Magnesium alloy low-vacuum laser welding method for atmosphere regulation and control

Abstract

The invention discloses an atmosphere-controlled magnesium alloy low-vacuum laser welding method, and belongs to the technical field of laser welding. The problems that an existing traditional magnesium alloy welding seam is poor in forming and prone to oxidation, air holes are prone to being generated, and the quality of a welding joint is seriously affected are solved. The welding method comprises the following steps: 1, polishing and cleaning the to-be-welded surface of the magnesium alloy plate; 2, placing on a workbench; (3) vacuumizing; 4, introducing inert gas; and 5, welding. The method is used for atmosphere-controlled magnesium alloy low-vacuum laser welding.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of laser welding. BACKGROUND

[0002] Laser as a high energy density welding method, it has high efficiency, low heat input, precise heat affected zone control and flexibility and other significant advantages. Magnesium alloy belongs to eutectic alloy, has a large linear expansion coefficient, high thermal conductivity, large specific heat capacity, low melting point and other characteristics, in the use of traditional fusion welding method welding is prone to produce thermal cracks, porosity, alloy element burn loss and welding area softening and other problems. At the same time, magnesium alloy has high reflection, strong evaporation and other material properties, its intense molten pool behavior and unstable keyhole behavior make it produce hump, welding tumor, uneven cross section weld forming and porosity and other welding defects in the welding process. Its higher keyhole formation threshold also makes it difficult to form large depth of penetration. A high-efficiency and high-quality connection method is urgently needed to be applied to the welding of magnesium alloy thick plate to realize reliable connection of high quality.

[0003] In recent years, vacuum laser welding has gradually entered the field of view of researchers and has attracted much attention. A large amount of research work has been carried out on the influence of vacuum environment on laser welding, and some common understandings have been obtained. The vacuum environment can suppress the welding plume, reduce the laser scattering, and at the same time, it can reduce the boiling point and the energy threshold required for the formation of keyhole, greatly improving the welding depth. At the same time, there is a relatively stable molten pool and keyhole behavior in low vacuum environment, which to some extent improves some problems in the welding of metal thick plate.

[0004] However, as a material highly sensitive to oxygen, magnesium alloy will still be affected by the residual oxygen in the atmosphere even in a low vacuum environment. In the high-temperature welding process, the residual oxygen in the atmosphere will react violently with the molten pool, affecting the stability of the welding process. The fluctuation of the molten pool and the keyhole will cause poor weld forming quality and internal defects such as porosity, thereby affecting the mechanical properties of the joint. SUMMARY

[0005] The present application solves the problems of poor weld forming, easy oxidation and porosity in the existing traditional magnesium alloy welding, which seriously affects the quality of the welded joint, and further provides a magnesium alloy low vacuum laser welding method with atmosphere regulation.

[0006] A magnesium alloy low vacuum laser welding method with atmosphere regulation, which is carried out according to the following steps:

[0007] I. The surface to be welded of the magnesium alloy plate is polished and cleaned to obtain a magnesium alloy plate to be welded;

[0008] II. The magnesium alloy plate to be welded is placed on the workbench in the vacuum work cabin;

[0009] III. vacuumizing the vacuum working cabin to a limit vacuum degree;

[0010] IV. introducing inert gas into the vacuum working cabin to reach an ambient pressure of 5-30 kPa;

[0011] V. under the conditions of inert atmosphere, ambient pressure of 5-30 kPa, laser power of 3-8 kW, welding speed of 0.6-1.8 m / min, defocusing amount of -20-+10 mm and laser vertical incidence, laser surfacing is performed on the surface of the magnesium alloy plate to be welded according to the path, thereby completing the magnesium alloy low-vacuum laser welding method with atmosphere regulation.

[0012] The present application has the following advantages:

[0013] (1) The magnesium alloy low-vacuum laser welding method with atmosphere regulation of the present application can vacuumize the vacuum working cabin to a limit vacuum degree, introduce inert gas into the cabin to reach an ambient pressure suitable for magnesium alloy welding, combine with welding process parameters, generate welding laser through the laser and the laser head connected thereto, and make the welding laser perform welding operation according to preset parameters and path. This method is efficient and quick, and can obtain a welding joint with good weld forming and qualified quality.

