A method for improving the strength and corrosion resistance of 6XXX series aluminum alloy welds

Abstract

The present invention relates to a method for improving the strength and corrosion resistance of 6XXX series aluminum alloy welds, and belongs to the field of welding technology. The method of the present invention comprises the following steps: S1, measuring the composition of the 6XXX series aluminum alloy base material, and determining the composition range of the filler material according to the composition of the base material and the composition of the ideal weld; the Ti content in the ideal weld is 0.3wt%-0.6wt%, the Mg content is 1.75wt%-3.05wt%, and the mass ratio of Mg to Si is (1.8-3.2):1; S2, determining the shape of the filler material according to the welding form, and preparing the filler material; S3, welding the 6XXX series aluminum alloy base material with the filler material. By regulating the content of elements such as Ti and Mg in the weld and optimizing the welding process, the weld can achieve a synergistic improvement in strength and corrosion resistance under multiple strengthening systems, so as to meet the lightweight structure welding manufacturing needs in the fields of automobiles, ships, and high-speed trains.

Description

Technical Field

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

[0002] Lightweighting is an important means of achieving energy conservation and emission reduction in the transportation industry, and the use of lightweight materials is a crucial component of this approach. 6XXX series aluminum alloys (such as 6061, 6082, and 6D10) have become important lightweight materials due to their light weight, high specific strength, and ease of processing. They are widely used in automobiles, ships, high-speed trains, and other fields. Welding technology is an important method for joining aluminum alloy structural parts. However, aluminum alloys also have the characteristics of high thermal conductivity, rapid solidification rate, high laser reflectivity, and a large difference in hydrogen solubility between solid and liquid phases. During the welding process, weld grain coarsening and dissolution of nanoscale strengthening phases occur, leading to weld softening and porosity defects, seriously compromising the quality of the welded joint. Furthermore, the heterogeneous microstructure and composition introduced during welding alter the corrosion resistance of the alloy. The weld is often more susceptible to corrosion cracking than the substrate, reducing the service life of the joint.

[0003] In existing technologies, weld strength is primarily improved through optimization of welding processes, weld microalloying, and heat treatment. Patent CN117620517A refines weld grain size and Fe-rich phases using the rare earth element Y, improving weld mechanical properties. Patent CN104827200A increases weld tensile strength by 50 MPa by adding Sc to conventional 4047 welding wire. Patent CN119020644A achieves a weld coefficient exceeding 0.8 through post-weld heat treatment and Er element modification. Patent CN117512481A improves weld tensile strength and reduces weld exfoliation corrosion through post-weld heat treatment.

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

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

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

[0007] The object of the present invention is to provide a method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloys, comprising the following steps:

[0008] S1. Determine the composition of a 6XXX series aluminum alloy base material, and determine the composition range of the filler material based on the base material composition and the composition of the ideal weld; the Ti content in the ideal weld is 0.3wt%-0.6wt%, the Mg content is 1.75wt%-3.05wt%, and the mass ratio of Mg to Si is (1.8-3.2):1;

[0009] S2. Determine the shape of the filling material according to the welding form and prepare the filling material;

[0010] S3. Use filler material to weld 6XXX series aluminum alloy base material.

[0011] In one embodiment of the present invention, in S1, the ideal weld is achieved by controlling the Ti content to refine the grain size; controlling the Mg content to reduce the formation of harmful phases, stabilize the formation of beneficial phases, reduce electrochemical corrosion, and improve the strength and toughness of the weld. When the Mg content is low, free eutectic Si exists in the weld, and the non-precipitated zone near it undergoes anodic dissolution. At the same time, the presence of Si accelerates the polarity conversion between the Mg2Si phase and the matrix. When the Mg content is high, Al3Mg2 phase and S phase are generated at the grain boundaries. The electrode potential of these phases is much lower than that of the Al matrix, making them very susceptible to anodic dissolution. By controlling the Mg / Si ratio, the content and morphology of eutectic Si, Mg2Si, AlSiCuMg, AlCuMg, and Al3Mg2 phases in the weld are changed, suppressing electrochemical corrosion between them and the matrix. Only under these conditions can the S phase, Al3Mg2 phase, and eutectic Si in the weld be relatively small, thereby achieving improved corrosion resistance.

