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

Abstract

The application discloses a kind of based on swing laser-CMT low-density high-strength aluminum alloy composite welding method, to solve the welding problem of high-strength low-density aluminum alloy in rail transit field.The application realizes the accurate control of welding heat input by the coupling effect of laser high energy density and CMT low heat input, and the specific method includes: presetting laser head swing frequency, amplitude and path control periodic swing of laser beam, setting CMT welder welding current, wire feeding speed, combined with optimized laser power, welding speed, reduce temperature gradient and thermal stress in the welding process.The joint strength of the low-density aluminum alloy welded by the application reaches 340.12MPa, and the joint coefficient reaches 0.8, which provides technical support for the lightweight and high performance of rail transit.

Description

TECHNICAL FIELD

[0001] The application relates to a low-density high-strength aluminum alloy composite welding method based on swing laser-CMT, and belongs to the technical field of laser welding. BACKGROUND

[0002] Under the demand of light weight of high-speed trains, low-density high-strength aluminum alloy has become a key basic material supporting the development of strategic emerging industries such as transportation field, high-end equipment manufacturing industry and new materials. However, with the breakthrough improvement of the material strength level, the welding thermodynamic characteristics and solidification behavior change significantly, resulting in interface mismatch phenomena such as joint softening and intergranular segregation under the conventional welding process, 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 the following types according to the heat source type: gas metal arc welding (MIG), gas tungsten arc welding (TIG), friction stir welding (FSW) and laser beam welding. Because the MIG arc energy density is low and not concentrated, a large heat input is needed during welding, which is easy to cause large welding deformation, serious joint softening and many thermal cracks; the arc is stable during TIG welding, and the weld is beautiful and not easy to produce spatter, however, the welding speed is slow and the penetration is shallow, and the welding efficiency is low, which is difficult to weld thick plates; in the friction stir welding, the base material does not melt, so it does not need protection gas, which can reduce the occurrence of pores and cracks to a certain extent. However, the welding speed is limited, a key hole is formed at the end of the weld due to the stirring probe, which is difficult to repair, and a large upset force is needed, which is not suitable for welding of complex structures. When aluminum alloy is welded by adding a laser beam, the high power density of the laser can be used for welding in a short time, improving the welding efficiency and obtaining a more beautiful weld. However, the following defects may occur during welding: hydrogen pores and process pores are generated due to the hydrogen gas generated in the molten pool; thermal cracks with large welding stress and welding deformation are caused due to the high shrinkage rate of aluminum alloy during solidification; the reflectivity of aluminum alloy to laser photons is high, resulting in insufficient absorption of laser.

[0004] Therefore, it is urgent to provide a low-density high-strength aluminum alloy composite welding method to solve the above technical problems. SUMMARY

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

[0006] In view of the joint softening, pores and thermal cracks caused by excessive heat input in the welding of high-strength aluminum alloy, a low-density high-strength aluminum alloy composite welding method based on swing laser-CMT (cold metal transition welding) is provided.

[0007] The technical scheme of the application is:

[0008] Step one: open the electric switch, in turn, open the water cooling machine, laser, galvanometer controller, electric welder, Kuka robot; the welding wire is installed on the electric welder, then the laser head and CMT welding gun are installed and fixed rigidly through the clamp, and the laser protection lens is checked; then the workpiece is fixed on the welding fixture clamp;

[0009] Step two: preset the basic parameters, including laser power, laser swing amplitude, laser swing frequency, defocusing amount, and CMT arc current, wire feeding speed, welding speed and protective gas flow are set at the same time; select the welding program, set the welding starting point and ending point, then reset the program; open the air compressor and the protective gas cylinder, then start the laser galvanometer, during the welding process, the laser adopts a circular arc swing mode, finally set the automatic welding mode on the handle; when the welding starts, the laser is triggered first, the laser beam is focused on the welding area, the CMT welder is started synchronously, and the coordination of wire withdrawal and droplet transition is realized through digital control;

[0010] Step three: after the welding is completed, the protective gas is blown; after the end, the air compressor, laser, galvanometer controller, electric welder, Kuka robot are closed first, and finally the water cooling machine is closed, and the electric switch is closed.

