An apparatus and method for reducing element burn-off in laser welded magnesium-lithium alloy welds

Abstract

The application relates to the field of welding technology, and specifically discloses a device and method for reducing element burning loss of a magnesium-lithium alloy laser welding seam, wherein the device comprises a base and a clamp, an upper end surface of the base is provided with a through groove, and a guide rail is arranged in the through groove in a lifting mode; a preheating rod is arranged on the guide rail in a sliding mode, the preheating rod comprises a rod body and a preheating end, extrusion mechanisms are arranged on the base on both sides of a base material, and an upper scraper and a lower scraper are arranged on the upper and lower sides of the welding seam in a sliding mode. The method comprises base material clamping, preheating before welding, laser welding, liquid metal extrusion and scraping and post-welding heat treatment. The lower surface of the butt joint of the base material is preheated in situ by using the preheating rod in cooperation with a defocused laser, the condition that the upper part of the welding seam is seriously burned but the bottom part is not penetrated due to the large thickness of the base material is improved, the melted alloy is extruded and scraped from the welding seam, and the joint performance unevenness caused by a small amount of evaporation of the liquid metal is improved.

Description

Technical Field

[0001] This application relates to the field of welding technology, and in particular to an apparatus and method for reducing element burn-off in laser welding of magnesium-lithium alloys. Background Technology

[0002] Magnesium-lithium alloys use magnesium as the base material and also contain lithium, both of which are typical lightweight metals. Compared to pure magnesium, magnesium-lithium alloys exhibit higher strength and better toughness due to lithium solid solution strengthening and the formation of the β phase. As an ideal material for lightweight, high-strength components, magnesium-lithium alloys are widely used in the manufacture of various critical aerospace components, such as seat frames, instrument panel parts, and control box housings. Therefore, achieving high-quality welding of magnesium-lithium alloys is crucial.

[0003] Studies have shown that the magnesium to lithium ratio in magnesium-lithium alloys significantly affects the microstructure and corresponding mechanical properties. For Mg-Li binary alloys, the lithium content is less than 5.7% when it is in the α phase, between 5.7% and 10.3% when it is in the α+β phase, and greater than 10.3% when it is in the β phase. Because both magnesium and lithium are highly volatile upon heating (lithium has a boiling point of only 1340℃, and magnesium has an even lower boiling point of only 1107℃), the evaporation and burning loss of magnesium and lithium in the liquid metal during magnesium-lithium alloy welding is significant, leading to changes in the magnesium to lithium ratio in the weld. Especially for α+β phase magnesium-lithium alloys, even a small amount of evaporation of the liquid metal can cause a significant change in the weld microstructure compared to the base metal, affecting the uniformity of the mechanical properties of the weld joint.

[0004] Currently, the main method used to address the problem of element evaporation and burn-off during the welding of magnesium-lithium alloys is to strictly control the welding heat input to avoid excessive evaporation of elements due to excessive heat input. However, for thick magnesium-lithium alloy plates, the welding process window is inherently narrow, and controlling the welding heat input to reduce evaporation can easily lead to incomplete penetration of the joint, making it difficult to form an effective connection. Summary of the Invention

[0005] To address the issue of element evaporation and burn-off affecting welding quality during magnesium-lithium alloy welding, this application provides an apparatus and method for reducing element burn-off in laser-welded magnesium-lithium alloy welds.

[0006] The device for reducing element burn-off in laser welding of magnesium-lithium alloys provided in this application adopts the following technical solution:

[0007] An apparatus for reducing element burn-off in laser welding of magnesium-lithium alloys, comprising:

[0008] The base is provided with a clamp for fixing two magnesium-lithium alloy base materials side by side, and the upper end face of the base is provided with a through groove parallel to the weld below the weld.

[0009] The guide rail is vertically mounted in the through groove;

[0010] A preheating rod is slidably mounted on the guide rail. The preheating rod includes a rod body and a preheating end fixed to one end of the rod body. The preheating end is located outside the through groove.

[0011] The first linear drive component is disposed in the through groove and is used to drive the guide rail to rise and fall, so that the upper surface of the rod abuts against or moves away from the lower surface of the connection between the two magnesium-lithium alloy base materials;

[0012] The extrusion mechanism is used to drive two pieces of magnesium-lithium alloy base material to be extruded horizontally toward the weld seam, so that the unsolidified liquid metal at the weld seam is squeezed out.

