Novel low-density high-strength aluminum alloy composite welding method based on swing laser-CMT

Abstract

The invention discloses a novel low-density and high-strength aluminum alloy composite welding method based on swing laser-CMT, and aims to solve the welding problem of high-strength and low-density aluminum alloy in the field of rail transit. Through the coupling effect of laser high-energy density and CMT low-heat input, accurate control over welding heat input is achieved, and the specific method comprises the steps that the swing frequency, amplitude and path of a laser head are preset to control periodic swing of a laser beam, the welding current and the wire feeding speed of a CMT welding machine are set, the optimized laser power and the optimized welding speed are combined, and the CMT welding efficiency is improved. And the temperature gradient and the thermal stress in the welding process are reduced. The strength of the welded low-density aluminum alloy joint reaches 340.12 MPa, the joint coefficient reaches 0.8, and technical support is provided for light weight and high performance of rail transit.

Description

Technical Field

[0001] The invention relates to a low-density and high-strength aluminum alloy composite welding method, belonging to the technical field of laser welding. Background Art

[0002] Driven by the demand for lightweight high-speed trains, low-density and high-strength aluminum alloys have become a key basic material to support the development of strategic emerging industries such as the transportation sector, high-end equipment manufacturing and new materials. However, with the breakthrough improvement in the strength level of the material, its welding thermodynamic properties and solidification behavior have changed significantly, resulting in interface mismatch phenomena such as joint softening and intergranular segregation under conventional welding processes, which seriously restricts the engineering conversion efficiency of material performance.

[0003] With the rapid development of industrial manufacturing, aluminum alloy welding technology can be divided into: metal inert gas shielded welding (MIG), non-metal inert gas shielded welding (TIG), friction stir welding (FSW), laser beam welding, etc. according to the type of heat source. Since the MIG arc energy density is low and not concentrated, a large heat input is required during welding, which is prone to large welding deformation, severe joint softening and more thermal cracks; the arc is stable during TIG welding, the weld is beautiful and not easy to produce spatter, but the welding speed is slow and the welding efficiency is low due to the shallow melting depth, which makes it difficult to weld thick plates; the parent material will not melt during stir friction welding, so no shielding gas is required, which can reduce the appearance of pores and cracks to a certain extent. However, the welding speed is limited during welding, a key hole that is difficult to repair will be formed at the end of the weld due to the stirring probe, and a large upsetting force is required, which is not suitable for welding complex structures. When aluminum alloys are welded with laser beams, the high power density of the laser can be used for welding in a short time, which improves the welding efficiency and obtains a more beautiful weld. However, there will be the following defects in the welding process: hydrogen is precipitated in the molten pool to produce hydrogen pores and process pores; when the aluminum alloy solidifies, the large shrinkage rate will cause thermal cracks with large welding stress and welding deformation; the high reflectivity of aluminum alloy to laser photons leads to insufficient absorption of laser.

[0004] Therefore, it is urgent to propose a new low-density and high-strength aluminum alloy composite welding method to solve the above technical problems. Summary of the invention

[0005] The technical problem to be solved by the present invention is:

[0006] Aiming at the joint softening, pores and thermal crack defects caused by excessive heat input in high-strength aluminum alloy welding, a new low-density high-strength aluminum alloy composite welding method based on swing laser-CMT (cold metal transfer welding) is provided.

[0007] The technical solution of the present invention:

[0008] Step 1: Turn on the power switch, and then turn on the water cooler, laser, galvanometer controller, welder, and KUKA robot. Install the welding wire to the welder, then install the laser head and CMT welding gun and fix them rigidly with the fixture, and check the laser protection lens. Then fix the workpiece to the welding fixture.