[0011] Further, in step one, the oil stains, oxidation 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.

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

[0013] Further, in step one, when the workpiece is fixed on the welding fixture clamp through the clamp, the assembly gap is ensured to be ≤0.5 mm.

[0014] Further, in the step two, the inert protective gas in the welding process is argon, the purity is greater than or equal to 99.99%, the flow rate is 10-30 L / min, and the oxygen content is controlled to be less than 100 ppm.

[0015] Further, in the step two, the light wire spacing is 2-4 mm under the condition that the laser head does not swing, and the laser head and the welding wire are at an angle of 30-90 degrees.

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

[0017] Further, in the step three, the dust and spatter on the surface of the weld are brushed away by using a steel wire brush.

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

[0019] Firstly, by coupling regulation of laser high energy density and swing and CMT low heat input, the problems of serious deformation, joint softening and thermal cracking caused by excessive heat input in the aluminum alloy welding process are effectively inhibited, the cold metal transfer characteristics of CMT are used to reduce the droplet spatter, the laser swing scanning is combined to improve the fluidity of the molten pool, and the weld forming quality is significantly improved. Secondly, by optimizing the laser energy distribution, the limitation of high reflectivity of aluminum alloy on laser is broken, and the energy absorption efficiency is enhanced, so that the welding speed is ensured, and the problems of low efficiency of traditional TIG welding and key hole defects of FSW are solved. In the actual application level, compared with the conventional and existing 6005A / 6A01 alloy profile melting welding coefficient of only 0.6, the strength of the low-density aluminum alloy base material is also much higher than that of ordinary 6XXX aluminum alloy, which is as high as 400 MPa. The joint coefficient of the laser-CMT composite welding method of the present application reaches 0.8, and the general performance is higher than that of the existing 6XXX aluminum alloy, which meets the high-precision welding requirements of the lightweight structure of the rail transit. BRIEF DESCRIPTION OF DRAWINGS

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

[0021] Figure 2 is a macroscopic morphology diagram of a weld;

[0022] Figure 3 is a tensile property test result curve diagram;

[0023] Figure 4 is a microscopic morphology diagram of the weld of the comparative example 1;

[0024] Figure 5is a weld micrograph of Example 1;

[0025] Figure 6 is a weld micrograph of Comparative Example 2;

[0026] Figure 7 is a weld micrograph of Example 2;

[0027] Figure 8 is a weld micrograph of Comparative Example 3;

[0028] Figure 9 is a weld micrograph of Example 3. DETAILED DESCRIPTION

[0029] In order to make the person skilled in the art better understand the technical scheme of the present application, the technical scheme of the present application will be further explained below in combination with the drawings and specific examples.

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

[0031] Step one: preparation before welding

[0032] Turn on the power switch, and then turn on the water chiller, laser, galvanometer controller, electric welder, and Kuka robot in sequence. Install the welding wire on the electric welder, and then install the laser head and CMT welding gun and rigidly fix them through the clamp. Check the laser protective lens. Grind off the oil stains, oxidation layer, and impurities on the surface of the workpiece, i.e., the low-density high-strength aluminum alloy plate, using an angle grinder, and then clean the surface of the workpiece with alcohol. Then fix the workpiece on the welding fixture clamp.

[0033] Step two: welding process control

[0034] Pre-set the basic parameters, including laser power, laser swing amplitude, laser swing frequency, defocusing amount, CMT arc current, wire feeding speed, welding speed, and protective gas flow. Select the welding program, set the welding starting point and ending point, and then reset the program. Turn on the air compressor and protective gas cylinder, and then turn on the laser galvanometer. During the welding process, the laser adopts a circular arc swing mode. Finally, set the automatic welding mode on the operating handle. When the welding starts, first trigger the laser, so that the laser beam is focused on the area to be welded. Simultaneously, start the CMT welder and realize the coordination of wire withdrawal and droplet transfer through digital control, so as to reduce the arc striking spatter. Ensure that the weld is uniformly formed.

