Magnesium alloy welding method

Abstract

The magnesium alloy welding method comprises the steps that a Cu-Zn alloy serves as a middle layer, and the magnesium alloy is prepared through the TLP technology; the TLP process parameters are as follows: under inert gas, the magnesium alloy to-be-welded part is heated to 440-450 DEG C, then the temperature is reduced to 420-430 DEG C, heat preservation is carried out for 10-20 min, and the magnesium alloy to-be-welded part is obtained after cooling. According to the improved TLP technology, the copper-zinc alloy serves as the middle layer, high-quality welding of the magnesium alloy can be achieved under the low temperature, short time and small pressure, and the problems that a large amount of water overflows from the surface of an existing U-TLP magnesium alloy welding joint, and industrial popularization is difficult are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and in particular relates to a method for welding magnesium alloys. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, have advantages such as high specific strength, high specific stiffness, excellent shock absorption performance, excellent electromagnetic shielding, and good heat dissipation. They are widely used in aerospace, automotive industry, medical devices, 3C electronics and other fields.

[0003] Currently, the main welding methods for joining magnesium alloys are fusion welding and solid-state welding. Solid-state welding technology is difficult to promote on a large scale in industry due to its long welding time and high requirements for surface finish. Fusion welding technology is relatively mature and can achieve high strength, but it damages the structural integrity of the base material, making it unsuitable for precision connections in complex structures. Furthermore, the residual thermal stress generated during fusion welding also affects the joint's performance. U-TLP welding technology relies on ultrasonic vibration to extrude the brittle phase to obtain a high-strength joint, but due to the size limitations of the ultrasonic head, it is difficult to apply to large-sized workpieces in actual production. Additionally, the extrusion of the liquid phase causes significant overflow and erosion on the base material surface, damaging its surface structure and requiring post-weld treatment. Moreover, the holding time in existing TLP welding processes is mostly between 30 and 60 minutes, which can increase production costs if the time is too long.

[0004] For interlayers, existing interlayers for joining magnesium alloys are mostly single-metal interlayers or composite interlayers. Single-metal interlayers, such as pure copper or nickel, require high welding temperatures when welded to magnesium alloys, which can lead to severe erosion of the joint. Furthermore, high-temperature welding may cause coarse grains in the base material, further affecting its properties and hindering high-quality magnesium alloy bonding. Composite interlayers employ multi-layer structures, which are cumbersome in practical production applications, significantly increasing the welding difficulty. Therefore, providing a welding process suitable for welding large-size magnesium alloys and explaining the application of welding interlayers for magnesium alloys is of great significance. Summary of the Invention

[0005] Based on the above-mentioned technical problems, the present invention provides an improved TLP process, which uses a copper-zinc alloy as an intermediate layer, and can achieve high-quality welding of magnesium alloys at lower temperatures, shorter times and lower pressures. This effectively solves the problems of excessive overflow on the joint surface and difficulty in industrial application of existing U-TLP magnesium alloy welding.

[0006] The specific solution of this invention is as follows:

[0007] This invention provides a magnesium alloy welding method, comprising: using a Cu-Zn alloy as an intermediate layer and preparing it using a TLP process; the TLP process parameters are: heating the magnesium alloy workpiece to be welded to 440-450°C under an inert gas, then lowering the temperature to 420-430°C, holding it at that temperature for 10-20 minutes, and then cooling it to obtain the final product.

[0008] Preferably, the TLP process parameters are: heating the magnesium alloy workpiece to be welded to 440-450°C, then lowering the temperature to 430°C and holding it for 15 minutes.

[0009] Preferably, the magnesium alloy workpiece to be welded is assembled by placing a Cu-Zn alloy as an intermediate layer between magnesium alloy base materials.

[0010] Preferably, the mass fraction of Zn in the Cu-Zn alloy is 35-40%; more preferably, it is 38%.

[0011] Preferably, the thickness of the intermediate layer is 10–30 μm.