[0009] Step 2: Preset basic parameters, including laser power, laser oscillation amplitude, laser oscillation frequency, defocusing amount, CMT arc current, wire feeding speed, and set welding speed and shielding gas flow rate; select welding program, set welding start and end points, and then reset the program; turn on the air compressor and shielding gas cylinder, and then turn on the laser galvanometer. During welding, the laser adopts arc oscillation mode, and finally set the automatic welding mode on the operating handle; when welding starts, trigger the laser first to focus the laser beam on the area to be welded, start the CMT welder synchronously, and coordinate the wire retraction and droplet transfer through digital control;

[0010] Step 3: Keep the protective gas purging after welding is completed; after completion, first turn off the air compressor, laser, galvanometer controller, electric welder, Kuka robot, and finally turn off the water cooler and the power switch.

[0011] Furthermore, in the step 1, oil stains, oxide layers and impurities on the surface of the workpiece are removed by an angle grinder, and then the surface of the workpiece is cleaned with alcohol.

[0012] Furthermore, in the step 1, the workpiece used is a low-density high-strength aluminum alloy plate with a thickness of 3-5 mm and a composition range of: Mg: 0.4-1.5wt.%, Si: 0.2-1.2wt.%, Mn: 0.1-0.7wt.%, Fe≤0.7wt.%, Cu≤0.6wt.%, Zr≤0.1wt.%, Zn≤0.1wt.%, Cr≤0.1wt.%, Ti≤0.1wt. %, and the rest is Al. The welding wire used is aluminum-magnesium alloy welding wire with a diameter of 1-1.5mm. The brand is ER5356. The composition is: Mg: 4.5-5.5wt.%, Mn: 0.05-0.20wt.%, C: 0.05-0.20wt.%, Ti: 0.06-0.20wt.%, Fe≤0.40wt.%, Si≤0.25wt.%, Cu≤0.10wt.%, and the rest is Al.

[0013] Furthermore, in the step 1, when the workpiece is fixed to the welding fixture by a clamp, the assembly clearance is ensured to be ≤0.5 mm.

[0014] Furthermore, in step 2, the inert shielding gas introduced during welding is argon gas with a purity of ≥99.99%, a flow rate of 10-30 L / min, and an oxygen content controlled below 100 ppm.

[0015] Furthermore, in the step 2, when the laser head is not turned on for swinging, the distance between the light wires is 2-4 mm, and the angle between the laser head and the welding wire is 30-90°.

[0016] Furthermore, in step 2, the welding current of the CMT welder is 100-200A, the wire feeding speed is 9-10m / min, the laser power is 2.5-5KW, the welding speed is 0.02-0.04m / s, the laser beam swing frequency is 150-250Hz, and the swing amplitude is 1-2mm.

[0017] Furthermore, in step three, a wire brush is used to brush away dust and splashes on the surface of the weld.

[0018] The present invention has the following beneficial effects:

[0019] First, through the coupling regulation of laser high energy density and swing and CMT low heat input, the serious deformation, joint softening and thermal cracking caused by excessive heat input in the aluminum alloy welding process are effectively suppressed. At the same time, the cold metal transition characteristics of CMT are used to reduce the splashing of molten droplets, and the molten pool fluidity is improved by combining laser swing scanning, which significantly improves the quality of weld formation. Secondly, by optimizing the laser energy distribution, this method breaks through the limitation of aluminum alloy on the high reflectivity of laser, enhances the energy absorption efficiency, and solves the problems of low efficiency of traditional TIG welding and key hole defects in FSW while ensuring the welding speed. In practical application, compared with the conventional and currently used 6005A / 6A01 alloy profile, the melting welding coefficient is only 0.6, and the strength of the new low-density aluminum alloy base material is also far higher than that of ordinary 6XXX aluminum alloy, which is as high as 400MPa. The joint coefficient of the laser-CMT composite welding method of the present invention reaches 0.8, and the general performance is higher than the existing 6XXX aluminum alloy, which meets the high-precision welding requirements of lightweight structures of rail transit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of welding equipment;

[0021] Figure 2 It is the weld bead macroscopic morphology;

[0022] Figure 3 It is a curve chart of tensile property test results;

