Method for synergistically improving strength and plasticity of 7-series high-strength aluminum alloy welded joint

Abstract

The application provides a method for improving the strength and plasticity of a 7-series high-strength aluminum alloy welding joint, which comprises the following steps: firstly, a flexible laser heat source wire filling welding technology is used to realize the accurate regulation of the stability of a molten pool-small hole and the solidification process, and a nano-particle reinforced aluminum alloy composite wire is added to obtain a welding joint with low porosity and composed of uniform fine equiaxed crystals; and then, the welding joint is subjected to solid solution + regression and aging heat treatment to realize the dissolution of coarse eutectic phases (alpha-Al + MgZn2) and the uniform dispersion of nano-scale (eta' phase) precipitates. The tensile strength and elongation of the 7-series high-strength aluminum alloy joint obtained by the above welding and heat treatment method can both reach more than 95% of the base material, so that the strength and plasticity of the 7-series high-strength aluminum alloy welding joint are improved. The application can completely solve the problems of the formation of welding hot cracks, joint softening, high porosity and low dynamic and static load fatigue of the 7-series high-strength aluminum alloy, and greatly widens the application prospect of the 7-series high-strength aluminum alloy welding component.

Description

Technical Field

[0001] This invention belongs to the field of materials engineering technology and relates to a method for improving the mechanical properties of aluminum alloy welded joints. More specifically, it relates to a method for synergistically improving the strength and plasticity of 7-series high-strength aluminum alloy welded joints. Background Technology

[0002] In the fields of aerospace and automobile manufacturing, high-strength low-density aluminum alloys are the preferred materials for achieving lightweighting. Among them, 7-series aluminum alloys (Al-Zn-Mg-Cu alloys) are typical heat-treatable high-strength aluminum alloys with extremely high tensile strength and excellent fatigue strength, and have broad application prospects in major national projects. The poor weldability of 7-series high-strength aluminum alloys, especially fusion welding, has become a bottleneck problem restricting their further promotion and application. Specifically, it manifests as: (1) softening of weld joints: Under the heat influence of the welding heat source, the original nano-precipitated strengthening phases in the base material of heat-treatable aluminum alloys are easily dissolved back, thereby weakening the mechanical properties of the weld joint. [1] (2) Formation of hot cracks in welding: Aluminum alloys have a high coefficient of thermal expansion, and it is difficult to fill the dendrite gaps during the solidification process of traditional fusion welding, making the welded joints extremely prone to hot cracks. [2] Currently, commercially available 4-series or 5-series aluminum alloy welding wires are mainly used. For example, laser welding and TIG welding heat sources are employed, and ER5356 aluminum-magnesium welding wire is used to weld 7-series high-strength aluminum alloys. [3] The tensile strength of the welded joint is 50% to 60% of that of the base material, and the elongation is 45% to 55% of that of the base material.

[0003] Improving the microstructure of the weld joint through weld metallization, combined with appropriate heat treatment, is an effective way to solve the above problems. Patent No. 201910828999.1 provides an aluminum alloy flux-cored welding wire reinforced with micro / nano particles for welding 7075 aluminum alloy. The addition of ceramic particles promotes heterogeneous nucleation, refining the weld grains and increasing tensile strength to 63% of the base metal's tensile strength. However, the precipitation of coarse intergranular eutectic phases in the weld and the re-dissolution of nano-precipitates in the heat-affected zone do not effectively solve the softening problem of the weld joint, resulting in a significant reduction in plasticity and an elongation of less than 50% of the base metal.

[0004] In conclusion, there is an urgent need to develop a method for synergistically improving the strength and plasticity of 7-series high-strength aluminum alloy welded joints, so as to provide advanced welding technology support for expanding the application scenarios of 7-series high-strength aluminum alloy welded components.

[0005] References:

[0006] [1]Zhang K, Chen J, Ma P, et al. Effect of welding thermal cycle on microstructural evolution of Al-Zn-Mg-Cu alloy[J]. Materials Science&Engineering A, 717(2018)85-94.