[0035] Step three: post-welding treatment

[0036] After the welding is completed, keep the protective gas blowing. Use a steel wire brush to brush off the dust and spatter on the surface of the weld. After the end, first turn off the air compressor, laser, galvanometer controller, electric welder, and Kuka robot. Finally, turn off the water chiller and power switch.

[0037] Specific embodiment 1: this embodiment is a low-density high-strength aluminum alloy composite welding method based on swing laser-CMT, the specific composition of the workpiece used is: Mg: 0.95 wt.%, Si: 1 wt.%, Mn: 0.58 wt.%, Fe: 0.15 wt.%, Cu: 0.59 wt.%, Zr: 0.15 wt.%, Zn: 0.17 wt.%, Cr: 0.033 wt.%, Ti: 0.026 wt.%, the rest is Al, the aluminum magnesium alloy welding wire used has a diameter of 1.2 mm and a brand of ER5356, and the composition is: Mg: 4.9 wt.%, Si: 0.13 wt.%, Fe: 0.12 wt.%, Cu: 0.1 wt.%, Mn: 0.05 wt.%, Cr: 0.07 wt.%, Zn: 0.13 wt.%, Ti: 0.11 wt.%, and the balance is Al.

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

[0039] The low-density aluminum alloy weld prepared in example 1 has a strength of 340.12 MPa, and the joint coefficient reaches 0.8. Through the coupling regulation of high energy density of laser and swing and low heat input of CMT, the joint softening and thermal cracking problems caused by excessive heat input during aluminum alloy welding are effectively inhibited, the cold metal transfer characteristics of CMT are used to reduce the spatter of molten droplets, the laser swing scanning is combined to improve the fluidity of the molten pool, and the weld forming quality is significantly improved.

[0040] Embodiment 2: The embodiment is a low-density high-strength aluminum alloy composite welding method based on swing laser-CMT. The specific composition of the workpiece is: Mg: 0.95 wt.%, Si: 1 wt.%, Mn: 0.58 wt.%, Fe: 0.15 wt.%, Cu: 0.59 wt.%, Zr: 0.15 wt.%, Zn: 0.17 wt.%, Cr: 0.033 wt.%, Ti: 0.026 wt.%, and the rest is Al. The aluminum magnesium alloy welding wire used has a diameter of 1.2 mm and a brand of ER5356, and the composition is: Mg: 4.9 wt.%, Si: 0.13 wt.%, Fe: 0.12 wt.%, Cu: 0.1 wt.%, Mn: 0.05 wt.%, Cr: 0.07 wt.%, Zn: 0.13 wt.%, Ti: 0.11 wt.%, and the balance is Al.

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

[0042] The weld strength of the low-density aluminum alloy prepared in embodiment 2 reaches 309.47 MPa, and the joint coefficient reaches 0.74. In this embodiment, the laser power is reduced, the penetration depth is reduced, the weld width is increased, the weld defects are increased, and the performance is decreased, but it is still higher than the average level.

[0043] Embodiment 3: The embodiment is a low-density high-strength aluminum alloy composite welding method based on swing laser-CMT. The specific composition of the workpiece is: Mg: 0.95 wt.%, Si: 1 wt.%, Mn: 0.58 wt.%, Fe: 0.15 wt.%, Cu: 0.59 wt.%, Zr: 0.15 wt.%, Zn: 0.17 wt.%, Cr: 0.033 wt.%, Ti: 0.026 wt.%, and the rest is Al. The aluminum magnesium alloy welding wire used has a diameter of 1-1.5 mm and a brand of ER5356, and the composition is: Mg: 4.9 wt.%, Si: 0.13 wt.%, Fe: 0.12 wt.%, Cu: 0.1 wt.%, Mn: 0.05 wt.%, Cr: 0.07 wt.%, Zn: 0.13 wt.%, Ti: 0.11 wt.%, and the balance is Al.

