A method for improving the strength, toughness and fatigue resistance of aluminum alloy welds

Abstract

The present invention relates to a method for improving the strength, toughness and fatigue resistance of aluminum alloy welds, and belongs to the field of welding technology. The method of the present invention comprises the following steps: S1, using Al-Si-Cu-Mg series welding wire to perform fill welding on aluminum alloy base material, inducing the precipitation of strengthening phase in the weld, and the grains in the weld are cellular grains; S2, laser remelting the weld surface of the fill welding to remelt and solidify the weld surface, on the one hand, releasing pores to reduce the porosity, and making the size of the cellular grains gradiently distributed along the depth direction of the weld; on the other hand, making the atomic solubility gradiently distributed in the depth direction of the weld, so that the number and size of the strengthening phase are gradiently distributed along the depth direction of the weld; by adjusting the fill welding and laser remelting process parameters, the cooling rate gradient and atomic solubility gradient of the weld are collaboratively controlled; this method can simultaneously improve the strength, toughness and fatigue performance of the weld.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a method for improving the strength, toughness and fatigue resistance of aluminum alloy welds. Background Art

[0002] Aluminum alloys are widely used in the manufacture of key load-bearing components in the fields of ships, new energy vehicles, and high-speed trains due to their excellent strength, toughness, corrosion resistance, and weldability. With the rapid development of lightweight technology in related fields, key load-bearing components have put forward higher requirements on the strength and fatigue performance of aluminum alloy welded joints, which poses a severe challenge to existing aluminum alloy fusion welding technology. Although the weld porosity has been reduced to below 0.1% through process optimization, and the pore size is less than 1μm, the joint strength and fatigue performance still do not meet the requirements. The conventional solution is to suppress crack propagation through grain refinement, strengthening phase regulation, and nanoparticle doping, but the resulting near-homogeneous welds still have obvious limitations: once the crack initiates, it quickly penetrates along the homogeneous structure, making it difficult to break through the joint strength and fatigue performance.

[0003] Currently, research shows that metal materials designed with gradient configurations exhibit excellent mechanical properties. This gradient structural feature is manifested as significant differences in material properties or tissue morphology between different regions, and is typically characterized by a multi-scale (macro to micro) distribution of structural inhomogeneities. Structures designed with gradient configurations can significantly improve the strength, toughness, and fatigue resistance of materials. This innovative design concept stems from the imitation of natural biocomposites. Those biomineralized tissues that have undergone billions of years of evolution have achieved excellent environmental adaptability in harsh environments through their sophisticated hierarchical structures. The heterogeneous configurations exhibited by natural biomaterials often achieve synergistic optimization effects between performance parameters.

[0004] Based on this bionic principle, materials scientists regard gradient structure design as an innovative direction for regulating the comprehensive performance of alloys. By constructing controllable non-uniform features at different scales, researchers are committed to breaking through the inherent limitations of the performance parameters of traditional homogeneous materials. Patent CN116162872A uses a multi-stage hot processing process to prepare a multi-level heterogeneous structure, thereby improving the hardness and strength of the aluminum alloy. Patent CN116479281A prepares a mixed crystal heterogeneous structure by adding TiB2 and TiC ceramic particles, combined with extrusion and solution treatment processes, which synergistically improves the strength and toughness of the aluminum alloy. Patent CN117961292A prepares aluminum alloy welds with a combination of multi-level heterogeneous structures, solving the problem of mismatch between strength and plasticity of heat-treatable strengthened aluminum alloy fusion welds. However, the above method still finds it difficult to prepare welds with multi-level gradient heterogeneous structures, and cannot meet the welding manufacturing requirements of high strength, high toughness and high fatigue resistance of aluminum alloys. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a method for improving the strength, toughness and fatigue resistance of aluminum alloy welds. This method can simultaneously improve the strength, toughness and fatigue performance of welds to meet the welding manufacturing needs in fields such as ships, new energy vehicles and high-speed trains.