[0012] In one embodiment of the present invention, in S1, the composition of the filling material is calculated according to the following formula:

[0013] Filler material composition = (ideal weld composition - 6XXX series aluminum alloy base material composition × fusion ratio) / (1 - fusion ratio);

[0014] When the filler material is in the form of foil or sheet, fusion ratio = (weld area - filler material cross-sectional area) / weld area;

[0015] When the filler material is in the form of welding wire, the fusion ratio = (weld area - upper and lower height areas) / weld area.

[0016] The weld area is the weld area obtained after welding without adding filler material;

[0017] When the filler material is in the form of foil or sheet, the length is equal to the weld length, the width is less than 200μm, and the height is less than the thickness of the 6XXX series aluminum alloy base material. The cross-sectional area = width × height.

[0018] In one embodiment of the present invention, in S2, the welding form is selected from arc welding and / or laser welding.

[0019] In one embodiment of the present invention, in S2, the form of the filler material is selected from Al-Ti-Mg flakes and / or Al-Mg-Si-Cu-Ti welding wires.

[0020] In one embodiment of the present invention, the elemental composition and mass percentage of the Al-Mg-Si-Cu-Ti welding wire are: Mg 4.6wt%-6.1wt%, Si 0.7wt%-1.0wt%, Cu 0.4wt%-0.5wt%, Ti 0.6wt%-1.6wt%, Mn0.5wt%-0.6wt%, Cr 0.2wt%-0.3wt%, Fe 0-0.15wt%, Zn 0-0.1wt%, and the balance is Al and other inevitable impurities.

[0021] In one embodiment of the present invention, in S3, the welding heat input should be reduced within the range of weld penetration during welding. When arc welding is selected, a large welding current and a fast welding speed should be selected; when laser welding is selected, a high laser power and a fast welding speed should be selected. When the welding form is laser welding, the process parameters of the laser welding are: welding power of 2100W-2700W, welding speed of 33mm / s-50mm / s, shielding gas of argon, gas flow of 10L / min-25L / min, air gun angle of 20°, swing trajectory of circle, swing frequency of 100Hz-150Hz, swing amplitude of 1.0mm-1.6mm; under these conditions, the welding heat input can be controlled to ensure that the filler material and the 6XXX series aluminum alloy base material are fully mixed to reduce the softening degree of the heat-affected zone and reduce the porosity.

[0022] In one embodiment of the present invention, the 6XXX series aluminum alloy weld has a tensile strength of 280MPa-350MPa, a yield strength of 203MPa-237MPa, a microhardness of 84HV-109HV, and a corrosion current density of 0.55μA / cm 2 -1.85μA / cm2 , the welding coefficient is 68.0%-85.0%.

[0023] In one embodiment of the present invention, the porosity of the 6XXX series aluminum alloy weld is less than 1%.

[0024] In one embodiment of the present invention, the metallographic structure of the 6XXX series aluminum alloy weld is fully equiaxed crystals with a grain size of 10 μm-30 μm.

[0025] In one embodiment of the present invention, the precipitated phase of the 6XXX series aluminum alloy weld is selected from one or more of eutectic Si phase, Al3Ti phase, Mg2Si phase, Q phase (AlSiCuMg) and S phase (AlCuMg).

[0026] The technical solution of the present invention has the following advantages over the prior art:

[0027] (1) The method described in the present invention designs the content of Ti and Mg elements in the filler material so that the content of Ti and Mg elements in the 6XXX series aluminum alloy weld meets certain conditions, thereby achieving a synergistic improvement in the strength and corrosion resistance of the weld, especially exceeding 300 MPa in tensile strength.

[0028] (2) The method disclosed herein optimizes the welding process, allowing the Ti and Mg elements in the filler material to react with the 6XXX series aluminum alloy base material to form precipitated phases such as Al3Ti, Mg2Si, Q, and S phases. Ti promotes weld grain refinement through heterogeneous nucleation, while Mg dissolves into the matrix during rapid cooling after welding. The coupled effects of grain refinement and solid solution strengthening improve the mechanical properties of the weld.