[0044] In Example 3, the workpiece is fixed to the welding fixture by the clamp, and the assembly gap is ensured to be less than or equal to 0.5 mm; inert protective gas is introduced during the welding process, the purity of argon is greater than or equal to 99.99%, the flow rate is 25 L / min, and the oxygen content is controlled to be less than 100 ppm; the light wire spacing is 3 mm, and the laser head and the welding wire form an angle of 60°; the CMT welding machine welding current is 150 A, the wire feeding speed is 9.3 m / min, the laser power is 4.4 KW, the welding speed is 0.03 m / s, the laser beam oscillation frequency is 200 Hz, and the oscillation amplitude is 1.5 mm.

[0045] The weld strength of the low-density aluminum alloy 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 hybrid welding method. The workpiece has the following specific components: Mg: 0.95 wt.%, Si: 1 wt.%, Mn: 0.58 wt.%, Fe: 0.15 wt.%, Cu: 0.59 wt.%, Zr: 0.15 wt.%, Zn: 0.17 wt.%, Cr: 0.033 wt.%, Ti: 0.026 wt.%, and the rest is Al. The aluminum magnesium alloy welding wire used has a diameter of 1-1.5 mm and a brand of ER5356, and has the following components: Mg: 4.9 wt.%, Si: 0.13 wt.%, Fe: 0.12 wt.%, Cu: 0.1 wt.%, Mn: 0.05 wt.%, Cr: 0.07 wt.%, Zn: 0.13 wt.%, Ti: 0.11 wt.%, and the rest is Al.

[0047] In Comparative Example 1, the workpiece is fixed to the welding fixture by the clamp, and the assembly gap is ensured to be less than or equal to 0.5 mm; inert protective gas is introduced during the welding process, the purity of argon is greater than or equal to 99.99%, the flow rate is 25 L / min, and the oxygen content is controlled to be less than 100 ppm; the light wire spacing is 3 mm, and the laser head and the welding wire form an angle of 60°; the welding machine welding current is 150 A, the wire feeding speed is 9.3 m / min, the laser power is 2.8 KW, and the welding speed is 0.03 m / 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, which is due to the lack of laser oscillation, insufficient stirring of the molten pool, and increased gas hole precipitation. Without the dynamic regulation of CMT cold metal transition, the molten pool has poor fluidity, is prone to form centerline cracks, and the incidence of hot cracks increases.

[0049] Comparative Example 2: This comparative example is a low-density high-strength aluminum alloy composite welding method based on swing laser-CMT. The workpiece has the following composition: Mg: 0.95 wt.%, Si: 1 wt.%, Mn: 0.58 wt.%, Fe: 0.15 wt.%, Cu: 0.59 wt.%, Zr: 0.15 wt.%, Zn: 0.17 wt.%, Cr: 0.033 wt.%, Ti: 0.026 wt.%, and the balance being Al. The aluminum magnesium alloy wire used has a diameter of 1-1.5 mm and a brand of ER5356, and has the following composition: Mg: 4.9 wt.%, Si: 0.13 wt.%, Fe: 0.12 wt.%, Cu: 0.1 wt.%, Mn: 0.05 wt.%, Cr: 0.07 wt.%, Zn: 0.13 wt.%, Ti: 0.11 wt.%, and the balance being Al.

