A method and device for collaboratively preparing weld multi-level heterogeneous structures using dual laser beams

Abstract

The invention discloses a method and device for collaboratively preparing a weld multi-level heterogeneous structure by using dual laser beams, and relates to the field of aluminum alloy material welding. The preparation device comprises an optical fiber laser with a galvanometer system, a short-wave laser, a dual-band composite swing welding head, an optical path system, a robot control system, a cooling system and a protection device. The preparation method comprises: using an optical fiber laser to perform swing filling welding, wherein the weld filling material is an Al-Si-Mg-Cu-Zn-Sn alloy, so as to obtain a weld with a heterogeneous grain structure; at the same time, using a short-wave laser to bake the weld online, so as to promote the composite precipitation of multiple nanophases and to distribute them in a gradient in the depth direction of the weld. By using the device and the method, an aluminum alloy weld with a multi-level heterogeneous structure combination can be prepared, and the comprehensive performance of the weld joint is collaboratively improved, thereby solving the problem of mismatch between the strength and plasticity of the heat-treatable and strengthened aluminum alloy fusion weld.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material welding, and in particular to a method and a device for collaboratively preparing a weld multi-level heterogeneous structure with dual laser beams. Background Art

[0002] With the development of the industrial age, cars are becoming more and more popular in our lives, but this also brings about high energy consumption and environmental pollution problems. Lightweighting of the car body is considered an effective strategy to reduce automobile energy consumption and pollution. Therefore, aluminum alloys with low density and high strength have been widely used. However, under the action of welding heat source, the softening problem of aluminum alloy welds seriously deteriorates the mechanical properties of welded joints. So far, people have used traditional methods such as grain boundary strengthening, precipitation phase strengthening, solid solution strengthening, and deformation strengthening to improve the mechanical properties of welded joints. Although these methods improve the strength and hardness of the weld, they sacrifice plasticity, resulting in the problem of inversion of weld strength and plasticity.

[0003] In recent years, it has been found that the mechanical properties of metal materials with gradient heterostructures exceed expectations, and the synergistic effect of inhomogeneous regions can simultaneously improve the strength and plasticity of welds. Heterostructures are characterized by significant material / structural differences between regions, usually in the form of macro / microstructural heterogeneity. The design of such heterostructures is inspired by heterostructured biomaterials found in nature, which have evolved through millions of years of natural selection to survive in harsh environments. Heterostructures endow biomaterials with unprecedented performance and functional synergies.

[0004] Inspired by nature, researchers use heterogeneous structures as a new strategy to customize the properties of aluminum alloys. Patent CN·116162872·A uses a solid solution-rapid heating large deformation-aging process to prepare a multi-level heterogeneous strengthening structure, which improves the mechanical properties of aluminum alloys such as hardness and strength. Patent CN·116479281·A adds TiB in the preparation of aluminum alloys. 2 After extrusion and solution heat treatment, an alloy with mixed crystal heterostructure characteristics is prepared, which simultaneously improves the strength and elongation of aluminum alloy profiles. However, the existing methods are not suitable for preparing the heterogeneous structure of welds and cannot meet the welding manufacturing needs of automobile bodies. Summary of the invention

[0005] The purpose of the present invention is to propose a method and device for preparing a weld multi-level heterogeneous structure by using dual laser beams, aiming to simultaneously improve the strength and plasticity of the weld to meet the welding manufacturing requirements of the automobile body. To achieve this purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing a weld multi-level heterogeneous structure by using dual laser beams in collaboration, comprising the following steps:

[0007] Step (1): Swinging laser filling welding: Swinging laser is used to fill the aluminum alloy plate with welding, and the reheating effect of the beam swing is used to continuously melt the solidified grains in the molten pool to form broken crystals, providing nucleation conditions for the formation of fine equiaxed crystal bands;

[0008] Step (2): laser online baking of the solid weld: the weld obtained by laser welding is repeatedly scanned by laser to achieve rapid short-term baking of the weld, so that the temperature field generated by the baking is distributed in a gradient in the depth direction of the weld;

[0009] Step (3): Adjust the laser welding-laser baking process parameters, coordinately regulate the molten pool solidification parameters and the weld temperature field, so as to promote the survival of broken dendrites, form fine equiaxed crystal bands at the bottom of the remelted molten pool, and meet the temperature conditions for the precipitation of nanophases, thereby promoting the precipitation of multiple nanophases, and distributing them in a gradient in the depth direction of the weld. Through the above steps, the aluminum alloy weld forms a heterogeneous grain structure with a mixture of fine equiaxed crystal bands and coarse grains and a gradient precipitation phase structure, thereby forming a multi-level heterogeneous structure.