[0007] [2]M.Holzer,K.Hofmann,V.Mann,et al.Change of hot crackingsusceptibility in welding of high strength aluminum alloy AA 7075[J].PhysicsProcedia,83(2016)463-471.

[0008] [3]Zhang L, Li Summary of the Invention

[0009] To address the bottleneck problem of the inability to synergistically improve the tensile strength and ductility of welded joints in existing 7-series high-strength aluminum alloy welding, this invention proposes a method for synergistically improving the strength and ductility of 7-series high-strength aluminum alloy welded joints. First, a flexible laser welding heat source is selected. This achieves precise energy distribution between the base material and the welding wire, effectively improving the flow stability of the molten pool and reducing defects such as spatter and porosity. The selected nano-ceramic particle-reinforced 7-series aluminum alloy composite welding wire effectively inhibits dendrite growth, transforming the weld grain structure from inhomogeneous coarse columnar and equiaxed crystals to uniform fine equiaxed crystals. Post-weld, a solution-reversion-re-aging heat treatment process is used to dissolve the coarse intergranular eutectic phase in the weld, followed by the uniform precipitation of a nano-scale second phase within the weld and heat-affected zone, solving the joint softening problem. The 7-series high-strength aluminum alloy joints obtained using this synergistic welding and heat treatment method exhibit tensile strength and elongation exceeding 95% of the base material, thus achieving a synergistic improvement in the strength and ductility of the 7-series high-strength aluminum alloy welded joints.

[0010] The technical means employed in this invention are as follows:

[0011] A method for synergistically improving the strength and plasticity of 7-series high-strength aluminum alloy welded joints is proposed, which employs flexible laser heat source filler wire welding technology; selects 7-series high-strength aluminum alloy composite welding wire with a composition similar to that of the 7-series high-strength aluminum alloy base material to be welded and reinforced with nano-ceramic particles; applies solution heat treatment to the 7-series high-strength aluminum alloy welded joint to dissolve the coarse eutectic phase between grains, obtains a supersaturated solid solution after water quenching, and then performs regression and re-aging heat treatment.

[0012] Furthermore, the flexible laser heat source includes a laser-induced arc composite welding heat source with energy density that can be flexibly controlled and a coaxial pulse-continuous dual laser composite welding heat source.

[0013] Furthermore, the aluminum alloy composite welding wire is a 7-series aluminum alloy composite welding wire reinforced with nano-ceramic particles. It uses TiC or TiB2 nano-ceramic particles to reinforce the 7-series aluminum alloy composite welding wire. The TiC or TiB2 nano-ceramic particles are generated in situ in the weld, with a particle mass fraction ranging from 1.0 to 2.0 wt% and a particle size ranging from 400 to 800 nm. The ceramic particles serve as heterogeneous nucleation sites for aluminum alloys during weld solidification, thus refining the weld microstructure.

[0014] Furthermore, the welding process parameter range should meet the following requirements:

[0015] (1) Laser-induced arc filler wire welding:

[0016] The welding speed range is 500–2500 mm / min, the wire feed speed range is 2000–3500 mm / min, the arc current range during non-consumable electrode gas shielded welding is 80–180 A, the electrode height range is 1 mm–3 mm, the laser power range is 400–4000 W, the laser defocusing adjustment range is -2–+2 mm, the laser frequency range is 20–40 Hz, the laser pulse width range is 2.5–3.0 ms, the distance between the laser beam and the arc electrode ranges from 1.0 to 3.0 mm, and the filament spacing ranges from 2.0 to 5.0 mm.

[0017] (2) Coaxial dual-laser filler wire welding:

[0018] Coaxial dual-beam lasers include continuous lasers and pulsed lasers; the power range of continuous lasers is 1000–6000W, and the defocus range is +5–+30mm; the power range of pulsed lasers is 300–1000W, and the defocus range is -3–20mm; the frequency range of pulsed lasers is 40–90Hz; the welding speed range is 500–5000mm / min; the wire feeding speed is 500–3000mm / min; cold wire feeding; and free forming.