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

[0051] The weld strength of the low-density aluminum alloy 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 low-density high-strength aluminum alloy composite welding method based on swing laser-CMT. The workpiece has the following composition: Mg: 0.95 wt.%, Si: 1 wt.%, Mn: 0.58 wt.%, Fe: 0.15 wt.%, Cu: 0.59 wt.%, Zr: 0.15 wt.%, Zn: 0.17 wt.%, Cr: 0.033 wt.%, Ti: 0.026 wt.%, and the balance being Al. The aluminum magnesium alloy wire used has a diameter of 1-1.5 mm and a brand of ER5356, and has the following composition: Mg: 4.9 wt.%, Si: 0.13 wt.%, Fe: 0.12 wt.%, Cu: 0.1 wt.%, Mn: 0.05 wt.%, Cr: 0.07 wt.%, Zn: 0.13 wt.%, Ti: 0.11 wt.%, and the balance being Al.

[0053] In the comparative example 3, the workpiece is fixed on the welding tooling fixture by the clamp, and the assembly gap is ensured to be less than or equal to 0.5 mm; inert protective gas is introduced during the welding process, the purity of argon is greater than or equal to 99.99%, the flow rate is 25 L / min, the oxygen content is controlled to be less than or equal to 100 ppm; the light wire spacing is 3 mm under the condition that the laser head does not swing, the angle between the laser head and the welding wire is 60°; the CMT welding machine welding current is 150 A, the wire feeding speed is 9.3 m / min, the laser power is 4 KW, the welding speed is 0.03 m / s, the laser beam swing frequency is 200 Hz, and the swing amplitude is 1.5 mm.

[0054] The low-density aluminum alloy weld joint prepared in the comparative example 3 has a strength of 297.98 MPa, and the joint coefficient is 0.71.

[0055] The above has exemplarily described the present application, and it should be indicated that, without departing from the core of the present application, any simple transformation, modification or other equivalent replacement which can not cost creative labor of the person skilled in the art falls into the protection scope of the present application.

Claims

1. A low-density high-strength aluminum alloy composite welding method based on swing laser-CMT, characterized in that, The method comprises the following steps: Step one: open the electric switch, and sequentially open the water cooling machine, laser, galvanometer controller, electric welder, and Kuka robot; install the welding wire on the electric welder, then install the laser head and CMT welding gun and rigidly fix them through the clamp, and check the laser protection lens; then fix the workpiece on the welding fixture clamp; Step two: preset the basic parameters, including laser power, laser swing amplitude, laser swing frequency, defocusing amount, CMT arc current, wire feeding speed, welding speed, and shielding gas flow; select the welding program, set the welding starting point and ending point, and then reset the program; open the air compressor and shielding gas cylinder, then open the laser galvanometer; during the welding process, the laser adopts a circular arc swing mode; finally, set the automatic welding mode on the operating handle; when the welding starts, first trigger the laser, so that the laser beam focuses on the to-be-welded area; simultaneously start the CMT welder and realize the coordination of wire withdrawal and droplet transition through digital control; In the method, the CMT welder welding current is 100-200 A, the wire feeding speed is 9-10 m / min, the laser power is 2.5-5 KW, the welding speed is 0.02-0.04 m / s, the laser beam swing frequency is 150-250 Hz, and the swing amplitude is 1-2 mm; Step three: after the welding is completed, keep the shielding gas blowing; after the completion, first close the air compressor, laser, galvanometer controller, electric welder, and Kuka robot, and finally close the water cooling machine and electric switch.

2. The low-density high-strength aluminum alloy composite welding method based on swing laser-CMT according to claim 1, characterized in that: In step one, the oil stains, oxide layers, and impurities on the surface of the workpiece are removed through an angle grinder, and then the surface of the workpiece is cleaned with alcohol.

3. The low-density high-strength aluminum alloy composite welding method based on swing laser-CMT according to claim 1, characterized in that: In step three, the dust and splashes on the surface of the weld are brushed away with a steel wire brush.

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

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

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

7. The method of claim 1, wherein the method is a low-density high-strength aluminum alloy composite welding method based on a swing laser-CMT. Under the condition that the laser head does not swing, the light-wire spacing is 2-4 mm, and the angle between the laser head and the welding wire is 30-90°.

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