[0013] The upper scraper is slidably positioned above the weld seam to scrape off the liquid metal extruded from the upper surface of the weld seam;

[0014] The lower scraper is slidably mounted on the guide rail and slides synchronously with the preheating rod. It is used to scrape off the liquid metal extruded from the lower surface of the weld. The lower scraper is located at the end of the guide rail away from the preheating end, and the upper end of the lower scraper is higher than the upper surface of the rod.

[0015] Before welding, two magnesium-lithium alloy base materials are first fixed side by side on the base using a clamp. The first linear drive unit drives the guide rail to rise in the through groove, so that the upper surface of the rod abuts against the lower surface of the connection between the two magnesium-lithium alloy base materials. Then, a defocused laser is used to heat the preheating end, and the heat is conducted through the rod to the lower surface of the connection between the magnesium-lithium alloy base materials. After preheating, the first linear drive unit drives the guide rail to descend in the through groove, so that the rod separates from the lower surface of the magnesium-lithium alloy base materials. Then, the defocused laser is switched to a focused laser, and the magnesium-lithium alloy base materials are welded using a focused laser.

[0016] After welding is completed, the unsolidified liquid metal at the weld joint is extruded by an extrusion mechanism. The height of the guide rail is adjusted by the first linear drive component, so that the lower scraper abuts against the lower surface of the weld joint. The upper and lower scrapers move along the upper and lower surfaces of the weld joint respectively, scraping away the extruded liquid metal at the weld joint. Subsequently, the pressure of the extrusion mechanism is maintained, and a defocused laser is used to perform cyclic scanning along the weld joint.

[0017] By preheating the lower surface of the base material joint, the temperature difference between different areas in the thickness direction of the base material is reduced, which improves the situation where the upper part of the weld is severely burned but the bottom is still not fully penetrated due to the large thickness of the base material. It also helps to improve the problem of weld formation deterioration caused by excessive evaporation of molten pool metal.

[0018] On the other hand, the preheating step does not require the introduction of an additional heat source outside the welding equipment. In-situ preheating of the lower surface of the base material joint can be achieved using only the laser light source on the welding equipment, which helps to simplify the equipment and improve the convenience of operation. The rod only performs local preheating on the lower surface of the base material joint, without affecting the performance of other parts of the base material. After preheating, the rod separates from the base material, and the welding process is not affected by the preheated rod.

[0019] Because even a small amount of evaporation of liquid metal can cause changes in the magnesium-lithium ratio in the weld, affecting the uniformity of microstructure and mechanical properties, the molten magnesium-lithium alloy is extruded from the weld and promptly removed after welding. This improves the problem of uneven overall mechanical properties of the joint caused by changes in the microstructure of the weld compared to the base material after the molten metal solidifies. Simultaneously, under the action of the extrusion mechanism, after the molten metal is extruded, a bond forms between the unmelted areas of the two base materials, and an effective connection is formed under the solidification of a small amount of residual liquid metal.

[0020] Furthermore, under continuous pressure and post-weld heat treatment, diffusion occurs between the unmelted areas of the two base materials, further improving the joint quality. Thus, this application effectively mitigates the problems of weld formation deterioration and uneven joint mechanical properties caused by the violent evaporation of the molten metal in the weld pool, contributing to improved welding quality.

[0021] Furthermore, when the upper surface of the rod abuts against the lower surface of the connection between the two magnesium-lithium alloy base materials, the upper surface of the preheating end is flush with the upper surface of the magnesium-lithium alloy base material.

[0022] During the welding process, the distance between the laser source on the welding equipment and the base material is usually fixed, that is, the welding working distance is a constant value. The switching between defocusing and focusing is achieved by changing the focal length of the laser. During preheating, the upper surface of the preheating end is flush with the upper surface of the magnesium-lithium alloy base material, which is equivalent to the working distance between the preheating end and the base material being equal. The relative distance between the two and the laser focal length changes synchronously. After preheating, the rapid adjustment and switching between defocused and focused lasers can be achieved without adjusting the height of the laser source, which helps to improve work efficiency.

[0023] Furthermore, the preheating rod is made of copper.

[0024] Copper preheating rods have good thermal conductivity, which is conducive to efficient heat transfer.