[0023] Figure 4 This is a microscopic morphology of the weld of Comparative Example 1;

[0024] Figure 5 This is a microscopic morphology of the weld in Example 1;

[0025] Figure 6 This is the microscopic morphology of the weld in comparative example 2;

[0026] Figure 7 This is a microscopic morphology of the weld in Example 2;

[0027] Figure 8 This is the microscopic morphology of the weld in comparative example 3;

[0028] Fig. 9 This is the microscopic morphology of the weld in Example 3. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] All the embodiments and comparative examples were carried out using the following steps:

[0031] Step 1: Preparation before welding

[0032] Turn on the power switch, and then turn on the water cooler, laser, galvanometer controller, electric welder, and Kuka robot in turn; install the welding wire to be used on the electric welder, then install the laser head and CMT welding gun and rigidly fix them with the clamp, and check the laser protection lens; use an angle grinder to grind off the oil, oxide layer and impurities on the surface of the workpiece, which is a low-density and high-strength aluminum alloy plate, and then clean the surface of the workpiece with alcohol; then fix the workpiece to the welding fixture.

[0033] Step 2: Welding process control

[0034] Preset basic parameters, including laser power, laser swing amplitude, laser swing frequency, defocus, CMT arc current, wire feeding speed, and set welding speed and shielding gas flow rate; select welding program, set welding start and end points, and then reset the program; turn on the air compressor and shielding gas cylinder, then turn on the laser galvanometer. During welding, the laser adopts arc swing mode, and finally set the automatic welding mode on the operating handle; when welding starts, trigger the laser first to focus the laser beam on the area to be welded, start the CMT welder synchronously, and coordinate wire retraction and droplet transition through digital control to reduce arc splashing. Ensure uniform weld formation.

[0035] Step 3: Post-welding treatment

[0036] After welding, keep the protective gas purging; use a wire brush to brush away dust and splashes on the weld surface; after finishing, turn off the air compressor, laser, galvanometer controller, electric welder, and Kuka robot first, and be sure to turn off the water cooler and the power switch last.

[0037] Specific embodiment 1: This embodiment is a new low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT. The specific composition of the workpiece used is: Mg: 0.95wt.%, Si: 1wt.%, Mn: 0.58wt.%, Fe: 0.15wt.%, Cu: 0.59wt.%, Zr: 0.15wt.%, Zn: 0.17wt.%, Cr: 0.033wt.%, Ti: 0.026wt.%, and the rest is Al. The aluminum-magnesium alloy welding wire used has a diameter of 1.2mm, the brand is ER5356, and the composition is: Mg: 4.9wt.%, Si: 0.13wt.%, Fe: 0.12wt.%, Cu: 0.0.1wt.%, Mn: 0.05wt.%, Cr: 0.07wt.%, Zn: 0.13wt.%, Ti: 0.11wt.%, and the remainder is Al.

[0038] In Example 1, when the workpiece is fixed to the welding fixture by a clamp, the assembly gap is ensured to be ≤0.5mm; during the welding process, an inert protective gas is introduced, the purity of argon is ≥99.99%, the flow rate is 25L / min, and the oxygen content is controlled below 100ppm; when the laser head is not turned on for swinging, the filament spacing is 3mm, and the angle between the laser head and the welding wire is 60°; the welding current of the CMT welding machine is 150A, the wire feeding speed is 9m / min, the laser power is 2.8KW, the welding speed is 0.03m / s, the laser beam swing frequency is 200Hz, and the swing amplitude is 1.5mm.

[0039] The low-density aluminum alloy weld strength prepared in Example 1 reaches 340.12 MPa, and the joint coefficient reaches 0.8. Through the coupling control of laser high energy density and swing and CMT low heat input, the joint softening and thermal cracking problems caused by excessive heat input during aluminum alloy welding are effectively suppressed. At the same time, the cold metal transition characteristics of CMT are used to reduce molten droplet splashing, and the fluidity of the molten pool is improved in combination with laser swing scanning, which significantly improves the weld forming quality.