[0010] Furthermore, the aluminum alloy described in step (1) is a heat-treatable aluminum alloy, including 2XXX series, 4XXX series, 5XXX series, 6XXX series, and 7XXX series aluminum alloys.

[0011] Furthermore, the reheating temperature brought about by the power, oscillation frequency and oscillation amplitude of the oscillating laser welding in step (1) must match the solidification range of the material.

[0012] Furthermore, the oscillating laser filling welding method in step (1) is one or more of oscillating laser wire filling welding, oscillating laser powder filling welding, oscillating laser sheet filling welding, oscillating laser-CMT composite, oscillating laser-MIG composite, and oscillating laser-TIG composite.

[0013] Furthermore, the filling material in step (1) is an Al-Si-Mg-Cu-Zn-Sn alloy or an Al-Mg-Si-Cu-Zn-Sn alloy.

[0014] Furthermore, the filling material in step (1) is in the form of one or more of 10-200um powder, 50-1000um flakes and 0.5-3.2mm diameter welding wire.

[0015] Furthermore, the type of baking laser used in step (2) is one or more of infrared laser, blue laser and green laser.

[0016] Furthermore, the parameters for regulating the molten pool solidification in step (3) include temperature gradient, solidification rate and cooling rate.

[0017] Furthermore, the temperature condition of the rapid short-time baking in step (2) is 100-350° C., and the baking time is 0-30 min.

[0018] A device for collaboratively preparing a weld multi-level heterogeneous structure using dual laser beams comprises a fiber laser with a galvanometer system, a short-wave laser, an optical path system, a dual-band composite oscillating welding head, a control system, a cooling system and a protective device. The fiber laser and the short-wave laser are installed side by side on the upper part of the optical path system, the dual-band composite oscillating welding head is installed on the lower part of the optical path system, the control system is communicatively connected with the optical path system, the cooling system is installed on the fiber laser and the short-wave laser, and the protective device is connected to the optical path system.

[0019] Furthermore, the cooling system is a cooling water pipe, and the protection device is an inert gas protection pipeline.

[0020] The beneficial effects of the invention are:

[0021] 1. By synergistically utilizing swing laser welding and laser online baking welds, a multi-level heterogeneous structure with heterogeneous grains + gradient precipitation phases is prepared, which significantly improves the strength and ductility of the welds and solves the problem of strength-plastic inversion of heat-treatable strengthened aluminum alloy fusion welds;

[0022] 2. The characteristics of heterogeneous structures are adjustable and the heat affected zone of welding is not enlarged;

[0023] 3. Swinging laser welding can effectively suppress defects such as pores, increase the supersaturation of the aluminum matrix, promote the rapid precipitation of multiple strengthening phases during laser baking, and greatly improve welding quality and efficiency;

[0024] 4. Flexible and efficient, it can realize the synchronous integration of welding and baking of large structural parts, complex joints and micro-areas, and support online monitoring of on-site welding process and baking temperature to meet the welding manufacturing needs of high-end equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention.