[0025] Furthermore, the extrusion mechanism includes a second linear drive member disposed on both sides of the base, and an elongated pressure plate is fixedly connected to the output end of the second linear drive member, the pressure plate abutting against the side of the magnesium-lithium alloy base material.

[0026] The pressure of the second linear drive component is transmitted to the side of the magnesium-lithium alloy substrate through the long strip pressure plate, thereby achieving uniform and stable pressure on the side of the magnesium-lithium alloy substrate.

[0027] This application provides a method for reducing element burn-off in laser welding of magnesium-lithium alloys, employing an apparatus for reducing element burn-off in laser welding of magnesium-lithium alloys. The method includes the following steps:

[0028] Base material clamping: Fix two magnesium-lithium alloy base materials side by side on the base;

[0029] Preheating before welding: The first linear drive unit drives the guide rail to rise, so that the upper surface of the rod abuts against the lower surface of the connection between the two magnesium-lithium alloy base materials. The preheating end is heated by a defocused laser. Then the first linear drive unit drives the guide rail to fall, so that the rod separates from the magnesium-lithium alloy base material.

[0030] Laser welding: Two magnesium-lithium alloy base materials are welded using a focused laser;

[0031] Liquid metal extrusion and scraping: The unsolidified liquid metal at the weld is extruded by the extrusion mechanism; the height of the guide rail is adjusted by the first linear drive component so that the lower scraper abuts against the lower surface of the weld; the upper scraper and the lower scraper move along the upper and lower surfaces of the weld respectively to scrape off the extruded liquid metal at the weld.

[0032] Post-weld heat treatment: Maintain the pressure applied by the extrusion mechanism and use a defocused laser to perform cyclic scanning along the weld.

[0033] Furthermore, in the preheating step before welding, the power of the defocused laser is 200W to 400W, the flow rate of the protective gas is 15L / min to 25L / min, and the defocusing amount is 5mm to 10mm.

[0034] Furthermore, in the preheating step before welding, the preheating time is 60s to 100s, and the preheating temperature of the lower surface of the magnesium-lithium alloy base material connection is 200 to 300℃.

[0035] Furthermore, in the laser welding step, the focused laser power is 800W to 1200W, the welding speed is 5mm / s to 10mm / s, and the shielding gas flow rate is 15L / min to 25L / min.

[0036] Furthermore, in the liquid metal extrusion and scraping step, the extrusion mechanism applies a pressure of 50MPa to 100MPa to the magnesium-lithium alloy substrate, and the moving speed of the upper and lower scrapers is 3mm / s to 5mm / s.

[0037] Furthermore, in the post-weld heat treatment step, the defocusing laser power is 200W to 400W, the moving speed is 5mm / s to 10mm / s, the protective gas flow rate is 15L / min to 25L / min, the defocusing amount is 5mm to 10mm, and the number of cycles of heating is 5 to 10.

[0038] In summary, this application includes at least one of the following beneficial technical effects:

[0039] 1. By preheating the lower surface of the base metal joint, the temperature difference between different areas in the thickness direction of the base metal is reduced, which improves the situation where the upper part of the weld is severely burned but the bottom is still not penetrated due to the large thickness of the base metal. It also helps to improve the problem of weld formation deterioration caused by excessive evaporation of molten pool metal. The preheating rod consisting of a rod body and a preheating end is used. The preheating step does not require the introduction of an additional heat source outside the welding equipment. In-situ preheating of the lower surface of the base metal joint can be achieved using only the laser light source on the welding equipment.

[0040] 2. After welding, the molten magnesium-lithium alloy is extruded from the weld and removed in time, which improves the problem of uneven overall mechanical properties of the joint caused by the change in the microstructure of the weld after the solidification of the molten metal compared with the base material; at the same time, under the action of the extrusion mechanism, after the molten metal is extruded, the unmelted areas of the two base materials are bonded together, and an effective connection is formed under the solidification of a small amount of residual liquid metal.

[0041] 3. Under continuous pressure and post-weld heat treatment, diffusion occurs between the unmelted areas of the two base materials, further improving the connection quality. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application;

[0043] Figure 2 This is a partial schematic diagram in the embodiments of this application, mainly used to show the base, preheating rod and extrusion mechanism;

[0044] Figure 3 This is a partial schematic diagram used in the embodiments of this application to mainly show the guide rail, preheating rod and lower scraper;

[0045] Figure 4 This is a schematic diagram of the preheating of magnesium-lithium alloy before welding in the embodiments of this application;

[0046] Figure 5 This is a diagram showing the relative positions of the base material and the preheating rod during the preheating of the magnesium-lithium alloy before welding in an embodiment of this application.