[0014] (2) The magnesium alloy low-vacuum laser welding method with atmosphere regulation of the present application can effectively increase the weld penetration by welding in a vacuum environment. Laser welding in a vacuum environment can effectively avoid the periodic expansion and contraction of the keyhole, which often occurs in the atmospheric environment. Under low-vacuum conditions, the fluctuation amplitude of the rear wall of the keyhole is small, the stability is improved, and the keyhole collapse rarely occurs. Under low-vacuum conditions, the molten pool exists surface tension driven flow and upward flow along the rear wall of the keyhole. This flow pattern is beneficial to the escape of bubbles in the molten pool and is not easy to form pores in the welding joint.

[0015] (3) The magnesium alloy low-vacuum laser welding method with atmosphere regulation of the present application can solve the oxidation problem of magnesium alloy in a low-vacuum environment by further introducing inert gas to improve the welding atmosphere, and further improve the weld quality of magnesium alloy low-vacuum laser welding. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 FIG. 1 is a schematic diagram of the overall structure of the system used for the magnesium alloy low-vacuum laser welding method with atmosphere regulation in Example 1, wherein 1 is a laser, 2 is a laser head, 3 is a vacuum working cabin, 4 is a vacuum pump, 5 is a water cooling circulation mechanism, 6 is a workbench control unit, 7 is a vacuum control unit, 8 is a workbench, and 9 is an inert gas bottle.

[0017] Figure 2A low-vacuum welding surface forming diagram of the magnesium alloy in Example 1 and Comparative Examples 1-3;

[0018] Figure 3 A low-vacuum welding cross-section forming diagram of the magnesium alloy in Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0019] Specific embodiment one: the magnesium alloy low-vacuum laser welding method of the present embodiment is carried out according to the following steps:

[0020] I. The surface to be welded of the magnesium alloy plate is polished and cleaned to obtain the magnesium alloy plate to be welded;

[0021] II. The magnesium alloy plate to be welded is placed on the workbench in the vacuum work cabin;

[0022] III. The vacuum work cabin is evacuated to the limit vacuum degree;

[0023] IV. Inert gas is introduced into the vacuum work cabin to reach an environmental pressure of 5-30 kPa;

[0024] V. Under the conditions of inert atmosphere, environmental pressure of 5-30 kPa, laser power of 3-8 kW, welding speed of 0.6-1.8 m / min, defocusing amount of -20-+10 mm, and laser vertical incidence, the surface of the magnesium alloy plate to be welded is laser surfacing according to the path, i.e. a magnesium alloy low-vacuum laser welding method of atmosphere control is completed.

[0025] The beneficial effects of the present embodiment are:

[0026] (1) The magnesium alloy low-vacuum laser welding method of atmosphere control of the present embodiment evacuates the vacuum work cabin to the limit vacuum degree, introduces inert gas into the cabin to reach an environmental pressure suitable for magnesium alloy welding, combines with the welding process parameters, generates welding laser through the laser and the laser head connected thereto, and makes the welding laser perform welding operation according to the preset parameters and path. This method is efficient and quick, and can obtain a welding joint with good weld forming and qualified quality.

[0027] (2) The magnesium alloy low-vacuum laser welding method of atmosphere control of the present embodiment can effectively increase the weld penetration by welding in a vacuum environment; laser welding in a vacuum environment can effectively avoid the periodic expansion and contraction phenomenon of the keyhole which often occurs in the atmospheric environment. Under low-vacuum conditions, the fluctuation amplitude of the rear wall of the keyhole is small, the stability is improved, and the collapse of the keyhole rarely occurs; under low-vacuum conditions, there is surface tension driven flow in the molten pool and upward flow along the rear wall of the keyhole; this flow pattern is conducive to the escape of bubbles in the molten pool and is not easy to form pores in the welding joint.

[0028] (3) The atmosphere-controlled magnesium alloy low-vacuum laser welding method of the embodiment can solve the oxidation problem of the magnesium alloy in the low-vacuum environment by further introducing the inert gas to improve the welding atmosphere, and further improve the welding seam quality of the magnesium alloy low-vacuum laser welding.

[0029] Specific embodiment two: The magnesium alloy plate in step one is made of AZ31, AZ61 AZ91 or WE43. The rest is the same as specific embodiment one.