[0006] The object of the present invention is to provide a method for improving the strength, toughness and fatigue resistance of aluminum alloy welds, comprising the following steps:

[0007] S1. Use Al-Si-Cu-Mg series welding wire to fill and weld the aluminum alloy base material, inducing the precipitation of strengthening phase in the weld, and the grains in the weld are cellular grains;

[0008] S2. Laser remelting is performed on the weld surface of the filler weld to remelt and solidify the weld surface. On the one hand, the pores are effectively released to reduce the porosity and make the cellular grain size gradiently distributed along the depth direction of the weld. On the other hand, the solid solubility of Si, Cu, Mg and Zn atoms is gradiently distributed along the depth direction of the weld, thereby making the number and size of the strengthening phase gradiently distributed along the depth direction of the weld.

[0009] By adjusting the filling welding and laser remelting process parameters, the cooling rate gradient and atomic solubility gradient of the weld are controlled in a coordinated manner; by regulating the characteristics of the dual gradient structure of "surface submicron cellular grains / high-density strengthening phase → internal micron cellular grains / low-density strengthening phase", the strength and fatigue performance of the aluminum alloy weld are greatly improved.

[0010] In one embodiment of the present invention, in S1, the elemental composition and mass percentage of the Al-Si-Cu-Mg welding wire are: Si 0.9%-15.0%, Cu 0.4%-4.5%, Mg 0.6%-1.6%, Zn 0.1%-2.5%, Cr 0.1%-0.5%, Mn0.1%-1.0%, Fe 0-0.15%, the balance is Al and other unavoidable impurities, and the total impurities are 0-0.15%; the mass ratio of element Cu to element Mg is (1.5-7.5):1.

[0011] In one embodiment of the present invention, in S1, the aluminum alloy base material is selected from one or more of 2XXX series aluminum alloy, 4XXX series aluminum alloy, 5XXX series aluminum alloy, 6XXX series aluminum alloy, 7XXX series aluminum alloy and 8XXX series aluminum alloy.

[0012] In one embodiment of the present invention, in S1, the filling welding method is selected from one or more of laser welding, CMT welding, MIG welding and TIG welding.

[0013] In one embodiment of the present invention, the process parameters of the laser welding are: welding speed of 18mm / s-22mm / s, laser power of 2800W-3200W, oscillation frequency of 240Hz-260Hz, oscillation amplitude of 2.8mm-3.2mm, and defocus amount of 0.

[0014] In one embodiment of the present invention, in S1, the strengthening phase is one or more of β", θ', Q' and η' phases;

[0015] In one embodiment of the present invention, in S2, the weld surface is selected from the weld upper surface and / or the weld lower surface.

[0016] In one embodiment of the present invention, in S2, the laser remelting method is selected from remelting during welding and / or remelting after welding; the laser for the laser remelting is selected from one or more of infrared laser, semiconductor laser, blue laser and green laser.

[0017] In one embodiment of the present invention, in S2, the process parameters of the laser remelting are: laser power of 1800W-6000W, and scanning speed of 60mm / s-1000mm / s.

[0018] In one embodiment of the present invention, during the laser remelting process, the cooling rate gradient of the weld is 10 8 K / s-10 3 K / s.

[0019] In one embodiment of the present invention, during the laser remelting process, the atomic solid solubility gradient of the weld is: Si 1.85%-0.9%, Cu 4.5%-0.4%, Mg 1.6%-0.6%, Zn 2.5%-0.1%.

[0020] The technical solution of the present invention has the following advantages over the prior art:

[0021] (1) The laser remelting method of the present invention can effectively release the pores remaining on the surface of the weld, thereby effectively suppressing defects such as pores and greatly improving the welding quality.

[0022] (2) The method described in the present invention coordinates Al-Si-Cu-Mg series welding wire, filling welding and laser remelting technology: by filling welding with Al-Si-Cu-Mg series welding wire, cellular grains are generated in the weld and strengthening phases are rapidly precipitated; combined with laser remelting technology, rapid gradient cooling is generated, so that the micron cellular grains on the weld surface are transformed into submicron-sized ones, forming a gradient distribution of cellular grain size; at the same time, the solid solubility of Si, Cu, Mg and Zn atoms is gradient distributed along the depth direction of the weld, so that the number and size of strengthening phases are gradient distributed along the depth direction of the weld. Thus, a double gradient structure weld with gradient cellular grains + gradient strengthening phases is prepared, thereby overcoming the limitation of the near-homogeneous weld formed by traditional welding: once the crack initiates, it quickly penetrates along the homogeneous structure.