[0047] Figure 6 This is a schematic diagram of laser welding of magnesium-lithium alloy in an embodiment of this application;

[0048] Figure 7 This is a diagram showing the relative positions of the base material and the preheating rod during laser welding of magnesium-lithium alloy in the embodiments of this application;

[0049] Figure 8 This is a schematic diagram of the post-weld extrusion mechanism in operation in an embodiment of this application;

[0050] Figure 9 This is a schematic diagram used in the embodiments of this application to mainly illustrate the working state of the scraper;

[0051] Figure 10 This is a schematic diagram of post-weld heat treatment in an embodiment of this application;

[0052] Figure 11 This is a diagram showing the relative positions of the base material and the pressure plate during post-weld heat treatment in an embodiment of this application.

[0053] Figure 12 This is a diagram showing the relative positions of the base material and the preheating rod during post-weld heat treatment in an embodiment of this application.

[0054] Reference numerals in the attached drawings: 1. Magnesium-lithium alloy base material one; 2. Magnesium-lithium alloy base material two; 3. Base; 301. Preheating rod; 301-1. Rod body; 301-2. Preheating end; 302. Lower scraper; 303. Guide rail; 304. Second linear drive component; 304-1. Second hydraulic rod; 304-2. Pressure plate; 305. First linear drive component; 305-1. First hydraulic rod; 4. Defocused laser; 5. Focused laser; 6. Upper scraper; 7. Extruded liquid metal; 8. Robotic arm. Detailed Implementation

[0055] The following is in conjunction with the appendix Figure 1-12 This application will be described in further detail.

[0056] Example 1

[0057] This application discloses an apparatus for reducing elemental burn-off in laser welding of magnesium-lithium alloys. (Refer to...) Figure 1 and Figure 2 The device for reducing element burn-off in laser welding of magnesium-lithium alloy includes a base 3 and a clamp set on the base 3. The clamp is used to fix two magnesium-lithium alloy base materials side by side. A through groove parallel to the weld is opened on the upper end surface of the base 3 below the weld.

[0058] Reference Figure 2 and Figure 3 The through groove is provided with a guide rail 303 and a first linear drive 305 for driving the guide rail 303 to rise and fall. The first linear drive 305 is a hydraulic device, including a plurality of first hydraulic rods 305-1 spaced apart in the through groove, and the output end of the first hydraulic rods 305-1 is connected to the lower end face of the guide rail 303.

[0059] Reference Figure 2 and Figure 3 A copper preheating rod 301 is slidably mounted on the guide rail 303. The preheating rod 301 includes a rod body 301-1 and a preheating end 301-2 fixed to one end of the rod body 301-1. The preheating end 301-2 is located outside the through groove. The length of the rod body 301-1 is greater than the length of the weld. The rod body 301-1 is a square rod, and the preheating end 301-2 is square-shaped.

[0060] Reference Figure 4 and Figure 6 The laser source on the welding equipment is slidably positioned above the magnesium-lithium alloy base material along the length of the weld seam to provide focused laser 5 and defocused laser 4; wherein focused laser 5 is used for welding, and defocused laser 4 is used to heat the upper surface of the preheated end 301-2 and to perform post-weld heat treatment on the base material.

[0061] Before welding, magnesium-lithium alloy base material 1 and magnesium-lithium alloy base material 2 are first fixed side by side on the base 3 using a clamp. The guide rail 303 is then driven to rise in the through groove by the first hydraulic rod 305-1, causing the upper surface of the rod 301-1 to abut against the lower surface of the connection point between the two magnesium-lithium alloy base materials. Figure 4 and Figure 5 As shown. Then, a defocused laser 4 is used to heat the preheated end 301-2, and the heat is conducted through the rod 301-1 to the lower surface of the magnesium-lithium alloy base material at the joint. After preheating, the first hydraulic rod 305-1 drives the guide rail 303 to descend in the through slot, separating the rod 301-1 from the lower surface of the magnesium-lithium alloy base material; then, the defocused laser 4 is switched to a focused laser 5, and the focused laser 5 is used to weld the magnesium-lithium alloy base material, as shown. Figure 6 and Figure 7 As shown.