[0012] Preferably, the magnesium alloy comprises, by mass percentage: Al 2.78–2.88%, Zn 0.8–0.81%, Mn 0–0.3%, Si 0–0.24%, Cu 0–0.0034%, Ni 0–0.001%, with the balance being magnesium.

[0013] Preferably, in the TLP process, the applied pressure is 0.01-0.1 MPa.

[0014] Preferably, the inert gas is argon; the flow rate of the inert gas is 3.5 to 4 L / min.

[0015] The beneficial effects of this invention are:

[0016] This invention employs a modified TLP (Temperature-Lifted Lamination) process, which involves first melting the alloy interlayer at high temperature, followed by welding the magnesium alloy using a cooling and holding method. This process, using a Cu-Zn alloy as the interlayer, enables rapid solidification of the weld. The entire process is simple, requires no complex equipment, and overcomes the size limitations of the U-TLP process. It achieves high-quality welding of magnesium alloys at lower temperatures, shorter times, and lower pressures, showing promise for industrial applications. Attached Figure Description

[0017] Figure 1 The microstructure morphology of the joint obtained in Example 2;

[0018] Figure 2 The microstructure morphology of the joint obtained in Comparative Example 3 is shown.

[0019] Figure 3Schematic diagram of pressure shearing of magnesium alloy welded joint;

[0020] Figure 4 The images show the macroscopic morphology of the magnesium alloys obtained in Example 2 and Comparative Examples 1-3, where (a) is Example 2 and (b) to (d) correspond to Comparative Examples 1-3, respectively. Detailed Implementation

[0021] This invention provides a magnesium alloy welding method, comprising: using a Cu-Zn alloy as an intermediate layer and preparing it using a TLP process; the TLP process parameters are: heating the magnesium alloy workpiece to be welded to 440-450°C under an inert gas, then lowering the temperature to 420-430°C, holding it at that temperature for 10-20 minutes, and then cooling it to obtain the final product.

[0022] Preferably, the mass fraction of Zn in the Cu-Zn alloy is 35-40%; more preferably, it is 38%.

[0023] This invention employs a modified TLP process, specifically: first, the alloy interlayer is melted at a high temperature, and then, through a cooling and holding method, the interlayer diffuses and solidifies at a lower temperature. Compared to the U-TLP process, this avoids the damage to the surface structure of the base material caused by excessive overflow and erosion, as well as the reduction in workpiece size, while also ensuring the strength of the magnesium alloy welded joint.

[0024] The process described in this invention is suitable for processing large-sized workpieces, overcoming the limitations of ultrasonic head size. The entire process eliminates the need for relatively complex ultrasonic, pulse pressure, and electric field conditions, and places lower demands on welding equipment; only a shielding gas needs to be introduced during welding. Compared to similar TLP welding technologies for magnesium alloys, this invention is relatively simple to operate, produces stable results, and is suitable for industrial applications.

[0025] To facilitate this process, this invention employs a Cu-Zn alloy as the interlayer. By introducing a high copper content, rapid solidification of the weld is achieved, thereby reducing liquid phase overflow. Compared to the large, continuous weld structure of a pure zinc interlayer, the addition of copper transforms the weld structure from a large, continuous compound into a small, dispersed compound. This results in more magnesium-based solid solution within the weld, thus improving its strength. Simultaneously, a magnesium alloy joint with less overflow is obtained, effectively reducing the number of post-weld processing steps.

[0026] The process described in this invention is particularly suitable for magnesium alloys with the following composition: Al 2.78–2.88%, Zn 0.8–0.81%, Mn 0–0.3%, Si 0–0.24%, Cu 0–0.0034%, Ni 0–0.001%, with the balance being magnesium. Because this magnesium alloy composition has an Al content of 2.78–2.88%, it can undergo a ternary eutectic reaction with Mg and Cu under these conditions, further reducing the welding temperature to 440°C. Other magnesium alloys without Al require welding temperatures to be increased to 450°C or higher, increasing the risk of overflow.

[0027] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0028] Example 1

[0029] A method for welding magnesium alloys includes the following steps:

[0030] (1) Preprocessing

[0031] The magnesium alloy base material was processed into two test plates of different sizes: 30mm×20mm×3mm and 18mm×8mm×3mm. The intermediate layer foil was cut into a rectangle of 18mm×8mm.