[0023] (3) The method described in the present invention controls the cooling rate gradient and atomic solubility gradient of the weld by regulating the process parameters such as the power and scanning speed of laser remelting, thereby regulating the cellular grain size gradient and the gradient characteristics of the strengthening phase distribution, thereby significantly improving the strength, toughness and high-cycle fatigue performance of the aluminum alloy weld, and solving the technical bottleneck that the high-cycle fatigue strength of the aluminum alloy weld is difficult to break through 130MPa.

[0024] (4) The laser remelting method used in the present invention can be carried out simultaneously with welding. At the same time, the laser scanning speed is fast and the heat input is low. Therefore, by combining filling welding and laser remelting, the heat affected zone of welding is not expanded, which greatly improves the welding quality and efficiency.

[0025] (5) The method described in the present invention is flexible and efficient, and can realize the simultaneous integration of welding and remelting of large structural parts, complex joints and micro-areas, and supports online monitoring of weld temperature during on-site welding, meeting the fatigue-resistant welding manufacturing requirements of high-end equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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:

[0027] Figure 1 The longitudinal cross-sectional cellular grain morphology of the welded joint in Test Example 1 of the present invention; wherein (a) is Comparative Example 2, and (b) is Example 2;

[0028] Figure 2 This is a diagram of the tensile mechanical properties of the welded joint in Test Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0030] Example 1

[0031] The method of improving the strength, toughness and fatigue resistance of aluminum alloy welds of the present invention specifically comprises the following steps:

[0032] S1. Oscillating laser welding was performed on an Al-Mg-Si-Cu aluminum alloy base material with a size of 3 mm × 50 mm × 50 mm using an Al-Si-Cu-Mg welding wire with a diameter of 1.2 mm. The welding speed was 20 mm / s, the laser power was 3000 W, the oscillation frequency was 250 Hz, the oscillation amplitude was 3.0 mm, and the defocus was 0. The precipitation of a strengthening phase was induced in the weld, and the grains in the weld were cellular grains. The elemental composition and mass percentage of the Al-Si-Cu-Mg welding wire were as follows: Si 9.0%, Cu 2%, Mg 0.8%, Zn 0.1%, Cr 0.1%, Mn 0.1%, Fe 0.1%, and the balance was Al and other unavoidable impurities, with a total impurity content of approximately 0.15%.

[0033] S2. Use infrared laser to remelt the upper surface of the weld after laser welding. The laser power is 3000W and the scanning speed is 200mm / s, so that the weld surface is quickly remelted and solidified. On the one hand, it can effectively release pores and reduce porosity (<1%), and make the cellular grain size gradient distributed along the depth direction of the weld. On the other hand, it can achieve the gradient distribution of Si, Cu, Mg, and Zn atomic solubility in the depth direction of the weld, so that the number and size of the strengthening phase are gradient distributed along the depth direction of the weld.

[0034] By adjusting the filling welding and laser remelting process parameters, the cooling rate gradient of the weld is controlled synergistically (10 4 K / s-10 3 The combined effects of a K / s ratio and an atomic solubility gradient (Si 1.85%-0.9%, Cu 1.23%-0.4%, Mg 0.82%-0.6%, Zn 0.1%) result in the formation of submicron cellular grains (~450nm) on the weld surface and micron cellular grains (~9.6μm) within the weld. Furthermore, high-density, fine strengthening phases such as θ', β", and Q' form in the weld's remelting zone, while low-density, larger strengthening phases such as β" form in the internal non-remelting zone, significantly improving the strength of the aluminum alloy weld.

[0035] Example 2

[0036] The method of improving the strength, toughness and fatigue resistance of aluminum alloy welds of the present invention specifically comprises the following steps:

[0037] S1. Oscillating laser welding was performed on an Al-Mg-Si-Cu aluminum alloy base material with a size of 3 mm × 50 mm × 50 mm using an Al-Si-Cu-Mg welding wire with a diameter of 1.2 mm. The welding speed was 20 mm / s, the laser power was 3000 W, the oscillation frequency was 250 Hz, the oscillation amplitude was 3.0 mm, and the defocus was 0. The precipitation of a strengthening phase was induced in the weld, and the grains in the weld were cellular grains. The elemental composition and mass percentage of the Al-Si-Cu-Mg welding wire were as follows: Si 9.0%, Cu 2%, Mg 0.8%, Zn 0.1%, Cr 0.1%, Mn 0.1%, Fe 0.1%, and the balance was Al and other unavoidable impurities, with a total impurity content of approximately 0.15%.

