed around the arc on the laser beam and ensures that the molten pool formed by the galvanometer laser heat source and the molten pool formed by the coordinated pulse CMT heat source can be effectively combined into a whole.

[0043] The galvanometer laser uses a circular swing trajectory, the swing amplitude is the radius of the circular motion trajectory (1.6mm), the swing frequency is the frequency of one circle of the circular trajectory (100Hz), and the laser power is 1.8kW;

[0044] The pulse current of the coordinated pulse CMT welding machine 2 consists of a high-frequency pulse current stage, a low-frequency pulse current stage, and a CMT current waveform stage, and the proportions of the pulse current in the entire control current cycle are 60%, 30%, and 10% respectively.

[0045] S3. In argon atmosphere, welding is performed by galvanometer laser-synergistic pulse CMT composite welding process; the argon gas on the upper part of the weld is transported by the collaborative pulse CMT welder with a gas flow rate of 25 mL / min; the argon gas on the lower part of the weld is transported by the protective gas duct of the bottom platform with a gas flow rate of 20 mL / min; the wire feeding speed is 3 m / min and the welding speed is 50 mm / s.

[0046] Example 2

[0047] The galvanometer laser-coordinated pulse CMT composite welding method of the present invention specifically comprises the following steps:

[0048] S1. Grind and clean the welding plate 3 with a thickness of 2 mm, and clean the nickel foil 4 with a thickness of 35 μm with alcohol, and then dry it with hot air at a temperature of 55°C; clamp the welding plate 3 on the welding workbench, and clamp the nickel foil 4 between the welds formed by the welding plate 3, determine the relative positions of the galvanometer laser welding machine 1 and the collaborative pulse CMT welding machine 2, and the heat source sequence is the galvanometer laser front; wherein, the welding wire 21 used by the collaborative pulse CMT welding machine 2 is Al-Si welding wire 21.

[0049] S2. Determine the welding process parameters of galvanometer laser and coordinated pulse CMT:

[0050] The angle α between the laser beam 11 and the plane of the welding plate 3 is 80°, which prevents the aluminum alloy from reflecting the laser into the laser and damaging the optical path;

[0051] The angle β between the laser beam 11 and the welding wire 21 is 40°;

[0052] The angle γ between the coordinated pulse CMT welder 2 and the plane of the welding plate 3 is 60°, which ensures that the molten drop formed by the wire feeding at this angle is effectively melted into the weld;

[0053] The wire distance L between the end of the welding wire 21 and the end of the laser beam 11 1 The diameter of the heat source is 4mm, which effectively avoids the interference of the plasma formed around the arc on the laser beam and ensures that the molten pool formed by the galvanometer laser heat source and the molten pool formed by the coordinated pulse CMT heat source can be effectively combined into a whole.

[0054] The galvanometer laser uses a circular swing trajectory, the swing amplitude is the radius of the circular motion trajectory (0.8mm), the swing frequency is the frequency of one circle of the circular trajectory (50Hz), and the laser power is 1.8kW;

[0055] The pulse current of the coordinated pulse CMT welding machine 2 consists of a high-frequency pulse current stage, a low-frequency pulse current stage, and a CMT current waveform stage, and the proportions of the pulse current in the entire control current cycle are 70%, 25%, and 5% respectively.

[0056] S3. In argon atmosphere, welding is performed by galvanometer laser-synergistic pulse CMT composite welding process; the argon gas on the upper part of the weld is transported by the collaborative pulse CMT welder with a gas flow rate of 25 mL / min; the argon gas on the lower part of the weld is transported by the protective gas duct of the bottom platform with a gas flow rate of 20 mL / min; the wire feeding speed is 3 m / min and the welding speed is 50 mm / s.

[0057] Comparative Example 1

[0058] S1. Grind and clean the welding plate 3 with a thickness of 2 mm, and then dry it with hot air at a temperature of 55°C; clamp and fix the welding plate 3 on the welding workbench, determine the relative positions of the galvanometer laser welding machine 1 and the collaborative pulse CMT welding machine 2, and the heat source sequence is the galvanometer laser front; wherein, the welding wire 21 used by the collaborative pulse CMT welding machine 2 is Al-Si welding wire 21.