[0032] Before welding, the base material was polished with 200#, 400#, 600#, 800# and 1000# sandpaper respectively. Then, the magnesium alloy base material was ultrasonically cleaned in ethanol solution for 10 minutes, and the intermediate layer was ultrasonically cleaned in ethanol for 1 minute.

[0033] The magnesium alloy composition, by mass percentage, includes: Al 2.78–2.88%, Zn 0.8–0.81%, Mn 0–0.3%, Si 0–0.24%, Cu 0–0.0034%, Ni 0–0.001%, with the balance being magnesium; the intermediate layer is a 20 μm thick H62 grade Cu-(38 wt.%) Zn alloy.

[0034] (2) TLP welding

[0035] The intermediate layer foil was placed between two magnesium alloy base materials, and a pressure of 0.02 MPa was applied to it. The workpiece was heated to 450°C by high-frequency induction heating, then cooled to 430°C and held at that temperature for 10 minutes. It was then allowed to cool naturally to room temperature. Ar gas (99.99% by mass) was used for protection throughout the entire heating, holding, and cooling process (flow rate 3.5–4 L / min).

[0036] Example 2

[0037] A magnesium alloy welding method differs from Example 1 only in that the holding time during TLP welding is adjusted to 15 minutes; all other processes and parameters are the same as in Example 1. The microstructure of the welded joint obtained in this example is as follows: Figure 1 As shown.

[0038] Example 3

[0039] A magnesium alloy welding method differs from Example 1 only in that the holding time during TLP welding is adjusted to 20 minutes, while other processes and parameters are the same as in Example 1.

[0040] Example 4

[0041] A magnesium alloy welding method differs from Example 2 only in that, during TLP welding, the workpiece to be welded is first heated to 440°C, and then cooled to 430°C and held for 15 minutes. All other processes and parameters are the same as in Example 2.

[0042] Example 5

[0043] A magnesium alloy welding method differs from Example 2 only in that, during TLP welding, the workpiece to be welded is first heated to 450°C, and then cooled to 420°C and held for 15 minutes. All other processes and parameters are the same as in Example 2.

[0044] Comparative Example 1

[0045] A magnesium alloy welding method, which differs from Example 2 only in the TLP process;

[0046] The TLP process in this comparative example is as follows: An interlayer foil is placed between two magnesium alloy base materials, and a pressure of 0.02 MPa is applied. The workpiece is then heated to 450°C using high-frequency induction heating and held at this temperature for 15 minutes; followed by natural cooling to room temperature. Ar gas (99.99% by mass) is used for protection throughout the entire heating, holding, and cooling process (flow rate 3.5–4 L / min); the interlayer is the same as in Example 2.

[0047] Comparative Example 2

[0048] A method for welding magnesium alloys includes the following steps:

[0049] (1) Preprocessing

[0050] The only difference from Example 2 is that the intermediate layer is replaced with a Zn foil with a thickness of 20 μm;

[0051] (2) TLP welding

[0052] The intermediate layer foil was placed between two magnesium alloy base materials, and a pressure of 0.02 MPa was applied to it. The workpiece was heated to 450°C by high-frequency induction heating, held at that temperature for 15 minutes, and then allowed to cool naturally to room temperature. Ar gas (99.99% by mass) was used for protection throughout the heating, holding, and cooling process (flow rate 3.5–4 L / min).

[0053] Comparative Example 3

[0054] A method for welding magnesium alloys includes the following steps:

[0055] (1) Preprocessing

[0056] The only difference from Example 2 is that the intermediate layer is replaced with a Zn foil with a thickness of 20 μm;

[0057] (2) TLP welding

[0058] The intermediate layer foil was placed between two magnesium alloy base materials, and a pressure of 0.02 MPa was applied. The workpiece was heated to 450°C using high-frequency induction heating, then cooled to 430°C and held at that temperature for 15 minutes, followed by natural cooling to room temperature. Ar gas (99.99% by mass) was used for protection throughout the entire heating, holding, and cooling process (flow rate 3.5–4 L / min).