[0019] Furthermore, the heat treatment process refers to the following steps: 7-series high-strength aluminum alloy welded joints first undergo solution treatment, followed by water quenching and then re-aging treatment, including the following steps:

[0020] (1) Solution treatment of 7 series high-strength aluminum alloy welded joints, with a temperature range of 470~480℃ and a holding time range of 1.5~3h;

[0021] (2) Perform water-cooling quenching treatment;

[0022] (3) Perform regression and re-aging treatment: First, perform pre-aging treatment with a temperature range of 120-135℃ and a pre-aging time range of 8-10h; then perform high-temperature short-time regression aging treatment with a temperature range of 170-185℃ and a regression aging time range of 3-5h; finally, perform re-aging treatment with a temperature range of 120-135℃ and a re-aging time range of 15-20h.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. Compared with traditional single laser heat sources, the composite heat sources such as laser-induced arc and coaxial dual lasers in this invention have the advantages of a wide welding process window and flexible control of energy density. They can improve the stability of the weld pool-keyhole during the welding process, control the solidification structure and refine the grains, reduce porosity, and achieve good weld formation.

[0025] 2. In the nano-ceramic particle-reinforced composite aluminum alloy welding wire of the present invention, TiC and TiB2 nano-ceramic particles are formed in situ in the weld during the non-equilibrium solidification process of the molten pool, playing a role in heterogeneous nucleation, effectively improving the nucleation rate of fine equiaxed crystals and inhibiting the formation of coarse columnar crystals and equiaxed crystals, thus reducing the tendency to form solidification cracks.

[0026] 3. In the heat treatment process of this invention, the coarse eutectic phase (MgZn2+α-Al) is completely dissolved in the weld joint matrix through solution treatment, and a supersaturated solid solution is obtained after water quenching. Compared with single-stage aging treatment, the regression re-aging treatment makes the precipitation of nano-MgZn2 phase (η` phase) more uniform and dense, which helps to reduce or eliminate the non-precipitated zone, thereby further improving the strength and plasticity of the weld joint. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This invention presents the grain structure, average grain size, and grain boundary distribution of the welded joint in the method for synergistic improvement of strength and plasticity of 7-series high-strength aluminum alloy welded joints.

[0029] Figure 2 This image shows the microstructure of the welded joint before heat treatment in the method for synergistic improvement of strength and plasticity of 7-series high-strength aluminum alloy welded joints according to the present invention. (a)-(c) represent the heat-affected zone, fusion line, and weld center, respectively.

[0030] Figure 3 This image shows the microstructure of the welded joint after regression and re-aging heat treatment in the method for synergistic improvement of strength and plasticity of 7-series high-strength aluminum alloy welded joints of the present invention. (a)-(c) represent the heat-affected zone, fusion line, and weld center, respectively.

[0031] Figure 4 These are the experimental results of the mechanical properties of the base material and the welded joint before heat treatment in the method for synergistic improvement of strength and plasticity of 7-series high-strength aluminum alloy welded joints of the present invention. Among them, (a) is the engineering stress-strain curve, and (b) is the maximum tensile strength and elongation.

[0032] Figure 5 These are the experimental results of the mechanical properties of the base material and the welded joint after re-aging heat treatment in the method for synergistic improvement of strength and plasticity of 7-series high-strength aluminum alloy welded joints of this invention. Among them, (a) is the engineering stress-strain curve, and (b) is the maximum tensile strength and elongation.

[0033] Figure 6 This is a flowchart illustrating the specific process of this invention. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0037] like Figure 6 As shown, this invention discloses a method for synergistically improving the strength and plasticity of 7-series high-strength aluminum alloy welded joints, employing flexible laser heat source filler wire welding technology; selecting a 7-series high-strength aluminum alloy composite welding wire with a composition similar to the base material of the 7-series high-strength aluminum alloy to be welded and reinforced with nano-ceramic particles; using solution heat treatment to dissolve the coarse eutectic phase between grains in the 7-series high-strength aluminum alloy welded joint, obtaining a supersaturated solid solution after water quenching, and then performing a regression and re-aging heat treatment.