[0040] Example 2: This example is a new low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT. The specific composition of the workpiece is: Mg: 0.95wt.%, Si: 1wt.%, Mn: 0.58wt.%, Fe: 0.15wt.%, Cu: 0.59wt.%, Zr: 0.15wt.%, Zn: 0.17wt.%, Cr: 0.033wt.%, Ti: 0.026wt.%, and the rest is Al. The aluminum-magnesium alloy welding wire used has a diameter of 1.2mm and a brand of ER5356. The composition is: Mg: 4.9wt.%, Si: 0.13wt.%, Fe: 0.12wt.%, Cu: 0.0.1wt.%, Mn: 0.05wt.%, Cr: 0.07wt.%, Zn: 0.13wt.%, Ti: 0.11wt.%, and the remainder is Al.

[0041] In Example 2, when the workpiece is fixed to the welding fixture by a clamp, the assembly gap is ensured to be ≤0.5mm; during the welding process, an inert protective gas is introduced, the purity of argon is ≥99.99%, the flow rate is 25L / min, and the oxygen content is controlled below 100ppm; when the laser head is not turned on for swinging, the filament spacing is 3mm, and the angle between the laser head and the welding wire is 60°; the welding current of the CMT welding machine is 150A, the wire feeding speed is 9.3m / min, the laser power is 3.6KW, the welding speed is 0.03m / s, the laser beam swing frequency is 200Hz, and the swing amplitude is 1.5mm.

[0042] The weld strength of the low-density aluminum alloy prepared in Example 2 reaches 309.47 MPa, and the joint coefficient reaches 0.74. This example reduces the laser power, which reduces the penetration depth, increases the weld width, increases the weld defects, and reduces the performance, but is still higher than the average level.

[0043] Example 3: This example is a new low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT. The specific composition of the workpiece is: Mg: 0.95wt.%, Si: 1wt.%, Mn: 0.58wt.%, Fe: 0.15wt.%, Cu: 0.59wt.%, Zr: 0.15wt.%, Zn: 0.17wt.%, Cr: 0.033wt.%, Ti: 0.026wt.%, and the rest is Al. The aluminum-magnesium alloy welding wire used has a diameter of 1-1.5mm, and the brand is ER5356. The composition is: Mg: 4.9wt.%, Si: 0.13wt.%, Fe: 0.12wt.%, Cu: 0.0.1wt.%, Mn: 0.05wt.%, Cr: 0.07wt.%, Zn: 0.13wt.%, Ti: 0.11wt.%, and the remainder is Al.

[0044] In Example 3, when the workpiece is fixed to the welding fixture by a clamp, the assembly gap is ensured to be ≤0.5mm; during the welding process, an inert protective gas is introduced, the purity of argon is ≥99.99%, the flow rate is 25L / min, and the oxygen content is controlled below 100ppm; when the laser head is not turned on for swinging, the filament spacing is 3mm, and the angle between the laser head and the welding wire is 60°; the welding current of the CMT welding machine is 150A, the wire feeding speed is 9.3m / min, the laser power is 4.4KW, the welding speed is 0.03m / s, the laser beam swing frequency is 200Hz, and the swing amplitude is 1.5mm.

[0045] The low-density aluminum alloy weld strength prepared in Example 3 reaches 290.82 MPa, and the joint coefficient reaches 0.69.

[0046] Comparative Example 1: This comparative example is a traditional laser-MIG composite welding method. The specific composition of the workpiece is: Mg: 0.95wt.%, Si: 1wt.%, Mn: 0.58wt.%, Fe: 0.15wt.%, Cu: 0.59wt.%, Zr: 0.15wt.%, Zn: 0.17wt.%, Cr: 0.033wt.%, Ti: 0.026wt.%, and the rest is Al. The aluminum-magnesium alloy welding wire used has a diameter of 1-1.5mm, a brand of ER5356, and a composition of: Mg: 4.9wt.%, Si: 0.13wt.%, Fe: 0.12wt.%, Cu: 0.0.1wt.%, Mn: 0.05wt.%, Cr: 0.07wt.%, Zn: 0.13wt.%, Ti: 0.11wt.%, and the remainder is Al.