[0038] S2. Use a blue laser (wavelength ~450nm) to perform post-weld remelting on the upper and lower surfaces of the weld after laser welding. The laser power is 1800W and the scanning speed is 100mm / s, so that the weld surface is quickly remelted and solidified. On the one hand, it can effectively release pores and reduce porosity (<1%), and make the cellular grain size gradient distributed along the depth direction of the weld. On the other hand, it can achieve a gradient distribution of the solid solubility of Si, Cu, Mg, and Zn atoms along the depth direction of the weld, so that the number and size of the strengthening phase are gradient distributed along the depth direction of the weld.

[0039] By adjusting the filling welding and laser remelting process parameters, the cooling rate gradient of the weld is controlled synergistically (10 4 K / s-10 3 K / s) and an atomic solubility gradient (Si 1.85%-0.9%, Cu 1.23%-0.4%, Mg 0.82%-0.6%, Zn 0.1%), resulting in the formation of submicron cellular grains (~720nm) on the weld surface and micron cellular grains (~10.2μm) within the weld. Simultaneously, high-density, fine strengthening phases such as θ' and β" form in the weld's remelting zone, while low-density, larger strengthening phases such as β" form in the internal non-remelting zone, significantly improving the high-cycle fatigue strength of the aluminum alloy weld.

[0040] Comparative Example 1

[0041] The method is basically the same as Example 1, except that no remelting during welding is performed.

[0042] Comparative Example 2

[0043] The method is basically the same as Example 2, except that no post-weld remelting is performed.

[0044] Comparative Example 3

[0045] The method is basically the same as Example 1, except that the Al-Si-Cu-Mg welding wire is replaced with ER4047 welding wire purchased from Berkenhof (China), and its elemental composition and mass percentage are: Si 11.6%, Mg 0.01%, Mn 0.02%, Fe 0.20%, and the balance is Al and other inevitable impurities, and the total impurities are <0.15%.

[0046] Test Example 1

[0047] The weld microstructures of the welded joints of Example 2 and Comparative Example 2 were characterized, and the results were as follows: Figure 1 As shown. Figure 1 It can be seen that the weld of comparative example 2 is nearly homogeneous grains, and the cellular grain size is micron-level (9.0μm); the weld of embodiment 2 forms submicron cellular grains in the laser remelting zone, and micron cellular grains in the non-remelting zone, thereby forming a cellular grain size gradient. Al-Mg-Si-Cu aluminum alloy is oscillated laser welded using Al-9Si-0.8Mg-2Cu welding wire. The base material dilution rate is about 0.52, and the average composition of the weld is Al-4.8Si-0.83Mg-1.2Cu. Under the sub-rapid solidification conditions of this composition, the weld still undergoes eutectic reaction (L→α-Al+Si), producing cellular grains of α-Al embedded by eutectic Si. Under the laser remelting rapid gradient cooling rate (10 4 K / s-10 3 K / s), the cellular grains on the weld surface transform into submicron-sized grains (~720nm), and the internal non-remelting zone is micron-sized (~10.2μm).

[0048] Test Example 2

[0049] According to the standard of GB / T 2651-2023, the tensile mechanical properties of the welded joints of Example 1 and Comparative Examples 1 and 3 were tested. Figure 2 As shown. Figure 2 It can be seen that the tensile strength of the weld in Example 1 reached 335 MPa and the elongation was 4.8%, while the tensile strength of the weld in Comparative Example 1 was 310 MPa and the elongation was 4.5%, indicating that the tensile strength of the weld increased by 8.1% and the elongation increased by 6.7% after the laser remelting process. The tensile strength of the weld in Comparative Example 3 was 284 MPa and the elongation was 3.3%, indicating that the use of Al-Si-Cu-Mg welding wire in combination with the same laser remelting process increased the tensile strength of the weld by 18.0% and the elongation by 45.5%.