[0062] By preheating the lower surface of the base material joint, the temperature difference between different areas in the thickness direction of the base material is reduced, which improves the situation where the upper part of the weld is severely burned but the bottom is still not fully penetrated due to the large thickness of the base material. It also helps to improve the problem of weld formation deterioration caused by excessive evaporation of molten pool metal.

[0063] On the other hand, the preheating step does not require the introduction of an additional heat source outside the welding equipment. The laser light source on the welding equipment can be used to achieve in-situ preheating of the lower surface of the base material joint, which is conducive to simplifying the equipment and improving the convenience of operation. The rod 301-1 only performs local preheating on the lower surface of the base material joint, without affecting the performance of other parts of the base material. After preheating, the rod 301-1 separates from the base material, and the welding process is not affected by the preheating rod 301.

[0064] Reference Figure 5When the upper surface of the rod 301-1 abuts against the lower surface of the connection between the two magnesium-lithium alloy base materials, the upper surface of the preheating end 301-2 is flush with the upper surface of the magnesium-lithium alloy base material.

[0065] During the welding process, the distance between the laser source on the welding equipment and the base material is usually fixed, that is, the welding working distance is a constant value. The switching between defocusing and focusing is achieved by changing the focal length of the laser. During preheating, the upper surface of the preheating end 301-2 is flush with the upper surface of the magnesium-lithium alloy base material, which is equivalent to the working distance between the preheating end 301-2 and the base material being equal. The relative distance between the two and the laser focal length changes synchronously. The rapid adjustment and switching between defocusing laser 4 and focusing laser 5 can be achieved without adjusting the height of the laser source, which helps to improve work efficiency.

[0066] Reference Figure 1 and Figure 2 The base 3 is provided with extrusion mechanisms on both sides of the base material. Specifically, the extrusion mechanism includes a second linear drive 304 provided on both sides of the base 3. The second linear drive 304 includes a plurality of second hydraulic rods 304-1 arranged at intervals along the side of the base material. The output end of the second hydraulic rods 304-1 is fixedly connected to a long strip pressure plate 304-2, and the pressure plate 304-2 abuts against the side of the magnesium-lithium alloy base material.

[0067] Reference Figure 8 An upper scraper 6 is slidably disposed above the weld, and the upper scraper 6 is driven by a robotic arm 8 to scrape off the liquid metal 7 squeezed out from the upper surface of the weld.

[0068] Reference Figure 5 and Figure 7 A lower scraper 302 is also slidably mounted on the guide rail 303 to scrape off the liquid metal extruded from the lower surface of the weld. The lower scraper 302 is located at the end of the guide rail 303 away from the preheating end 301-2, and the upper end of the lower scraper 302 is higher than the upper surface of the rod 301-1. Both the lower scraper 302 and the preheating rod 301 are driven by a motor and slide synchronously on the guide rail 303. Both the upper scraper 6 and the lower scraper 302 are made of 316L stainless steel.

[0069] After welding is completed, the pressure plate 304-2 is driven by the second hydraulic rods 304-1 on both sides of the base material to apply pressure to the two base materials towards the weld, squeezing out the unsolidified liquid metal at the weld. The height of the guide rail 303 in the through groove is adjusted by the first hydraulic rod 305-1, so that the lower scraper 302 abuts against the lower surface of the weld. Figure 9 As shown. Then, the upper scraper 6 is driven by the robotic arm 8, and the lower scraper 302 is driven by the motor to slide along the guide rail 303. The upper scraper 6 and the lower scraper 302 move along the upper and lower surfaces of the weld, respectively, to scrape off the liquid metal 7 that has been squeezed out at the weld.

[0070] Because even a small amount of evaporation of liquid metal can cause changes in the magnesium-lithium ratio in the weld, affecting the uniformity of microstructure and mechanical properties, the molten magnesium-lithium alloy is extruded from the weld and promptly removed after welding. This improves the problem of uneven overall mechanical properties of the joint caused by changes in the microstructure of the weld compared to the base material after the molten metal solidifies. Simultaneously, under the action of the extrusion mechanism, after the molten metal is extruded, a bond forms between the unmelted areas of the two base materials, and an effective connection is formed under the solidification of a small amount of residual liquid metal.