[0047] In Comparative Example 1, when the workpiece is fixed to the welding fixture by a clamp, the assembly gap is ensured to be ≤0.5mm; during the welding process, an inert protective gas is introduced, the argon purity is ≥99.99%, the flow rate is 25L / min, and the oxygen content is controlled below 100ppm; when the laser head is not turned on and swung, the light wire spacing is 3mm, and the angle between the laser head and the welding wire is 60°; the welding current of the welding machine is 150A, the wire feeding speed is 9.3m / min, the laser power is 2.8KW, and the welding speed is 0.03m / s.

[0048] The weld strength of the low-density aluminum alloy prepared in Comparative Example 1 is 204.21 MPa, and the joint coefficient is only 0.49. This is because the molten pool is not stirred enough and the amount of pores increases when there is no laser oscillation. Without the dynamic regulation of CMT cold metal transition, the molten pool has poor fluidity, centerline cracks are easily formed, and the incidence of hot cracks increases.

[0049] Comparative Example 2: This comparative example is a new low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT. The specific composition of the workpiece is: Mg: 0.95wt.%, Si: 1wt.%, Mn: 0.58wt.%, Fe: 0.15wt.%, Cu: 0.59wt.%, Zr: 0.15wt.%, Zn: 0.17wt.%, Cr: 0.033wt.%, Ti: 0.026wt.%, and the rest is Al. The aluminum-magnesium alloy welding wire used has a diameter of 1-1.5mm, and the brand is ER5356. The composition is: Mg: 4.9wt.%, Si: 0.13wt.%, Fe: 0.12wt.%, Cu: 0.0.1wt.%, Mn: 0.05wt.%, Cr: 0.07wt.%, Zn: 0.13wt.%, Ti: 0.11wt.%, and the remainder is Al.

[0050] In Comparative Example 2, when the workpiece is fixed to the welding fixture by a clamp, the assembly gap is ensured to be ≤0.5mm; during the welding process, an inert protective gas is introduced, the purity of argon is ≥99.99%, the flow rate is 25L / min, and the oxygen content is controlled below 100ppm; when the laser head is not turned on for swinging, the filament spacing is 3mm, and the angle between the laser head and the welding wire is 60°; the welding current of the CMT welding machine is 150A, the wire feeding speed is 9.3m / min, the laser power is 3.2KW, the welding speed is 0.03m / s, the laser beam swing frequency is 200Hz, and the swing amplitude is 1.5mm.

[0051] The low-density aluminum alloy weld strength prepared in Comparative Example 2 reaches 280.39 MPa, and the joint coefficient reaches 0.67.

[0052] Comparative Example 3: This comparative example is a new low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT. The specific composition of the workpiece is: Mg: 0.95wt.%, Si: 1wt.%, Mn: 0.58wt.%, Fe: 0.15wt.%, Cu: 0.59wt.%, Zr: 0.15wt.%, Zn: 0.17wt.%, Cr: 0.033wt.%, Ti: 0.026wt.%, and the rest is Al. The aluminum-magnesium alloy welding wire used has a diameter of 1-1.5mm, and the brand is ER5356. The composition is: Mg: 4.9wt.%, Si: 0.13wt.%, Fe: 0.12wt.%, Cu: 0.0.1wt.%, Mn: 0.05wt.%, Cr: 0.07wt.%, Zn: 0.13wt.%, Ti: 0.11wt.%, and the remainder is Al.