[0038] Furthermore, the flexible laser heat source includes a laser-induced arc composite welding heat source with energy density that can be flexibly controlled and a coaxial pulse-continuous dual laser composite welding heat source.

[0039] Furthermore, the aluminum alloy composite welding wire is a 7-series aluminum alloy composite welding wire reinforced with nano-ceramic particles. It uses TiC or TiB2 nano-ceramic particles to reinforce the 7-series aluminum alloy composite welding wire. The TiC or TiB2 nano-ceramic particles are generated in situ in the weld, with a particle mass fraction ranging from 1.0 to 2.0 wt% and a particle size ranging from 400 to 800 nm. The ceramic particles serve as heterogeneous nucleation sites for aluminum alloys during weld solidification, thus refining the weld microstructure.

[0040] Furthermore, the welding process parameter range should meet the following requirements:

[0041] (1) Laser-induced arc filler wire welding:

[0042] The welding speed range is 500–2500 mm / min, the wire feed speed range is 2000–3500 mm / min, the arc current range during non-consumable electrode gas shielded welding is 80–180 A, the electrode height range is 1 mm–3 mm, the laser power range is 400–4000 W, the laser defocusing adjustment range is -2–+2 mm, the laser frequency range is 20–40 Hz, the laser pulse width range is 2.5–3.0 ms, the distance between the laser beam and the arc electrode ranges from 1.0 to 3.0 mm, and the filament spacing ranges from 2.0 to 5.0 mm.

[0043] (2) Coaxial dual-laser filler wire welding:

[0044] Coaxial dual-beam lasers include continuous lasers and pulsed lasers; the power range of continuous lasers is 1000–6000W, and the defocus range is +5–+30mm; the power range of pulsed lasers is 300–1000W, and the defocus range is -3–20mm; the frequency range of pulsed lasers is 40–90Hz; the welding speed range is 500–5000mm / min; the wire feeding speed is 500–3000mm / min; cold wire feeding; and free forming.

[0045] Furthermore, the heat treatment process refers to the following steps: 7-series high-strength aluminum alloy welded joints first undergo solution treatment, followed by water quenching and then re-aging treatment, including the following steps:

[0046] (1) Solution treatment of 7 series high-strength aluminum alloy welded joints, with a temperature range of 470~480℃ and a holding time range of 1.5~3h;

[0047] (2) Perform water-cooling quenching treatment;

[0048] (3) Perform regression and re-aging treatment: First, perform pre-aging treatment at a temperature range of 120–135℃ for a duration of 8–10 hours; then, perform high-temperature short-time regression aging treatment at a temperature range of 170–185℃ for a duration of 3–5 hours; finally, perform re-aging treatment at a temperature range of 120–135℃ for a duration of 15–20 hours.

[0049] Example 1: Coaxial dual laser filler wire welding of 7A52-T6 aluminum alloy plate

[0050] The continuous laser power was 1000W, the continuous laser defocusing distance was +5mm, the pulsed laser average power was 1000W, the pulsed laser defocusing distance was 0mm, the pulsed laser frequency was 60Hz, the welding speed was 1000mm / min, and the wire feed speed was 1200mm / min. Nano-TiB2 ceramic particle-reinforced 7-series aluminum alloy composite welding wire was used. In-situ TiB2 particles with a particle size range of 400nm and a mass fraction of 1wt% were generated in the weld seam. Cold feeding and free shaping were employed. After welding, the joint underwent solution treatment at 470℃ for 1.5h, followed immediately by water quenching. Then, a re-aging treatment was performed: first, pre-aging at 125℃ for 9h; then, high-temperature short-time re-aging at 175℃ for 4h; finally, re-aging at 125℃ for 16h. By adopting the above-mentioned method of synergistic enhancement of strength and plasticity of 7-series aluminum alloys, the ultimate tensile strength of the joint can reach 96% of that of the 7075-T6 base material, and the elongation can reach 98% of that of the 7A52 base material.