[0029] (3) The method described in the present invention achieves a synergistic improvement in weld strength and corrosion resistance, eliminating the need for subsequent heat treatment operations, shortening the process flow and improving production efficiency. Furthermore, the materials used in the present invention are relatively inexpensive, reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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:

[0031] Figure 1 This is a grain size diagram of the weld in Test Example 1 of the present invention;

[0032] Figure 2 This is a SEM image of the weld in Test Example 2 of the present invention;

[0033] Figure 3 This is the XRD pattern of the weld in Test Example 2 of the present invention;

[0034] Figure 4 Graph showing the mechanical properties of the weld in Test Example 3 of the present invention;

[0035] Figure 5 This is a graph showing the corrosion resistance of the weld in Test Example 3 of the present invention. DETAILED DESCRIPTION

[0036] 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.

[0037] In the present invention, unless otherwise specified, the reference standard for welding used in the embodiments of the present invention is HG / T20222-2017.

[0038] In the present invention, unless otherwise specified, the 6XXX series aluminum alloy base material used in the embodiments of the present invention is a T6 state Al-Mg-Si-Cu alloy with a size of 100 mm × 60 mm × 2.5 mm; the element composition and its mass percentage are: Mg 0.81%, Si 0.97%, Cu 0.43%, Mn 0.50%, Cr 0.23%, Ti 0.03%, and the balance is Al and other inevitable impurities; the heat treatment process is: solution treatment at 560°C for 1 hour, followed by aging at 180°C for 6 hours; the relevant properties are: tensile strength of 408 MPa, yield strength of 385 MPa, and microhardness of 130 HV.

[0039] In the present invention, unless otherwise specified, the determination of the weld area involved in the embodiments of the present invention includes the following steps: mechanically grinding the surface of the 6XXX series aluminum alloy base material to remove the surface oxide layer, cleaning with alcohol and then drying; welding the 6XXX series aluminum alloy base material with an oscillating laser as a heat source, the welding form is butt welding, the welding power is 2700W, the welding speed is 50mm / s, the shielding gas is pure argon, the shielding gas flow rate is 20L / min, the air gun angle is 20°, the oscillation trajectory is circular, the oscillation frequency is 150Hz, and the oscillation amplitude is 1.6mm; using wire cutting to cut a 5mm×30mm×2.5mm sample perpendicular to the weld, and polishing the weld joint with 180#, 600#, 1000#, 2000#, 3000# and 5000# water abrasive paper in turn, and photographing the macroscopic morphology of the weld joint with a stereo microscope, and measuring the weld area to be 6.58mm 2 .

[0040] Example 1

[0041] The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloys in this embodiment specifically comprises the following steps:

[0042] S1. Determine the composition of the filler material based on the composition of the base material and the composition of the ideal weld. The Ti content in the ideal weld is 0.3wt%, the Mg content is 1.75wt%, and the mass ratio of Mg to Si is 1.8:1.

[0043] The composition of the filling material is calculated according to the following formula:

[0044] The length of the filler material is the same as the weld length, which is 100mm; the width is 0.1mm; the height is the thickness of the 6XXX series aluminum alloy base material, which is 2.5mm; its cross-sectional area = width × height = 0.1mm × 2.5mm = 0.25mm 2 ;

[0045] Fusion ratio = (weld area - filler material cross-sectional area) / weld area = (6.58mm 2 -0.25mm 2 ) / 6.58mm 2 =0.96;

[0046] The composition of the filler material = (composition of the ideal weld - composition of the 6XXX series aluminum alloy base material × fusion ratio) / (1 - fusion ratio); the results show that the Ti content in the filler material is 6.78wt%, the Mg content is 24.31wt%, and the balance is Al and other unavoidable impurities.

[0047] S2. The filler material is in the form of a thin sheet according to the welding form of laser welding, and the ingredients are prepared according to the composition of the filler material. The raw materials are 99.99% pure Al, Al-10Ti and 99.9% pure Mg; then, an Al-Ti-Mg alloy is obtained by gravity casting; then, a 100 mm × 2.5 mm × 0.2 mm Al-Ti-Mg sheet is taken from the middle of the Al-Ti-Mg alloy by wire cutting, and polished with 180# sandpaper to remove wire cutting marks. After polishing to 0.1 mm, it is cleaned with alcohol and blown dry;

[0048] S3. Filler material was used to weld 6XXX series aluminum alloy base material, with an oscillating laser as the heat source, a welding power of 2700 W, a welding speed of 50 mm / s, pure argon as the shielding gas, a shielding gas flow of 20 L / min, an air gun angle of 20°, a circular oscillation trajectory, an oscillation frequency of 150 Hz, and an oscillation amplitude of 1.6 mm.

