Strong and plasticity collaborative improvement method for 7-series high-strength aluminum alloy welded joint

Abstract

The invention provides a 7-series high-strength aluminum alloy welded joint strength and plasticity collaborative improvement method which comprises the following steps: firstly, adopting a flexible laser heat source wire filling welding technology to realize the stability of a molten pool-small hole and the accurate regulation and control of a solidification process, and combining with the addition of a nano-particle reinforced aluminum alloy composite welding wire to improve the strength and plasticity of a 7-series high-strength aluminum alloy welded joint. A welding joint which is low in porosity and composed of uniform and fine isometric crystals is obtained; and then solid solution + regression re-aging heat treatment is carried out on a welded joint, so that redissolution of a coarse eutectic phase (alpha-Al + MgZn2) is realized, and the coarse eutectic phase (alpha-Al + MgZn2) is uniformly dispersed and separated out in a nanoscale (eta phase). The tensile strength and the elongation of the 7-series high-strength aluminum alloy connector obtained through the welding and heat treatment synergistic method can reach 95% or above of base metal, and therefore synergistic improvement of the strength and plasticity of the 7-series high-strength aluminum alloy welded connector is achieved. The problems of formation of 7-series high-strength aluminum alloy welding hot cracks, joint softening, high porosity, low dynamic and static loads such as fatigue and the like can be thoroughly solved, and the application prospect of 7-series high-strength aluminum alloy welding components is greatly widened.

Description

Technical Field

[0001] The present invention belongs to the field of material engineering technology and relates to a method for improving the mechanical properties of aluminum alloy welded joints. Specifically, it especially relates to a method for synergistically improving the strength and plasticity of 7 series high-strength aluminum alloy welded joints. Background Art

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

[0003] Improving the microstructure of the weld joint by weld metallurgy + appropriate heat treatment process is an effective means to solve the above problems. Patent No. 201910828999.1 provides an aluminum alloy flux-cored wire reinforced with micro-nano particles for welding 7075 aluminum alloy. The addition of ceramic particles promotes heterogeneous nucleation and refines the weld grains to increase the tensile strength to 63% of the tensile strength of the parent material. However, the precipitation of coarse intergranular eutectic phases in the weld and the dissolution of nano-precipitated phases in the heat-affected zone have resulted in the softening problem of the weld joint not being effectively solved, resulting in a significant reduction in plasticity and an elongation of only less than 50% of the parent material.

[0004] In summary, there is an urgent need to develop a method to synergistically improve the strength and plasticity of 7 series high-strength aluminum alloy welded joints to provide advanced welding technology support for broadening 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] In view of the bottleneck problem that the tensile strength and plasticity of the welded joints in the existing 7-series high-strength aluminum alloy welding cannot be synergistically improved, the present invention proposes a method for synergistically improving the strength and plasticity of the welded joints of the 7-series high-strength aluminum alloys. First, a flexible laser welding heat source is selected to effectively improve the flow stability of the molten pool and reduce defects such as spatter and pores on the basis of realizing the precise distribution of heat source energy between the parent material and the welding wire; the selected nano-ceramic particle reinforced 7-series aluminum alloy composite welding wire can effectively inhibit the growth of dendrites to achieve the transformation of the weld grain structure from uneven coarse columnar crystals and equiaxed crystals to uniform fine equiaxed crystals; after welding, a solid solution + regression and aging heat treatment process is used to dissolve the coarse intercrystalline eutectic phase in the weld, and then the nano-scale second phase is uniformly precipitated inside the weld and the heat-affected zone to solve the problem of joint softening. The tensile strength and elongation of the 7-series high-strength aluminum alloy joints obtained by the above-mentioned welding and heat treatment synergistic method can reach more than 95% of the parent material, thereby achieving the synergistic improvement of the strength and plasticity of the 7-series high-strength aluminum alloy welded joints.

[0010] The technical means adopted by the present invention are as follows:

[0011] A method for synergistically improving the strength and plasticity of a 7-series high-strength aluminum alloy welded joint adopts a flexible laser heat source wire-filling welding technology; a 7-series high-strength aluminum alloy composite welding wire with a composition close to that of a 7-series high-strength aluminum alloy parent material to be welded and reinforced with nano-ceramic particles is selected; the 7-series high-strength aluminum alloy welded joint is subjected to solution heat treatment to dissolve back the coarse eutectic phase between grains, a supersaturated solid solution is obtained through water-cooling quenching, and then a regression and aging heat treatment is performed.