[0071] After scraping away the molten metal squeezed out of the weld, maintain the pressure applied by the extrusion mechanism, switch the focused laser 5 to the defocused laser 4, and use the defocused laser 4 to perform cyclic scanning along the weld. Figure 10 , Figure 11 and Figure 12 As shown, under continuous pressure and post-weld heat treatment, diffusion occurs between the unmelted areas of the two base materials, further improving the joint quality. Thus, this application effectively improves the problems of weld formation deterioration and uneven joint mechanical properties caused by the violent evaporation of the molten metal in the weld pool, which is beneficial to improving welding quality.

[0072] Example 2

[0073] This application discloses a method for reducing element burn-off in laser welding of magnesium-lithium alloys, using the apparatus for reducing element burn-off in laser welding of magnesium-lithium alloys disclosed in Example 1. The method includes the following steps:

[0074] Step 1: Pre-treatment of base material before welding: The mating surfaces and surfaces of the 8mm thick LAZ933 magnesium-lithium alloy base material to be welded are mechanically ground in sequence using sandpaper of 80#, 200#, 400#, 600#, 800# and 1000#. Then, it is cleaned in anhydrous ethanol for 7 minutes and vacuum dried for 30 minutes after cleaning.

[0075] The chemical composition of LAZ933 base material includes Li: 9wt%, Al: 3wt%, Zn: 3wt%, and Mg: balance.

[0076] Step 2, Clamping of the base material: Fix the two magnesium-lithium alloy base materials side by side on the base 3 using clamps;

[0077] Step 3, Preheating before welding: The first hydraulic rod 305-1 drives the guide rail 303 to rise, so that the upper surface of the rod 301-1 abuts against the lower surface of the connection between the two magnesium-lithium alloy base materials. The preheating end 301-2 is heated by the defocused laser 4 with a power of 400W, a protective gas flow rate of 20L / min, a defocusing amount of 8mm, and a preheating time of 80s, so that the preheating temperature of the lower surface of the connection between the magnesium-lithium alloy base materials reaches 200℃. Then, the first hydraulic rod 305-1 drives the guide rail 303 to fall, so that the rod 301-1 separates from the magnesium-lithium alloy base materials.

[0078] Step 4, Laser Welding: Switch the defocused laser 4 to the focused laser 5, and use the focused laser 5 to weld the two magnesium-lithium alloy base materials to ensure complete melting of the base materials; wherein, the power of the focused laser 5 is 1000W, the welding speed is 5mm / s, and the shielding gas flow rate is 20L / min.

[0079] Step 5, Liquid Metal Extrusion and Scraping: The unsolidified liquid metal at the weld is extruded by the second hydraulic rod 304-1, and the pressure plate 304-2 applies a pressure of 80MPa; the height of the guide rail 303 is adjusted by the first hydraulic rod 305-1 so that the lower scraper 302 abuts against the lower surface of the weld; the upper scraper 6 and the lower scraper 302 move along the upper and lower surfaces of the weld respectively, with a moving speed of 5mm / s, to scrape away the extruded liquid metal at the weld.

[0080] Step 6, Post-weld heat treatment: Maintain the pressure state of the extrusion mechanism, switch the focused laser 5 to the defocused laser 4, and use the defocused laser 4 to perform cyclic scanning along the weld; wherein, the power of the defocused laser 4 is 400W, the moving speed is 5mm / s, the protective gas flow rate is 20L / min, the defocusing amount is 8mm, and the number of cyclic scanning is 10.

[0081] Step 7: After welding is complete, remove the welded part from the fixture.

[0082] The comparative example uses conventional welding methods: the pre-welding treatment and clamping steps of the base material are the same as steps one and two in Example 2, no preheating is performed before welding, the laser welding steps are the same as step four in Example 2, and the molten metal is not squeezed or scraped off after welding, nor is post-weld heat treatment performed.

[0083] The welded joints obtained in Example 2 and the comparative example were subjected to visual observation, tensile strength and elongation after fracture tests. The test results are as follows: The welded joint obtained in Example 2 had no V-shaped groove on the upper surface. The tensile strength of the welded joint reached 183 MPa and the elongation after fracture was 23%, which reached 91% and 88% of the base material, respectively, which were significantly higher than 105 MPa and 13% of conventional welding.

[0084] The test results show that the method provided in this application reduces the evaporation and burning loss of elements in the weld seam of magnesium-lithium alloy laser welding, and effectively improves the forming quality and the uniformity of the mechanical properties of the joint.