[0030] Specific embodiment three: The magnesium alloy plate in step one has a thickness of 5mm~25mm. The rest is the same as specific embodiment one or two.

[0031] Specific embodiment four: The limit vacuum degree in step three is 10 -2 kPa~10 -1 kPa. The rest is the same as specific embodiment one to three.

[0032] Specific embodiment five: In step four, the inert gas is introduced into the vacuum working chamber to reach an environmental pressure of 10kPa. The rest is the same as specific embodiment one to four.

[0033] Specific embodiment six: The inert gas in step four is argon or helium. The rest is the same as specific embodiment one to five.

[0034] Specific embodiment seven: The path in step five is a straight line path. The rest is the same as specific embodiment one to six.

[0035] Specific embodiment eight: In step five, a circular spot is used to laser build up welding on the magnesium alloy plate according to the path. The rest is the same as specific embodiment one to seven.

[0036] Specific embodiment nine: The spot diameter is 0.06mm~0.1mm. The rest is the same as specific embodiment one to eight.

[0037] Specific embodiment ten: The weld seam width formed after laser build up welding in step five is 1mm~3mm. The rest is the same as specific embodiment one to nine.

[0038] The beneficial effects of the present application are verified by the following examples:

[0039] Example 1:

[0040] A low-vacuum laser welding method for atmosphere-controlled magnesium alloy is carried out according to the following steps:

[0041] I. Using a sander, polish the surface to be welded of the magnesium alloy plate, then clean it with acetone using industrial silk, to obtain the magnesium alloy plate to be welded;

[0042] II. Place the magnesium alloy plate to be welded on the workbench in the vacuum work cabin;

[0043] III. Vacuum the vacuum work cabin to a limit vacuum degree of 10 kPa; -2

[0044] IV. Introduce inert gas into the vacuum work cabin to an environmental pressure of 10 kPa;

[0045] V. Under the conditions of inert atmosphere, an environmental pressure of 10 kPa, a laser power of 3 kW, a welding speed of 0.9 m / min, focusing, and vertical laser incidence, laser build-up welding is performed on the surface of the magnesium alloy plate to be welded according to the path, thereby completing a low-vacuum laser welding method for atmosphere-controlled magnesium alloy.

[0046] The magnesium alloy plate in step I has a material of AZ31.

[0047] The magnesium alloy plate in step I has a thickness of 20 mm.

[0048] The inert gas in step IV is argon.

[0049] The path in step V is a straight-line path.

[0050] In step V, a circular light spot is used to perform laser build-up welding on the magnesium alloy plate to be welded according to the path.

[0051] The light spot has a diameter of 0.08 mm.

[0052] The weld seam width formed after laser build-up welding in step V is 2 mm.

[0053] Comparative Example 1: The difference between this comparative example and Example 1 is that in step III, the vacuum work cabin is vacuumed to an environmental pressure of 10 kPa; step IV is cancelled. The rest is the same as Example 1.

[0054] ​Comparative Example 2: This comparative example differs from Example 1 in that: in step three, the vacuum working chamber is evacuated to an ambient pressure of 7 kPa; in step four, inert gas is introduced into the vacuum working chamber to achieve an ambient pressure of 10 kPa. Everything else is the same as in Example 1.

[0055] Comparative Example 3: This comparative example differs from Example 1 in that: in step three, the vacuum working chamber is evacuated to an ambient pressure of 4 kPa; in step four, inert gas is introduced into the vacuum working chamber to achieve an ambient pressure of 10 kPa. Everything else is the same as in Example 1.