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

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

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

[0015] (1) Laser induced arc welding with wire filling:

[0016] The welding speed range is 500-2500mm / min, the wire feeding speed range is 2000-3500mm / min, the arc current range is 80-180A during non-melting electrode gas shielded welding, the electrode height range is 1mm-3mm, the laser power range is 400-4000W, the laser defocus 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 range is 1.0-3.0mm, and the filament spacing range is 2.0-5.0mm.

[0017] (2) Coaxial dual laser welding with wire filling:

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

[0019] Furthermore, the heat treatment process refers to: the 7 series high-strength aluminum alloy welded joint is first subjected to solution treatment, and then subjected to regression and aging treatment after water-cooling quenching, including the following steps:

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

[0021] (2) water cooling quenching treatment;

[0022] (3) Regression and re-aging treatment: first, pre-aging treatment is carried out, the temperature range is 120-135°C, and the pre-aging time range is 8-10h; then, high-temperature short-time regression aging treatment is carried out, the temperature range is 170-185°C, and the regression aging time range is 3-5h; finally, re-aging treatment is carried out, the temperature range is 120-135°C, and the re-aging time range is 15-20h.

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

[0024] 1. Compared with the traditional single laser heat source, the composite heat sources such as laser induced arc and coaxial dual laser in the present invention have the advantages of wide welding process window and flexible energy density control, which can improve the stability of welding molten pool-keyhole during welding, realize the control of solidification structure and refinement of 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, which plays a role of heterogeneous nucleation, effectively improving the nucleation rate of fine equiaxed crystals and inhibiting the formation of coarse columnar crystals and equiaxed crystals, thereby reducing the tendency of solidification cracks to form.

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

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 It shows the grain structure, average grain size and grain boundary distribution of the welded joint in the method for synergistically improving the strength and plasticity of the 7 series high-strength aluminum alloy welded joint of the present invention.

[0029] Figure 2 The microstructure morphology of the welded joint without heat treatment in the method for improving the strength and plasticity of the 7 series high-strength aluminum alloy welded joint of the present invention. (a)-(c) are the heat affected zone, the fusion line and the weld center, respectively.

[0030] Figure 3 The microstructure of the welded joint after the regression and aging heat treatment in the method for improving the strength and plasticity of the 7 series high-strength aluminum alloy welded joint of the present invention. (a)-(c) are the heat affected zone, fusion line and weld center respectively.

[0031] Figure 4 The results of the mechanical properties test of the base material and the welded joint before heat treatment in the method for improving the strength and plasticity of the 7-series high-strength aluminum alloy welded joint of the present invention are shown in Figure 1. (a) is the engineering stress-strain curve, and (b) is the maximum tensile strength and elongation.

[0032] Figure 5 The results of the mechanical properties test of the base material and the welded joint after the regression and aging heat treatment in the method for improving the strength and plasticity of the 7 series high-strength aluminum alloy welded joint of the present invention are shown in Figure 1. (a) is the engineering stress-strain curve, and (b) is the maximum tensile strength and elongation.

[0033] Figure 6 It is a specific flow chart of the present invention. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0037] like Figure 6 As shown, the present invention discloses a method for synergistically improving the strength and plasticity of a 7-series high-strength aluminum alloy welded joint, which adopts a flexible laser heat source wire-filling welding technology; a 7-series high-strength aluminum alloy composite welding wire with a composition close to that of a 7-series high-strength aluminum alloy parent material to be welded and reinforced with nano-ceramic particles is selected; the 7-series high-strength aluminum alloy welded joint is subjected to solution heat treatment to dissolve back the coarse eutectic phase between grains, a supersaturated solid solution is obtained through water-cooling quenching, and then a regression and aging heat treatment is performed.

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

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

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

[0041] (1) Laser induced arc welding with wire filling:

[0042] The welding speed range is 500-2500mm / min, the wire feeding speed range is 2000-3500mm / min, the arc current range is 80-180A during non-melting electrode gas shielded welding, the electrode height range is 1mm-3mm, the laser power range is 400-4000W, the laser defocus 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 range is 1.0-3.0mm, and the filament spacing range is 2.0-5.0mm.