[0085] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A device for reducing elemental burn-off in laser welding of magnesium-lithium alloys, characterized in that: include: The base is provided with a clamp for fixing two magnesium-lithium alloy base materials side by side, and the upper end surface of the base is provided with a through groove parallel to the weld below the weld. The guide rail is vertically mounted in the through groove; A preheating rod is slidably mounted on the guide rail. The preheating rod includes a rod body and a preheating end fixed to one end of the rod body. The preheating end is located outside the through groove. The first linear drive component is disposed in the through groove and is used to drive the guide rail to rise and fall, so that the upper surface of the rod abuts against or moves away from the lower surface of the connection between the two magnesium-lithium alloy base materials; The extrusion mechanism is used to drive two pieces of magnesium-lithium alloy base material to be extruded horizontally toward the weld seam, so that the unsolidified liquid metal at the weld seam is squeezed out. The upper scraper is slidably positioned above the weld seam to scrape off the liquid metal extruded from the upper surface of the weld seam; The lower scraper is slidably mounted on the guide rail and slides synchronously with the preheating rod. It is used to scrape off the liquid metal extruded from the lower surface of the weld. The lower scraper is located at the end of the guide rail away from the preheating end, and the upper end of the lower scraper is higher than the upper surface of the rod.

2. The device for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 1, characterized in that: When the upper surface of the rod abuts against the lower surface of the connection between the two magnesium-lithium alloy base materials, the upper surface of the preheating end is flush with the upper surface of the magnesium-lithium alloy base material.

3. The device for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 1, characterized in that: The preheating rod is made of copper.

4. The device for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 1, characterized in that: The extrusion mechanism includes a second linear drive unit disposed on both sides of the base. The output end of the second linear drive unit is fixedly connected to a long strip-shaped pressure plate, which abuts against the side of the magnesium-lithium alloy base material.

5. A method for reducing element burn-off in laser welding of magnesium-lithium alloys, characterized in that: The apparatus for reducing element burn-off in laser welding of magnesium-lithium alloys according to any one of claims 1-4 includes the following steps: Base material clamping: Fix two magnesium-lithium alloy base materials side by side on the base; Preheating before welding: The first linear drive unit drives the guide rail to rise, so that the upper surface of the rod abuts against the lower surface of the connection between the two magnesium-lithium alloy base materials. The preheating end is heated by a defocused laser. Then the first linear drive unit drives the guide rail to fall, so that the rod separates from the magnesium-lithium alloy base material. Laser welding: Two magnesium-lithium alloy base materials are welded using a focused laser; Liquid metal extrusion and scraping: The unsolidified liquid metal at the weld is extruded by the extrusion mechanism; the height of the guide rail is adjusted by the first linear drive component so that the lower scraper abuts against the lower surface of the weld; the upper scraper and the lower scraper move along the upper and lower surfaces of the weld respectively to scrape off the extruded liquid metal at the weld. Post-weld heat treatment: Maintain the pressure applied by the extrusion mechanism and use a defocused laser to perform cyclic scanning along the weld.

6. The method for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 5, characterized in that: In the preheating step before welding, the power of the defocused laser is 200W to 400W, the flow rate of the protective gas is 15L / min to 25L / min, and the defocusing amount is 5mm to 10mm.

7. The method for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 6, characterized in that: In the preheating step before welding, the preheating time is 60s to 100s, and the preheating temperature of the lower surface of the magnesium-lithium alloy base material connection is 200 to 300℃.

8. The method for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 5, characterized in that: In the laser welding step, the focused laser power is 800W to 1200W, the welding speed is 5mm / s to 10mm / s, and the shielding gas flow rate is 15L / min to 25L / min.

9. A method for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 5, characterized in that: In the liquid metal extrusion and scraping step, the extrusion mechanism applies a pressure of 50MPa to 100MPa to the magnesium-lithium alloy base material, and the moving speed of the upper and lower scrapers is 3mm / s to 5mm / s.

10. A method for reducing element burn-off in laser welding of magnesium-lithium alloys according to claim 5, characterized in that: In the post-weld heat treatment step, the defocused laser power is 200W to 400W, the moving speed is 5mm / s to 10mm / s, the protective gas flow rate is 15L / min to 25L / min, the defocusing amount is 5mm to 10mm, and the number of cycles of heating is 5 to 10.

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