[0056] Figure 1 This is a schematic diagram of the overall structure of the system used in the atmosphere-controlled low-vacuum laser welding method for magnesium alloys in Example 1. 1 is the laser, 2 is the laser head, 3 is the vacuum working chamber, 4 is the vacuum pump, 5 is the water-cooling circulation mechanism, 6 is the worktable control unit, 7 is the vacuum pump control unit, 8 is the worktable, and 9 is an inert gas cylinder. The output end of the laser 1 is connected to the laser head 2, and the output end of the laser head 2 is located inside the vacuum working chamber 3. The worktable 8 is located inside the vacuum working chamber 3. The vacuum working chamber 3 is connected to the vacuum pump 4, which is connected to the vacuum pump control unit 7. The worktable 8 is connected to the worktable control unit 6. Before welding, the surface of the magnesium alloy plate to be welded is ground and cleaned. The magnesium alloy plate is placed inside the vacuum working chamber 3. Magnesium alloy plate to be welded; the vacuum pumping control unit 7 controls the vacuum pumping mechanism 4 to perform vacuuming operations on the vacuum working chamber 3, so that it reaches the ultimate vacuum level that the equipment can achieve; inert gas argon is introduced into the vacuum working chamber 3 to achieve an environmental pressure suitable for magnesium alloy welding; the water cooling circulation mechanism 5 is turned on, the welding process parameters are set, and the welding laser is generated by the laser 1 and the laser head 2. The welding laser works according to the preset path and parameters; at the same time, the platform control unit 6 controls the worktable 8 to move along the main direction of the weld trajectory, thereby performing vacuum laser welding on the magnesium alloy plate to be welded; this embodiment can improve the welding atmosphere, solve the oxidation problem of magnesium alloy in a low vacuum environment, and further improve the weld quality of low vacuum laser welding of magnesium alloy.

[0057] Figure 2 The images show the surface formation of the magnesium alloy low-vacuum welds in Examples 1 and 3, respectively. The surface formation images of the welds under different degrees of inert gas atmosphere control show that in Comparative Examples 1, 2, and 3, the welds exhibited varying degrees of oxidation, poor surface continuity, and obvious hump defects, indicating poor weld quality. In contrast, the surface of Example 1 had a metallic luster, was smooth and continuous, and showed no obvious oxidation or hump defects.

[0058] Figure 3The cross-sectional shapes of the low-vacuum welds of magnesium alloys in Examples 1 and 1 to 3 are shown. The cross-sectional shapes of the welds under different degrees of inert gas atmosphere control show that some porosity defects can be found in Comparative Examples 1, 2 and 3. As the proportion of inert gas increases, the atmosphere is improved and the porosity defects are suppressed to a certain extent. No obvious porosity defects were found in Example 1, and the welds in the example still retain the characteristics of a large depth-to-width ratio.

[0059] The above comparison shows that low-vacuum laser welds with atmosphere controlled by inert gas have better surface formation and fewer porosity defects.

Claims

1. A method for low-vacuum laser welding of magnesium alloys with atmosphere control, characterized in that... It is done in the following steps:

1. Grind and clean the surface of the magnesium alloy sheet to be welded to obtain the magnesium alloy sheet to be welded; 2. Place the magnesium alloy plate to be welded on the worktable inside the vacuum working chamber; 3. Evacuate the vacuum working chamber to the ultimate vacuum level; 4. Inert gas is introduced into the vacuum working chamber to achieve an ambient pressure of 5 kPa to 30 kPa; V. Under the conditions of an inert atmosphere, an ambient pressure of 5kPa~30kPa, a laser power of 3kW~8kW, a welding speed of 0.6m / min~1.8m / min, a defocusing amount of -20mm to +10mm, and perpendicular laser incidence, laser cladding is performed on the surface of the magnesium alloy plate to be welded according to the path, thus completing an atmosphere-controlled low-vacuum laser welding method for magnesium alloys.

2. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... The magnesium alloy sheet material mentioned in step one is AZ31, AZ61, AZ91 or WE43.

3. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... The thickness of the magnesium alloy sheet mentioned in step one is 5mm to 25mm.

4. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... The ultimate vacuum degree mentioned in step three is 10. -2 kPa~10 -1 kPa.

5. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... In step four, inert gas is introduced into the vacuum working chamber to achieve an ambient pressure of 10 kPa.

6. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... The inert gas mentioned in step four is argon or helium.

7. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... The path described in step five is a straight path.

8. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... In step five, a circular laser spot is used to perform laser welding on the magnesium alloy plate to be welded, following the path.

9. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 8, characterized in that... The diameter of the light spot is 0.06mm to 0.1mm.

10. The method for low-vacuum laser welding of magnesium alloys with atmosphere control according to claim 1, characterized in that... The width of the weld formed after laser welding in step five is 1mm to 3mm.

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