[0051] Without adopting the above-mentioned method of synergistic improvement of strength and plasticity of aluminum alloy welded joints, the tensile strength of the welded specimen is only 65% ​​of that of the 7A52-T6 base material, and the elongation after fracture is about 30% of that of the 7A52-T6 base material.

[0052] Example 2: Coaxial dual laser filler wire welding of 7075-T6 aluminum alloy plate

[0053] The continuous laser power was 6000W, with a defocusing depth of +8mm. The average pulsed laser power was 300W, with a defocusing depth of +2mm. The pulsed laser frequency was 70Hz. The welding speed was 1100mm / min, and the wire feed speed was 1300mm / min. Nano-TiB2 ceramic particle-reinforced 7-series aluminum alloy composite welding wire was used. In-situ TiB2 particles with a particle size range of 600nm and a mass fraction of 1.5wt% were generated in the weld. The wire was cold-fed and freely shaped. After welding, the joint underwent solution treatment at 475℃ for 2 hours, followed by immediate water quenching. Then, a re-aging treatment was performed: first, pre-aging at 130℃ for 9 hours; then, high-temperature short-time re-aging at 180℃ for 4.5 hours; and finally, re-aging at 130℃ for 18 hours. By adopting the above-mentioned method of synergistic enhancement of strength and plasticity of 7-series aluminum alloy, the ultimate tensile strength of the joint can reach 97% of that of 7075-T6 base material, and the elongation can reach 98% of that of 7075 base material.

[0054] Example 3: Coaxial dual laser filler wire welding of 7005-T6 aluminum alloy plate

[0055] The continuous laser power was 1800W, with a defocusing depth of +10mm. The average power of the pulsed laser was 700W, with a defocusing depth of +5mm. The pulsed laser frequency was 80Hz. The welding speed was 1200mm / min, and the wire feed speed was 1400mm / min. A 7-series aluminum alloy composite welding wire reinforced with nano-TiB2 ceramic particles was used. In-situ TiB2 particles with a particle size range of 800nm ​​and a mass fraction of 2wt% were generated in the weld. The wire was cold-fed and freely shaped. After welding, the joint underwent solution treatment at 480℃ for 3 hours, followed by immediate water quenching. Then, a re-aging treatment was performed: first, pre-aging at 135℃ for 10 hours; then, high-temperature short-time re-aging at 185℃ for 5 hours; and finally, re-aging at 135℃ for 19 hours. By adopting the above-mentioned method of synergistic enhancement of strength and plasticity of 7-series aluminum alloy, the ultimate tensile strength of the joint can reach 97% of that of 7005-T6 base material, and the elongation can reach 97% of that of 7005 base material.

[0056] Example 4: Pulsed laser-induced arc hybrid welding of 7075-T6 aluminum alloy sheet

[0057] The welding speed was 1050 mm / min, the wire feed speed was 3000 mm / min, the TIG welding current was 165 A, and the welding torch angle was 45°. The average power of the pulsed laser was 500 W, the laser current was 130 A, the pulse width was 2.8 ms, the frequency was 30 Hz, the defocusing amount was 0 mm, the electrode height was 1 mm, the distance between the laser beam and the arc electrode was 1.5 mm, and the wire spacing was 3 mm. Nano-TiC ceramic particle-reinforced 7-series aluminum alloy composite welding wire was used, generating TiC particles with a particle size range of 400 nm and a mass fraction of 1.0 wt% in situ within the weld. Cold wire feeding and free forming were employed. Figure 1 As shown, 7075 aluminum alloy was welded using 7-series aluminum alloy welding wire with nano-TiC additives, resulting in uniform and fine equiaxed grains in the weld with an average size of 6.5 μm. However, from... Figure 2 As can be seen, a clear and continuous grain boundary distribution, i.e., coarse eutectic phase, is observed at the fusion line and weld center. This is the main reason for the deterioration of the mechanical properties of the welded joint. The stress-strain curve and elongation of the welded joint after welding are shown in the figure. Figure 4 As shown, the ultimate tensile strength of the joint is 358 MPa, which is 67% of that of the base material; the elongation is 3.9%, which is 65% of that of the base material.