[0059] The microstructure of the welded joint obtained in this comparative example is as follows: Figure 2 As shown.

[0060] Shear specimens of magnesium alloy welded joints obtained in the above embodiments and comparative examples are as follows: Figure 3 As shown in Table 1, compression and shear tests were conducted using an LD24204 electronic universal testing machine.

[0061] Table 1 shows the compressive shear strength of the welded joints obtained in the examples and comparative examples.

[0062]

[0063]

[0064] The macroscopic morphology of the magnesium alloys obtained in Example 2 and Comparative Examples 1-3 is as follows: Figure 4 As shown.

[0065] A comparison of the above data and the attached chart shows that:

[0066] (1) In Examples 1-3, a copper-zinc interlayer and a cooling and heat preservation process were used. As the heat preservation time increased, the weld strength showed a trend of first increasing and then decreasing. When the heat preservation time was increased from 10 min to 15 min, the weld fusion was more complete and the weld strength was improved. When the heat preservation time was increased to 20 min, more liquid phase flowed out of the weld, and the weld was prone to defects such as pores and cracks, resulting in a decrease in strength.

[0067] Further integration Figure 4 As can be seen, under the process conditions of Example 2, there was relatively little overflow and relatively little damage to the base material, thus protecting the structural integrity of the base material.

[0068] (2) As can be seen from the microstructure morphology diagrams and shear data of Example 2 and Comparative Example 3, the addition of copper to zinc transformed the weld structure from large continuous compounds to small dispersed compounds, and more magnesium-based solid solutions appeared in the weld. The reduction of compounds improved the weld strength.

[0069] (3) The comparison of the macroscopic morphology and shear strength of Comparative Example 1 and Comparative Example 2 shows that without the use of cooling and heat preservation process, the liquid phase after the copper-zinc and pure zinc intermediate layer melts is in an active state for a long time, which is easy to overflow and cause corrosion to the base material. Furthermore, due to the outflow of the liquid phase of the intermediate layer, pores are easy to appear in the weld, resulting in a decrease in the strength of the weld.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for welding magnesium alloys, characterized in that, include: It was prepared using a Cu-Zn alloy as the intermediate layer and the TLP process; The TLP process parameters are as follows: under inert gas, the magnesium alloy workpiece to be welded is heated to 440-450℃, then the temperature is lowered to 420-430℃, held for 10-20 minutes, and then cooled to obtain the final product.

2. The magnesium alloy welding method according to claim 1, characterized in that, The TLP process parameters are as follows: heat the magnesium alloy workpiece to be welded to 440-450℃, then lower the temperature to 430℃ and hold for 15 minutes.

3. The magnesium alloy welding method according to claim 1 or 2, characterized in that, The magnesium alloy workpiece to be welded is assembled by placing a Cu-Zn alloy as an intermediate layer between magnesium alloy base materials.

4. The magnesium alloy welding method according to claim 1 or 2, characterized in that, In Cu-Zn alloys, the mass fraction of Zn is 35-40%.

5. The magnesium alloy welding method according to claim 1 or 2, characterized in that, In the Cu-Zn alloy, the mass fraction of Zn is 38%.

6. The magnesium alloy welding method according to claim 1 or 2, characterized in that, The thickness of the intermediate layer is 10–30 μm.

7. The magnesium alloy welding method according to claim 1 or 2, characterized in that, The composition of magnesium alloy by mass percentage includes: Al 2.78-2.88%, Zn 0.8-0.81%, Mn 0-0.3%, Si 0-0.24%, Cu 0-0.0034%, Ni 0-0.001%, with the balance being magnesium.

8. The magnesium alloy welding method according to claim 1 or 2, characterized in that, In the TLP process, the applied pressure is 0.01-0.1 MPa.

9. The magnesium alloy welding method according to claim 1 or 2, characterized in that, The inert gas is argon; the flow rate of the inert gas is 3.5–4 L / min.

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