[0026] Figure 1 A flow chart of a method for preparing a weld multi-level heterogeneous structure with dual laser beams in cooperation with the present invention;

[0027] Figure 2A schematic diagram of the mechanism of a device for collaboratively preparing a weld multi-level heterogeneous structure with dual laser beams according to the present invention;

[0028] Figure 3 This is a longitudinal cross-sectional grain morphology diagram of Comparative Example 1 of the present invention;

[0029] Figure 4 This is a longitudinal cross-sectional grain morphology diagram of Example 1 of the present invention;

[0030] Figure 5 The cross-sectional microhardness diagrams of Example 1, Example 2 and Comparative Example 1 of the present invention;

[0031] Figure 6 This is a diagram of the tensile mechanical properties of Example 1, Example 2 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0032] In order to make the technical problems solved by the present invention, the technical solutions adopted and the technical effects achieved clearer, the technical solutions of the embodiments of the present invention are further described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0033] A device for collaboratively preparing a weld multi-level heterogeneous structure using dual laser beams comprises a fiber laser 1 with a galvanometer system, a short-wave laser 2, an optical path system 3, a dual-band composite oscillating welding head 4, a control system 5, a cooling system 6 and a protective device 7. The fiber laser and the short-wave laser are installed side by side on the upper part of the optical path system, the dual-band composite oscillating welding head is installed on the lower part of the optical path system, the control system is communicatively connected with the optical path system, the cooling system is installed on the fiber laser and the short-wave laser, and the protective device is connected to the optical path system.

[0034] The cooling system is a cooling water pipe, the protection device is an inert gas protection pipeline, and the control system is a computer.

[0035] Example 1: This example is a method for obtaining a multi-level heterogeneous structure strengthening organization. The welding base material used is a 3mm thick Al-Mg-Si-Cu alloy plate with a size of 50mm×50mm. The filling material is an Al-Si-Mg-Cu-Zn aluminum alloy welding wire with a diameter of 1.2mm.

[0036] The specific implementation steps of this embodiment are:

[0037] (1) The oscillating laser wire filling welding was performed using the following process parameters: laser power of 2800 W, welding speed of 50 mm / s, defocus of 0 mm, oscillation frequency of 100 Hz, and oscillation amplitude of 1.2 mm.

[0038] (2) Using blue laser (wavelength ~450nm) to bake the solid weld online. The weld was baked online using the process parameters of 500W blue laser power and 60mm / s scanning speed.

[0039] (3) The spacing between the oscillating laser and blue laser beams was adjusted to control the solidification conditions of the molten pool, and a heterogeneous grain structure weld with a mixture of fine equiaxed crystal bands and coarse grain areas was obtained. At the same time, the defocus of the blue laser was adjusted, and the weld was baked online for 1 min to promote the composite precipitation of multiple strengthening phases and their gradient distribution along the depth direction of the weld, so that the microhardness also showed a gradient distribution along the depth direction of the weld.

[0040] Example 2: This example is a method for obtaining a multi-level heterogeneous structure strengthening organization. The welding base material used is a 3mm thick Al-Mg-Si-Cu alloy plate with a size of 50mm×50mm. The filling material is an Al-Si-Mg-Cu-Zn aluminum alloy welding wire with a diameter of 1.2mm.

[0041] The specific implementation steps of this embodiment are:

[0042] (1) The process parameters of oscillating laser wire filling welding are as follows: laser power of 2800 W, welding speed of 50 mm / s, defocus of 0 mm, oscillation frequency of 100 Hz, and oscillation amplitude of 1.2 mm.

[0043] (2) Using blue laser (wavelength ~450nm) to bake the solid weld online. The weld was baked online using the process parameters of 500W blue laser power and 60mm / s scanning speed.

[0044] (3) The spacing between the oscillating laser and blue laser beams was adjusted to control the solidification conditions of the molten pool, and a heterogeneous grain structure weld with a mixture of fine equiaxed crystal bands and coarse grain areas was obtained. At the same time, the defocus of the blue laser was adjusted, and the weld was baked online for 5 minutes to promote the composite precipitation of multiple strengthening phases and their gradient distribution along the depth direction of the weld, so that the microhardness also showed a gradient distribution along the depth direction of the weld.

[0045] Comparative Example 1: For comparison with Example 1, the material used is a 3 mm thick Al-Mg-Si-Cu alloy plate with a size of 50 mm×50 mm. The filling material is an Al-Si-Mg-Cu-Zn aluminum alloy welding wire with a diameter of 1.2 mm.

[0046] This comparative example uses laser direct welding:

[0047] The welding was performed with a laser power of 2800 W, a welding speed of 50 mm / s and a defocus of 0 mm to directly obtain the welded joint.