[0050] In addition, the tensile strength of the heat-affected zone of the weld joint in comparative example 1 reached 83% of the strength of the base material, while the tensile strength of the heat-affected zone of the joint in embodiment 1 still maintained more than 80% of the strength of the base material, indicating that the method of the embodiment not only significantly improved the strength of the weld, but also did not expand the weld heat-affected zone, thereby greatly improving the welding quality.

[0051] Test Example 3

[0052] Referring to the standard of GB / T 3075, the high cycle fatigue performance of the welded joints of Example 2 and Comparative Example 2 was tested, with a stress ratio R of 0.1 and a frequency f of 40 Hz. The results are shown in Table 1:

[0053] Table 1

[0054]

[0055] As can be seen from Table 1, the high-cycle fatigue of the welded joint of Example 2 reaches more than 140 MPa, and the high-cycle fatigue of the welded joint of Comparative Example 2 reaches 120 MPa, indicating that the method of the embodiment greatly improves the high-cycle fatigue performance of the aluminum alloy weld, and solves the technical bottleneck that the high-cycle fatigue strength of the 6XXX aluminum alloy fusion weld is difficult to break through 130 MPa.

[0056] In summary, the present invention coordinates Al-Si-Cu-Mg welding wire, filling welding and laser remelting technology to construct a dual-gradient structure weld with gradient cellular grains + gradient strengthening phase, which greatly improves the strength, toughness and high-cycle fatigue performance of the aluminum alloy weld.

[0057] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for improving the strength, toughness and fatigue resistance of aluminum alloy welds, characterized in that: The following steps are involved: S1. Use Al-Si-Cu-Mg series welding wire to fill and weld the aluminum alloy base material, inducing the precipitation of strengthening phase in the weld, and the grains in the weld are cellular grains; S2. Laser remelting is performed on the weld surface of the filler weld to remelt and solidify the weld surface; by adjusting the filler weld and laser remelting process parameters, the cooling rate gradient and atomic solid solubility gradient of the weld are controlled in a coordinated manner; the laser remelting process parameters are as follows: laser power of 1800W-6000W, scanning speed of 60mm / s-1000mm / s; during the laser remelting process, the cooling rate gradient of the weld is 10 8 K / s-10 3 K / s, and the atomic solid solubility gradient is Si 1.85%-0.9%, Cu 4.5%-0.4%, Mg1.6%-0.6%, and Zn 2.5%-0.1%.

2. The method for improving the strength, toughness and fatigue resistance of aluminum alloy welds according to claim 1, characterized in that: In S1, the elemental composition and mass percentage of the Al-Si-Cu-Mg welding wire are: Si 0.9%-15.0%, Cu 0.4%-4.5%, Mg 0.6%-1.6%, Zn 0.1%-2.5%, Cr 0.1%-0.5%, Mn 0.1%-1.0%, Fe 0-0.15%, the balance being Al and other unavoidable impurities, with a total impurity ratio of 0-0.15%; the mass ratio of element Cu to element Mg is (1.5-7.5):

1.

3. The method for improving the strength, toughness and fatigue resistance of aluminum alloy welds according to claim 1, characterized in that: In S1, the aluminum alloy base material is selected from one or more of 2XXX series aluminum alloy, 4XXX series aluminum alloy, 5XXX series aluminum alloy, 6XXX series aluminum alloy, 7XXX series aluminum alloy and 8XXX series aluminum alloy.

4. The method for improving the strength, toughness and fatigue resistance of aluminum alloy welds according to claim 1, characterized in that: In S1, the filling welding method is selected from one or more of laser welding, CMT welding, MIG welding and TIG welding.

5. The method for improving the strength, toughness and fatigue resistance of aluminum alloy welds according to claim 1, characterized in that: In S1, the strengthening phase is one or more of β", θ', Q' and η' phases.

6. The method for improving the strength, toughness and fatigue resistance of aluminum alloy welds according to claim 1, characterized in that: In S2, the weld surface is selected from the weld upper surface and / or the weld lower surface.

7. The method for improving the strength, toughness and fatigue resistance of aluminum alloy welds according to claim 1, characterized in that: In S2, the laser remelting method is selected from remelting during welding and / or remelting after welding; the laser for the laser remelting is selected from one or more of infrared laser, semiconductor laser, blue laser and green laser.

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