[0049] Example 2

[0050] The same as Example 1, except for the following points:

[0051] In S1, the Ti content in the ideal weld is 0.6wt%, the Mg content is 3.05wt%, and the mass ratio of Mg to Si is 3.2:1;

[0052] The composition of the filling material is calculated according to the following formula:

[0053] The filling material has a width of 0.2 mm, a height of 2.5 mm, a length of 100 mm, and a cross-sectional area of 0.5 mm 2 The calculated fusion ratio is 0.92, the Ti content in the filler material is 7.16wt%, the Mg content is 28.81wt%, and the balance is Al and other unavoidable impurities;

[0054] In S2, a 100 mm × 2.5 mm × 0.3 mm Al-Ti-Mg slice was taken from the middle of the Al-Ti-Mg alloy by wire cutting, and polished with 180# sandpaper to remove the wire cutting marks. After polishing to 0.2 mm, it was cleaned with alcohol and blown dry.

[0055] Comparative Example 1

[0056] Basically the same as Example 2, except that no filling material is used.

[0057] Comparative Example 2

[0058] The same as Example 2, except for the following points:

[0059] The Ti content in the ideal weld is 0.6wt% and the Mg content is 0.81wt% (i.e. no additional Mg is added);

[0060] The composition of the filling material is calculated according to the following formula:

[0061] The filling material has a width of 0.2 mm, a height of 2.5 mm, a length of 100 mm, and a cross-sectional area of 0.5 mm 2 The calculated fusion ratio is 0.92, the Ti content in the filler material is 7.16wt%, and the balance is Al and other inevitable impurities.

[0062] Comparative Example 3

[0063] The same as Example 2, except for the following points:

[0064] The ideal weld contains 0.6wt% Ti and 3.5wt% Mg (i.e., excessive Mg is added);

[0065] The composition of the filling material is calculated according to the following formula:

[0066] The filling material has a width of 0.2 mm, a height of 2.5 mm, a length of 100 mm, and a cross-sectional area of 0.5 mm 2The calculated fusion ratio is 0.92, the Ti content in the filler material is 7.16wt%, the Mg content is 34.44wt%, and the balance is Al and other inevitable impurities.

[0067] Test Example 1

[0068] First, the welds prepared in Example 1 and Comparative Example 1 were electropolished using a 10 vol.% perchloric acid ethanol solution at a voltage of 20 V for 30 s. The crystal structure of the welds was then analyzed using electron backscatter diffraction (EBSD). The results are shown in Figure 2. Figure 1 As shown. Figure 1 It can be seen that the grain size of the weld prepared in Example 1 is about 28.2 μm, and the grain size of the weld prepared in Comparative Example 1 is about 68.7 μm. This is because the white Al3Ti phase precipitates in the weld after Ti modification in Example 1, which acts as a heterogeneous nucleation point for α-Al and significantly refines the weld grains.

[0069] Test Example 2

[0070] First, the microstructure of the weld prepared in Example 1 and Comparative Example 1 was observed by SEM, and then the precipitated phase of the weld prepared in Example 1-2 and Comparative Example 1-3 was qualitatively analyzed by XRD. Finally, the non-equilibrium solidification process of the weld was calculated by Thermo-Calc. The results are as follows: Figure 2-Figure 3 As shown. Figure 2-Figure 3 It can be seen that the precipitated phases in the weld prepared in Example 1 are primarily eutectic Si, Al3Ti, Mg2Si, and Q phase (AlSiCuMg); the precipitated phases in the weld prepared in Example 2 are primarily eutectic Si, Al3Ti, Mg2Si, and S phase (AlCuMg); the precipitated phases in the weld prepared in Comparative Example 1 are primarily eutectic Si, Mg2Si, and Q phase (AlSiCuMg); the precipitated phases in the weld prepared in Comparative Example 2 are primarily eutectic Si, Al3Ti, Mg2Si, and Q phase (AlSiCuMg); and the precipitated phases in the weld prepared in Comparative Example 3 are primarily Al3Ti, Mg2Si, S phase (AlCuMg), and Al3Mg2 phase. As the Mg content in the weld increases, the eutectic Si phase decreases, and the Q phase gradually transforms into the S phase. When the Mg content increases further, as in Comparative Example 3, the Al3Mg2 phase forms in the weld. This anodic phase significantly impairs the corrosion resistance of the weld.