[0058] After welding, the joint is solution treated at 480℃ for 1 hour, and then immediately water-quenched. Following this, a re-aging treatment is performed: first, a pre-aging treatment at 130℃ for 9 hours; then a high-temperature, short-time re-aging treatment at 175℃ for 4 hours; and finally, a re-aging treatment at 120℃ for 20 hours. Figure 3 As shown, there is no continuous grain boundary distribution in the fusion line and the center region of the weld, there are almost no residual eutectic phases, and only a small amount of impurity phases exist.

[0059] Figure 5 To obtain the stress-strain curve and elongation of the welded joint after heat treatment, the above-mentioned method of synergistic enhancement of strength and plasticity of 7-series aluminum alloy was adopted. The ultimate tensile strength of the welded joint was 550 MPa, which is 98% of that of the base material; the elongation was 11.8%, which is 99% of that of the base material.

[0060] Example 5: Pulsed laser-induced arc hybrid welding of 7A52-T6 aluminum alloy sheet

[0061] The welding speed was 1100 mm / min, the wire feed speed was 3300 mm / min, the TIG welding current was 170 A, and the welding torch angle was 45°. The pulsed laser power was 600 W with an average power of 135 A, a pulse width of 2.8 ms, a frequency of 35 Hz, a defocusing amount of +1 mm, an electrode height of 1.5 mm, a laser beam-arc electrode spacing of 2 mm, and a filament spacing of 4 mm. A 7-series aluminum alloy composite welding wire reinforced with nano-TiC ceramic particles was used. In-situ TiC particles with a particle size range of 700 nm and a mass fraction of 1.6 wt% were generated in the weld. The wire was cold-fed and freely shaped. After welding, the joint underwent solution treatment at 476℃ for 2 hours, followed by immediate water quenching. Then, a regression and re-aging treatment is performed: first, a pre-aging treatment is conducted at 133℃ for 9 hours; next, a high-temperature short-time regression aging treatment is performed at 183℃ for 4 hours; finally, a re-aging treatment is performed at 135℃ for 19 hours. Using the above method of synergistically improving the strength and ductility of 7-series aluminum alloys, the ultimate tensile strength of the joint can reach 98% of that of the 7A52-T6 base material, and the elongation can reach 98% of that of the 7A52 base material.

[0062] Example 6: Pulsed laser-induced arc hybrid welding of 7005-T6 aluminum alloy sheet

[0063] The welding speed was 900 mm / min, the wire feed speed was 3500 mm / min, the TIG welding current was 174 A, and the welding torch angle was 45°. The pulsed laser power was 800 W with an average power of 140 A, a pulse width of 2.8 ms, a frequency of 40 Hz, a defocusing amount of +2 mm, an electrode height of 2 mm, a laser beam-arc electrode spacing of 2 mm, and a filament spacing of 4 mm. A 7-series aluminum alloy composite welding wire reinforced with nano-TiC ceramic particles was used, generating TiC particles with a particle size range of 800 nm and a mass fraction of 2 wt% in situ within the weld. The wire was cold-fed and freely shaped. After welding, the joint underwent solution treatment at 480℃ for 3 hours, followed immediately by water quenching. Then, a regression and re-aging treatment is performed: first, a pre-aging treatment is conducted at 135℃ for 10 hours; next, a high-temperature short-time regression aging treatment is performed at 185℃ for 5 hours; finally, a re-aging treatment is performed at 135℃ for 20 hours. Using the above method of synergistically improving the strength and ductility of 7-series aluminum alloys, the ultimate tensile strength of the joint can reach 97% of that of the 7005-T6 base material, and the elongation can reach 96% of that of the 7005 base material.