[0043] (2) Coaxial dual laser welding with wire filling:

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

[0045] Furthermore, the heat treatment process refers to: the 7 series high-strength aluminum alloy welded joint is first subjected to solution treatment, and then subjected to regression and aging treatment after water-cooling quenching, including the following steps:

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

[0047] (2) water cooling quenching treatment;

[0048] (3) Regression and re-aging treatment: first, pre-aging treatment is carried out, the temperature range is 120-135℃, and the pre-aging time range is 8-10h; then, high-temperature short-time regression aging treatment is carried out, the temperature range is 170-185℃, and the regression aging time range is 3-5h; finally, re-aging treatment is carried out, the temperature range is 120-135℃, and the re-aging time range is 15-20h

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

[0050] The continuous laser power is 1000W, the continuous laser defocus is +5mm, the pulse laser average power is 1000W, the pulse laser defocus is 0mm, the pulse laser frequency is 60Hz, the welding speed is 1000mm / min, and the wire feeding speed is 1200mm / min. Nano-TiB2 ceramic particles are used to reinforce the 7-series aluminum alloy composite welding wire. The TiB2 particles with a particle size range of 400nm and a mass fraction of 1wt% are generated in situ in the weld. The wire is cold fed and free-formed. After welding, the joint is solution treated at a temperature of 470℃ for 1.5h, and water-cooled quenching is performed immediately after removal. Then, regression and re-aging treatment is performed: first, pre-aging treatment is performed at a temperature of 125℃ for 9h; then, high-temperature short-time regression aging treatment is performed at a temperature of 175℃ for 4h; finally, re-aging treatment is performed at a temperature of 125℃ for 16h. By adopting the above-mentioned method of synergistically improving the strength and plasticity of the 7 series aluminum alloy, the ultimate tensile strength of the joint can reach 96% of the 7075-T6 parent material, and the elongation can reach 98% of the 7A52 parent material.

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

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

[0053] The continuous laser power is 6000W, the continuous laser defocus is +8mm, the pulse laser average power is 300W, the pulse laser defocus is +2mm, the pulse laser frequency is 70Hz, the welding speed is 1100mm / min, and the wire feeding speed is 1300mm / min. Nano-TiB2 ceramic particles are used to reinforce the 7-series aluminum alloy composite welding wire. The TiB2 particles with a particle size range of 600nm and a mass fraction of 1.5wt% are generated in situ in the weld. The wire is cold fed and free-formed. After welding, the joint is solution treated at a temperature of 475℃ for 2h, and water-cooled quenching is performed immediately after removal. Then, regression and re-aging treatment is performed: first, pre-aging treatment is performed at a temperature of 130℃ for 9h; then, high-temperature short-time regression aging treatment is performed at a temperature of 180℃ for 4.5h; finally, re-aging treatment is performed at a temperature of 130℃ for 18h. By adopting the above-mentioned method of synergistically improving the strength and plasticity of 7 series aluminum alloy, the ultimate tensile strength of the joint can reach 97% of the 7075-T6 parent material, and the elongation can reach 98% of the 7075 parent material.

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

[0055] The continuous laser power is 1800W, the continuous laser defocus is +10mm, the pulse laser average power is 700W, the pulse laser defocus is +5mm, the pulse laser frequency is 80Hz, the welding speed is 1200mm / min, and the wire feeding speed is 1400mm / min. Nano-TiB2 ceramic particles are used to reinforce the 7-series aluminum alloy composite welding wire. The TiB2 particles with a particle size range of 800nm ​​and a mass fraction of 2wt% are generated in situ in the weld. The wire is cold fed and free-formed. After welding, the joint is solution treated at a temperature of 480℃ for 3h, and water-cooled quenching is performed immediately after removal. Then, regression and re-aging treatment is performed: first, pre-aging treatment is performed at a temperature of 135℃ for 10h; then, high-temperature short-time regression aging treatment is performed at a temperature of 185℃ for 5h; finally, re-aging treatment is performed at a temperature of 135℃ for 19h. By adopting the above-mentioned method of synergistically improving the strength and plasticity of 7 series aluminum alloy, the ultimate tensile strength of the joint can reach 97% of the 7005-T6 base material, and the elongation can reach 97% of the 7005 base material.