[0059] S2. Determine the welding process parameters of galvanometer laser and coordinated pulse CMT:

[0060] The angle α between the laser beam 11 and the plane of the welding plate 3 is 80°, which prevents the aluminum alloy from reflecting the laser into the laser and damaging the optical path;

[0061] The angle β between the laser beam 11 and the welding wire 21 is 40°;

[0062] The angle γ between the coordinated pulse CMT welder 2 and the plane of the welding plate 3 is 60°, which ensures that the molten drop formed by the wire feeding at this angle is effectively melted into the weld;

[0063] The wire distance L between the end of the welding wire 21 and the end of the laser beam 11 1 The diameter of the heat source is 3mm, which effectively avoids the interference of the plasma formed around the arc on the laser beam and ensures that the molten pool formed by the galvanometer laser heat source and the molten pool formed by the coordinated pulse CMT heat source can be effectively combined into a whole.

[0064] The galvanometer laser uses a circular swing trajectory, the swing amplitude is the radius of the circular motion trajectory (0.4mm), the swing frequency is the frequency of one circle of the circular trajectory (60Hz), and the laser power is 1.8kW;

[0065] The pulse current of the coordinated pulse CMT welding machine 2 consists of a high-frequency pulse current stage, a low-frequency pulse current stage, and a CMT current waveform stage, the proportions of which in the entire control current cycle are 90%, 5%, and 5%, respectively.

[0066] S3. In argon atmosphere, welding is performed by galvanometer laser-synergistic pulse CMT composite welding process; the argon gas on the upper part of the weld is transported by the collaborative pulse CMT welder with a gas flow rate of 25 mL / min; the argon gas on the lower part of the weld is transported by the protective gas duct of the bottom platform with a gas flow rate of 20 mL / min; the wire feeding speed is 3 m / min and the welding speed is 50 mm / s.

[0067] Test Example 1

[0068] The hardness of the welds of Example 1 and Comparative Example 1 was tested using a Vickers hardness tester with a pressure of 1.96 N and a holding time of 10 s. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the weld after nickel alloying in Example 1 (average hardness: 96.2 HV) is 26 HV higher than the weld without nickel alloying in Comparative Example 1 (average hardness: 70 HV), indicating that the hardness of the weld is significantly improved after nickel alloying.

[0069] Test Example 2

[0070] The contents of Ni and other elements in the weld after nickel alloying were calculated based on the weld cross-sectional morphology and weld dilution rate of Example 1, as shown in Table 1.

[0071] Table 1 Element composition of weld metal (mass fraction %)

[0072] Thickness / μm Si Mg Mn Fe Cr Cu Ti Ni Al Nickel Foil 40 3.50 0.64 0.45 0.16 0.19 0.30 0.01 3.60 margin

[0073] Further analysis of the weld structure results Figure 5 As shown. Figure 5 (a) It can be seen that the bright white precipitate phase in the weld is mainly composed of Si, Ni and Al elements, and there is obvious enrichment of Ni element. Figure 5 (b) It can be seen that, combined with the element composition of the precipitate phase and the XRD test results of the weld, after nickel alloying, the newly added bright white precipitate phase in the weld is mainly Al 3 Your phase.

[0074] Table 2 Element composition of weld precipitate phase (mass percentage %).

[0075]

[0076] The microscopic morphology of the weld fracture side is as follows Figure 6 As shown. Figure 6 a It can be seen that the bright white precipitated phase Al 3 The Ni phase bears more load in the elastic stage, and more Al 3 The Ni phase forms microcracks, which effectively strengthens the weld by reducing the load on the α-Al matrix. The microcracks merge with each other to form larger cracks, such as Figure 6 b (dashed circle). At the same time, there are a lot of Al 3 Ni phase. The Ni element dissolved in the α-Al matrix further strengthens the weld through solid solution strengthening, effectively solving the weld softening problem.