[0064] In summary, this invention employs flexible laser heat source filler wire welding technology to achieve precise control over the stability of the molten pool-keyhole and its solidification process. Combined with the addition of nanoparticle-reinforced aluminum alloy composite welding wire, a welded joint with low porosity and composed of uniform, fine equiaxed crystals is obtained. Then, the welded joint undergoes solution treatment followed by reversion and aging heat treatment to achieve the re-dissolution of coarse eutectic phases (α-Al+MgZn2) and their uniform dispersion and precipitation at the nanoscale (η` phase). The tensile strength and elongation of the 7-series high-strength aluminum alloy joints obtained using the above-mentioned synergistic welding and heat treatment method can reach over 95% of the base material, thus achieving a synergistic improvement in the strength and plasticity of 7-series high-strength aluminum alloy welded joints. This invention can completely solve the problems of hot crack formation, joint softening, high porosity, and low dynamic and static loads such as fatigue in 7-series high-strength aluminum alloy welding, greatly broadening the application prospects of 7-series high-strength aluminum alloy welded components.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synergistically improving the strength and plasticity of 7-series high-strength aluminum alloy welded joints, characterized in that, The flexible laser heat source filler wire welding technology is adopted; the flexible laser heat source includes a laser-induced arc composite welding heat source with energy density that can be flexibly adjusted and a coaxial pulse-continuous dual laser composite welding heat source; A composite welding wire of 7-series high-strength aluminum alloy, with a composition similar to that of the base material of the 7-series high-strength aluminum alloy to be welded and reinforced with nano-ceramic particles, was selected. Among them, TiC or TiB2 nano-ceramic particles were generated in situ in the weld, with a particle mass fraction ranging from 1.0 to 2.0 wt% and a particle size ranging from 400 to 800 nm. The ceramic particles served as heterogeneous nucleation sites for aluminum alloy during the solidification process of the weld, thus refining the weld microstructure. For the 7-series high-strength aluminum alloy welded joints, solution heat treatment is used to dissolve the coarse intergranular eutectic phase, followed by water quenching to obtain a supersaturated solid solution, and then re-aging heat treatment is performed. The heat treatment process refers to the following steps: the 7-series high-strength aluminum alloy welded joint first undergoes solution treatment, followed by water quenching and then re-aging treatment, including the following steps: (1) Solution treatment of 7 series high-strength aluminum alloy welded joints, with a temperature range of 470~480℃ and a holding time range of 1.5~3h; (2) Perform water quenching treatment; (3) Perform regression and re-aging treatment: First, perform pre-aging treatment with a temperature range of 120~135℃ and a pre-aging time range of 8~10h; then perform high-temperature short-time regression aging treatment with a temperature range of 170~185℃ and a regression aging time range of 3~5h; finally, perform re-aging treatment with a temperature range of 120~135℃ and a re-aging time range of 15~20h.

2. The method for synergistically improving the strength and plasticity of 7-series high-strength aluminum alloy welded joints according to claim 1, characterized in that, The welding process parameters for laser-induced arc filler wire welding meet the following requirements: The welding speed range is 500~2500mm / min, the wire feed speed range is 2000~3500mm / min, the arc current range during non-consumable electrode gas shielded welding is 80~180A, the electrode height range is 1mm~3mm, the laser power range is 400~4000W, the laser defocusing adjustment range is -2~+2mm, the laser frequency range is 20~40Hz, the laser pulse width range is 2.5~3.0ms, the distance between the laser beam and the arc electrode ranges from 1.0~3.0mm, and the filament spacing ranges from 2.0~5.0mm.

3. The method for synergistically improving the strength and plasticity of 7-series high-strength aluminum alloy welded joints according to claim 1, characterized in that, The welding process parameters for coaxial dual-laser filler wire welding meet the following requirements: Coaxial dual-beam lasers include continuous lasers and pulsed lasers; the power range of continuous lasers is 1000~6000W, and the defocus range is +5~+30mm; the power range of pulsed lasers is 300~1000W, and the defocus range is -3~20mm; the frequency range of pulsed lasers is 40~90Hz; the welding speed range is 500~5000mm / min; the wire feeding speed is 500~3000mm / min; cold wire feeding; and free forming.

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