[0056] Example 4 Pulse laser induced arc hybrid welding of 7075-T6 aluminum alloy plate

[0057] The welding speed is 1050mm / min, the wire feeding speed is 3000mm / min, the TIG welding current is 165A, and the welding gun angle is 45°; the average power of the pulsed laser power is 500W, the laser current is 130A, the pulse width is 2.8ms, the frequency is 30Hz, the defocus is 0mm, the electrode height is 1mm, the distance between the laser beam and the arc electrode is 1.5mm, the wire spacing is 3mm, and the nano-TiC ceramic particles are used to enhance the 7 series aluminum alloy composite welding wire. The TiC particles generated in situ in the weld have a particle size range of 400nm and a mass fraction of 1.0wt%. The wire is cold fed and free-formed. Figure 1 As shown in Figure 1, the 7075 aluminum alloy was welded by 7 series aluminum alloy wire with nano-TiC added, and uniform and fine equiaxed grains were obtained in the weld with an average size of 6.5 μm. Figure 2 It can be seen that obvious and continuous grain boundary distribution, i.e., coarse eutectic phase, is observed at the fusion line and the center of the weld, which is the main reason for the deterioration of the mechanical properties of the welded joint. Figure 4 As shown, the ultimate tensile strength of the joint is 358MPa, which is 67% of the parent material; the elongation is 3.9%, which is 65% of the parent material.

[0058] After welding, the joint is subjected to solution treatment at a temperature of 480°C for 1 hour, and then immediately subjected to water cooling and quenching. Then, the joint is subjected to regression and re-aging treatment: first, pre-aging treatment is performed at a temperature of 130°C for 9 hours; then, high-temperature short-time regression aging treatment is performed at a temperature of 175°C for 4 hours; and finally, re-aging treatment is performed at a temperature of 120°C for 20 hours. Figure 3 As shown, there is no continuous grain boundary distribution in the fusion line and the center of the weld, there is almost no residual eutectic phase, and only a small amount of impurity phase.

[0059] Figure 5 In order to obtain the engineering stress-strain curve and elongation of the welded joint after heat treatment, the above-mentioned method of synergistically improving the strength and plasticity of the 7 series aluminum alloy was adopted. The ultimate tensile strength of the welded joint was 550MPa, which was 98% of that of the parent material; the elongation was 11.8%, which was 99% of that of the parent material.

[0060] Example 5 Pulse laser induced arc hybrid welding of 7A52-T6 aluminum alloy plate

[0061] The welding speed is 1100mm / min, the wire feeding speed is 3300mm / min, the TIG welding current is 170A, and the welding gun angle is 45°; the average power of the pulsed laser power is 600W, the laser current is 135A, the pulse width is 2.8ms, the frequency is 35Hz, the defocus is +1mm, the electrode height is 1.5mm, the distance between the laser beam and the arc electrode is 2mm, and the wire spacing is 4mm. The 7 series aluminum alloy composite welding wire is reinforced with nano-TiC ceramic particles. The TiC particles generated in situ in the weld have a particle size range of 700nm and a mass fraction of 1.6wt%. The wire is cold fed and free-formed. After welding, the joint is subjected to solid solution treatment at a temperature of 476℃ and a holding time of 2h. After being taken out, it is immediately water-cooled and quenched. Then the re-aging treatment is carried out: first the pre-aging treatment is carried out at a temperature of 133°C for 9 hours; then the high temperature short-time re-aging treatment is carried out at a temperature of 183°C for 4 hours; finally the re-aging treatment is carried out at a temperature of 135°C for 19 hours. By adopting the above-mentioned method of synergistically improving the strength and plasticity of the 7 series aluminum alloy, the ultimate tensile strength of the joint can reach 98% of the 7A52-T6 parent material, and the elongation can reach 98% of the 7A52 parent material.

[0062] Example 6 Pulse laser induced arc hybrid welding of 7005-T6 aluminum alloy plate

[0063] The welding speed is 900mm / min, the wire feeding speed is 3500mm / min, the TIG welding current is 174A, and the welding gun angle is 45°; the average power of the pulsed laser power is 800W, the laser current is 140A, the pulse width is 2.8ms, the frequency is 40Hz, the defocus is +2mm, the electrode height is 2mm, the distance between the laser beam and the arc electrode is 2mm, and the wire spacing is 4mm. The 7-series aluminum alloy composite welding wire is reinforced with nano-TiC ceramic particles. The TiC particles generated in situ in the weld have a particle size range of 800nm ​​and a mass fraction of 2wt%. The wire is cold fed and free-formed. After welding, the joint is subjected to solid solution treatment at a temperature of 480℃ and a holding time of 3h. After being taken out, it is immediately water-cooled and quenched. Then the re-aging treatment is carried out: first the pre-aging treatment is carried out at a temperature of 135°C for 10 hours; then the high temperature short-time re-aging treatment is carried out at a temperature of 185°C for 5 hours; finally the re-aging treatment is carried out at a temperature of 135°C for 20 hours. By adopting the above-mentioned method of synergistically improving the strength and plasticity of the 7 series aluminum alloy, the ultimate tensile strength of the joint can reach 97% of the 7005-T6 parent material, and the elongation can reach 96% of the 7005 parent material.