[0048] By comparison, it can be found that the swing laser welding and laser online baking weld of the present invention prepare a structure with a multi-level heterogeneous structure, which synergistically improves the strengthening and plasticity of the heat-treatable strengthened aluminum alloy weld.

[0049] The technical principle of the present invention is described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the scope of protection of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without paying creative labor, and these methods will fall within the scope of protection of the present invention.

Claims

1. A method for preparing a weld multi-level heterogeneous structure by using dual laser beams, characterized in that: The following steps are involved: Step (1): Swinging laser filling welding: Swinging laser is used to fill the aluminum alloy plate with welding, and the reheating effect of the beam swing is used to continuously melt the solidified grains in the molten pool to form broken crystals, providing nucleation conditions for the formation of fine equiaxed crystal bands; The filling material in step (1) is an Al-Si-Mg-Cu-Zn-Sn alloy or an Al-Mg-Si-Cu-Zn-Sn alloy, and the filling material is in the form of one or more of 10-200um powder, 50-1000um flakes, and 0.5-3.2mm diameter welding wire; Step (2): laser online baking of the solid weld: the weld obtained by laser welding is repeatedly scanned by laser to achieve rapid short-term baking of the weld, so that the temperature field generated by the baking is distributed in a gradient in the depth direction of the weld; The temperature condition of the rapid short-time baking in step (2) is 100-350° C., and the baking time is 0-30 min; Step (3): Adjust the laser welding and laser baking process parameters, coordinately regulate the molten pool solidification parameters and the weld temperature field, so as to promote the survival of broken dendrites, form fine equiaxed crystal bands at the bottom of the remelted molten pool, and meet the temperature conditions for the precipitation of nanophases, thereby promoting the precipitation of multiple nanophases, and distributing them in a gradient in the depth direction of the weld, so that the aluminum alloy weld forms a mixed heterogeneous grain and gradient precipitation phase structure of fine equiaxed crystal bands and coarse grain areas, thereby forming a multi-level heterogeneous structure.

2. The method for preparing a weld multi-level heterogeneous structure by using dual laser beams in collaboration according to claim 1, characterized in that: The aluminum alloy described in step (1) is a heat-treatable aluminum alloy, which is one or more of 2XXX series, 4XXX series, 5XXX series, 6XXX series and 7XXX series aluminum alloys.

3. The method for preparing a weld multi-level heterogeneous structure by using dual laser beams in collaboration according to claim 1, characterized in that: The reheating temperature brought about by the power, oscillation frequency and oscillation amplitude of the oscillating laser welding in step (1) matches the solidification range of the material.

4. The method for preparing a weld multi-level heterogeneous structure by using dual laser beams in collaboration according to claim 1, characterized in that: The oscillating laser filling welding method in step (1) is one or more of oscillating laser wire filling welding, oscillating laser powder filling welding, oscillating laser sheet filling welding, oscillating laser-CMT composite, oscillating laser-MIG composite, and oscillating laser-TIG composite.

5. The method for preparing a weld multi-level heterogeneous structure by using dual laser beams in collaboration according to claim 1, characterized in that: The baking laser used in step (2) is one or more of infrared laser, blue laser and green laser.

6. The method for preparing a weld multi-level heterogeneous structure by using dual laser beams in collaboration according to claim 1, characterized in that: The parameters for regulating the molten pool solidification in step (3) include temperature gradient, solidification rate and cooling rate.

7. A device for preparing a weld multi-level heterogeneous structure by synergistic use of dual laser beams, characterized in that: The invention comprises a fiber laser with a galvanometer system, a short-wave laser, an optical path system, a dual-band composite oscillating welding head, a control system, a cooling system and a protective device. The fiber laser and the short-wave laser are installed side by side on the upper part of the optical path system, the dual-band composite oscillating welding head is installed on the lower part of the optical path system, the control system is communicatively connected with the optical path system, the cooling system is installed on the fiber laser and the short-wave laser, and the protective device is connected to the optical path system.

8. The device for preparing a weld multi-level heterogeneous structure by synergistically using dual laser beams according to claim 7, characterized in that: The cooling system is a cooling water pipe, and the protection device is an inert gas protection pipeline.

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