[0053] In Comparative Example 3, when the workpiece is fixed to the welding fixture by a clamp, the assembly gap is ensured to be ≤0.5mm; during the welding process, an inert protective gas is introduced, the purity of argon is ≥99.99%, the flow rate is 25L / min, and the oxygen content is controlled below 100ppm; when the laser head is not turned on for swinging, the filament spacing is 3mm, and the angle between the laser head and the welding wire is 60°; the welding current of the CMT welding machine is 150A, the wire feeding speed is 9.3m / min, the laser power is 4KW, the welding speed is 0.03m / s, the laser beam swing frequency is 200Hz, and the swing amplitude is 1.5mm.

[0054] The low-density aluminum alloy weld strength prepared in Comparative Example 3 reaches 297.98 MPa, and the joint coefficient reaches 0.71.

[0055] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT, characterized in that: The following steps are involved: Step 1: Turn on the power switch, and then turn on the water cooler, laser, galvanometer controller, welder, and KUKA robot. Install the welding wire to the welder, then install the laser head and CMT welding gun and fix them rigidly with the fixture, and check the laser protection lens. Then fix the workpiece to the welding fixture. Step 2: Preset basic parameters, including laser power, laser oscillation amplitude, laser oscillation frequency, defocusing amount, CMT arc current, wire feeding speed, and set welding speed and shielding gas flow rate; select welding program, set welding start and end points, and then reset the program; turn on the air compressor and shielding gas cylinder, and then turn on the laser galvanometer. During welding, the laser adopts arc oscillation mode, and finally set the automatic welding mode on the operating handle; when welding starts, trigger the laser first to focus the laser beam on the area to be welded, start the CMT welder synchronously, and coordinate the wire retraction and droplet transfer through digital control; Step 3: Keep the protective gas purging after welding is completed; after completion, first turn off the air compressor, laser, galvanometer controller, electric welder, Kuka robot, and finally turn off the water cooler and the power switch.

2. According to claim 1, a novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT is characterized in that: In step 1, the oil, oxide layer and impurities on the surface of the workpiece are removed by an angle grinder, and then the surface of the workpiece is cleaned with alcohol.

3. The novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT according to claim 1 is characterized in that: In step three, use a wire brush to remove dust and spatter from the weld surface.

4. The novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT according to claim 1 is characterized in that: The workpiece used is a low-density, high-strength aluminum alloy plate with a thickness of 3-5 mm and a composition range of: Mg: 0.4-1.5wt.%, Si: 0.2-1.2wt.%, Mn: 0.1-0.7wt.%, Fe≤0.7wt.%, Cu≤0.6wt.%, Zr≤0.1wt.%, Zn≤0.1wt.%, Cr≤0.1wt.%, Ti≤0.1wt.%, and the rest is A 1. The welding wire used is aluminum-magnesium alloy welding wire with a diameter of 1-1.5mm, brand ER5356, and the composition is: Mg: 4.5-5.5wt.%, Mn: 0.05-0.20wt.%, C: 0.05-0.20wt.%, Ti: 0.06-0.20wt.%, Fe≤0.40wt.%, Si≤0.25wt.%, Cu≤0.10wt.%, and the rest is Al.

5. The novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT according to claim 1 is characterized in that: When the workpiece is fixed to the welding fixture through a clamp, the assembly clearance is ≤0.5mm.

6. The novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT according to claim 1 is characterized in that: During the welding process, an inert protective gas is introduced, the purity of argon is ≥99.99%, the flow rate is 10-30L / min, and the oxygen content is less than 100ppm.

7. The novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT according to claim 1 is characterized in that: When the laser head is not turned on for swinging, the distance between the light wires is 2-4mm, and the angle between the laser head and the welding wire is 30-90°.

8. The novel low-density and high-strength aluminum alloy composite welding method based on oscillating laser-CMT according to claim 1 is characterized in that: The welding current of CMT welding machine is 100-200A, the wire feeding speed is 9-10m / min, the laser power is 2.5-5KW, the welding speed is 0.02-0.04m / s, the laser beam swing frequency is 150-250Hz, and the swing amplitude is 1-2mm.

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