[0064] In summary, the present invention adopts flexible laser heat source wire-filling welding technology to achieve precise control of the stability of the molten pool-keyhole and its solidification process, and combines the addition of nanoparticles to enhance the aluminum alloy composite welding wire to obtain a welded joint with low porosity and uniform fine equiaxed crystals; then the welded joint is subjected to solid solution + regression and re-aging heat treatment to achieve the dissolution of the coarse eutectic phase (α-Al+MgZn2) and uniform dispersion and precipitation at the nanoscale (η` phase). The tensile strength and elongation of the 7-series high-strength aluminum alloy joint obtained by the above-mentioned welding and heat treatment synergistic method can reach more than 95% of the parent material, thereby achieving the synergistic improvement of the strength and plasticity of the 7-series high-strength aluminum alloy welded joint. The present invention can completely solve the problems of the formation of hot cracks in the welding of the 7-series high-strength aluminum alloy, joint softening, high porosity, and low dynamic and static loads such as fatigue, and will greatly broaden 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, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 improving the strength and plasticity of a 7-series high-strength aluminum alloy welded joint, characterized in that: Flexible laser heat source wire filling welding technology is adopted; 7 series high-strength aluminum alloy composite welding wire with a composition close to that of the 7 series high-strength aluminum alloy base material to be welded and reinforced with nano-ceramic particles is selected; the 7 series high-strength aluminum alloy welded joint is subjected to solid solution heat treatment to dissolve the coarse eutectic phase between grains, and a supersaturated solid solution is obtained through water cooling and quenching, and then regression and aging heat treatment is performed.

2. The method for improving the strength and plasticity of a 7-series high-strength aluminum alloy welded joint according to claim 1, characterized in that: 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.

3. The method for improving the strength and plasticity of a 7-series high-strength aluminum alloy welded joint according to claim 1, characterized in that: The aluminum alloy composite welding wire is a 7 series aluminum alloy composite welding wire reinforced with nano-ceramic particles, wherein TiC or TiB2 nano-ceramic particles are generated in situ in the weld, the particle mass fraction ranges from 1.0 to 2.0 wt%, and the particle size ranges from 400 to 800 nm. The ceramic particles serve as heterogeneous nucleation sites for the aluminum alloy during weld solidification, thereby refining the weld structure.

4. The method for improving the strength and plasticity of a 7-series high-strength aluminum alloy welded joint according to claim 1, characterized in that: The welding process parameter range of laser induced arc wire welding meets the following requirements: The welding speed range is 500-2500mm / min, the wire feeding speed range is 2000-3500mm / min, the arc current range is 80-180A during non-melting electrode gas shielded welding, the electrode height range is 1mm-3mm, the laser power range is 400-4000W, the laser defocus 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 range is 1.0-3.0mm, and the filament spacing range is 2.0-5.0mm.

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

6. The method for synergistically improving strength and plasticity of 7 series high-strength aluminum alloy welded joints according to claim 1, characterized in that: The heat treatment process is as follows: the 7 series high-strength aluminum alloy welded joint is first subjected to solution treatment, and then subjected to regression and aging treatment after water-cooling quenching, including the following steps: (1) Solution treatment of 7 series high-strength aluminum alloy welded joints, the temperature range is 470-480℃, and the holding time range is 1.5-3h; (2) water cooling quenching treatment; (3) Regression and re-aging treatment: first, pre-aging treatment is carried out, the temperature range is 120-135°C, and the pre-aging time range is 8-10h; then, high-temperature short-time regression aging treatment is carried out, the temperature range is 170-185°C, and the regression aging time range is 3-5h; finally, re-aging treatment is carried out, the temperature range is 120-135°C, and the re-aging time range is 15-20h.

Images