[0077] Test Example 3

[0078] The tensile strength test of the welded joints of Examples 1-2 and Comparative Example 1 was performed using a universal electronic testing machine at a tensile speed of 1 mm / min. The results are shown in Table 3:

[0079] Table 3

[0080] Sample Example 1 Example 2 Comparative Example 1 Average tensile strength / MPa 305.3 300.2 248

[0081] It can be seen from Table 3 that the average tensile strength of the welded joint of the embodiment is 300.2 at the lowest, which is significantly higher than the average tensile strength of the comparative example of 248. The excellent tensile strength of the embodiment is because the method of the present invention makes the Al content in the weld microstructure 3 The solid solution of Ni phase and Ni element in the α-Al matrix improves the hardness of the weld structure, so the strength is also improved.

[0082] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled 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 methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A composite welding method for Al-Mg-Si-Cu aluminum alloy, characterized in that: The following steps are included: S1. Fill nickel foil between the welds formed by two workpieces to be welded, determine the relative positions of the galvanometer laser welding machine and the coordinated pulse CMT welding machine, and the heat source sequence is galvanometer laser front; the welding wire used by the coordinated pulse CMT welding machine is Al-Si welding wire; the chemical composition and mass percentage of the Al-Si welding wire are: silicon 5%-11%, iron 0-0.2%, manganese 0-0.1%, magnesium 0-0.1%, copper 0-0.1%, chromium 0-0.1%, titanium 0-0.1%, and the balance is aluminum and other inevitable impurities; S2. Determine the welding process parameters of the galvanometer laser and the coordinated pulse CMT: the oscillation trajectory of the galvanometer laser is a circular oscillation trajectory; the pulse current used by the coordinated pulse CMT includes a high-frequency pulse current stage, a low-frequency pulse current stage and a CMT current waveform stage; the welding process parameters of the galvanometer laser are: an oscillation frequency of 50Hz-100Hz, an oscillation amplitude of 0.8mm-1.6mm, and a laser power of 1.7kW-1.9kW; in the entire control current cycle, the high-frequency pulse current stage, the low-frequency pulse current stage and the CMT current waveform stage account for 55%-70%, 25%-35% and 5%-10% respectively; S3. Welding is performed using a galvanometer laser-synergistic pulse CMT hybrid welding process.

2. The composite welding method of Al-Mg-Si-Cu aluminum alloy according to claim 1, characterized in that: In S1, the thickness of the nickel foil is 35 μm-45 μm.

3. The composite welding method of Al-Mg-Si-Cu aluminum alloy according to claim 1, characterized in that: In S1, the chemical composition and mass percentage of the nickel foil are: nickel 99.9%-100%, and the remainder is other inevitable impurities.

4. The composite welding method of Al-Mg-Si-Cu aluminum alloy according to claim 1, characterized in that: In S2, the angle between the laser beam and the welding plane where the workpieces to be welded are located is 80°-85°, and the angle between the laser beam and the welding wire is 35°-40°.

5. The composite welding method of Al-Mg-Si-Cu aluminum alloy according to claim 1, characterized in that: In S2, the angle between the coordinated pulse CMT welder and the welding plane where the workpiece to be welded is located is 60°-65°, and the wire spacing between the end of the welding wire and the end of the laser beam is 3mm-4mm.

6. The composite welding method of Al-Mg-Si-Cu aluminum alloy according to claim 1, characterized in that: In S3, shielding gas is introduced during welding; the shielding gas at the upper part of the weld is delivered by the coordinated pulse CMT welder, and the gas flow rate is 20mL / min-25mL / min; the shielding gas at the lower part of the weld is delivered through the shielding gas duct of the bottom platform, and the gas flow rate is 15mL / min-20mL / min.

7. The composite welding method of Al-Mg-Si-Cu aluminum alloy according to claim 6, characterized in that: The protective gas is argon gas with a purity of more than 99.99%.

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