[0071] Test Example 3

[0072] The porosity, strength, etc. of the welds prepared in Examples 1-2 and Comparative Examples 1-3 were tested:

[0073] (1) Porosity: A 5 mm × 100 mm × 2.5 mm sample was cut from the center of the weld using wire cutting, and polished according to the above method. The morphology was photographed using a stereo microscope, and the porosity was calculated based on the area ratio.

[0074] (2) Tensile strength and yield strength: The tensile strength and yield strength of the weld shall be tested in accordance with GB / 228.1-2021 "Tensile tests on metallic materials - Part 1: Test methods at room temperature";

[0075] (3) Microhardness: Test the microhardness of the weld according to GB / T4340.1-2009;

[0076] (4) Welding coefficient: the ratio of the tensile strength of the weld to the tensile strength of the base material;

[0077] (5) Corrosion current density: The electrochemical corrosion performance of the welded joint was tested using a Princeton versa STAT3 electrochemical workstation. The weld was cut separately along the welding direction using wire cutting, and its back was glued with conductive glue and wire, and it was inlaid with inlay material and then polished with sandpaper. The sample was immersed in 3.5% NaCl solution for 24 hours and then electrochemically tested. The test was carried out in the order of open circuit potential, EIS and Tafel.

[0078] Figure 4-Figure 5 Table 1 shows the relevant properties of the weld finally measured:

[0079] Table 1

[0080]

[0081] From Table 1 and Figure 4-Figure 5 It can be seen that the method of the embodiment can synergistically improve the mechanical properties and corrosion resistance of the weld.

[0082] By comparing Example 2 and Comparative Examples 1-2, it can be seen that when only the Ti element in the weld is controlled, the mechanical properties and corrosion resistance of the weld can also be synergistically improved, but at this time the welding coefficient is only 66.5%, and there is still a lot of room for improvement in mechanical properties.

[0083] Comparison of Example 2 and Comparative Example 3 shows that when the Ti content is within the theoretical range and the Mg element is excessive, the corrosion current density is 3.429 μA / cm 2 , but the corrosion resistance of the weld is greatly reduced.

[0084] 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 weld strength and corrosion resistance of 6XXX series aluminum alloys, characterized in that: The following steps are involved: S1. Determine the composition of a 6XXX series aluminum alloy base material, and determine the composition range of the filler material based on the base material composition and the composition of the ideal weld; the Ti content in the ideal weld is 0.3wt%-0.6wt%, the Mg content is 1.75wt%-3.05wt%, and the mass ratio of Mg to Si is (1.8-3.2):1; S2. Determine the shape of the filling material according to the welding form and prepare the filling material; S3. Welding 6XXX series aluminum alloy base metal with filler material; The composition of the filling material is calculated according to the following formula: Filler material composition = (ideal weld composition - 6XXX series aluminum alloy base material composition × fusion ratio) / (1 - fusion ratio); When the filler material is in the form of foil or sheet, fusion ratio = (weld area - filler material cross-sectional area) / weld area; When the filler material is in the form of welding wire, the fusion ratio = (weld area - upper and lower excess height areas) / weld area; the weld area is the weld area obtained after welding without adding filler material.

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

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

4. The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloy according to claim 3, characterized in that: The elemental composition and mass percentage of the Al-Mg-Si-Cu-Ti welding wire are: Mg 4.6wt%-6.1wt%, Si 0.7wt%-1.0wt%, Cu 0.4wt%-0.5wt%, Ti 0.6wt%-1.6wt%, Mn 0.5wt%-0.6wt%, Cr 0.2wt%-0.3wt%, Fe0-0.15wt%, Zn 0-0.1wt%, and the balance is Al and other inevitable impurities.

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

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

7. The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloys according to claim 1, wherein: The porosity of the 6XXX series aluminum alloy weld is less than 1%.

8. The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloys according to claim 1, wherein: The metallographic structure of the 6XXX series aluminum alloy weld is fully equiaxed crystals with a grain size of 10 μm-30 μm.

9. The method for improving the weld strength and corrosion resistance of 6XXX series aluminum alloys according to claim 1, wherein: The precipitated phase of the 6XXX series aluminum alloy weld is selected from one or more of eutectic Si phase, Al3Ti phase, Mg2Si phase, Q phase and S phase.

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