A method for improving magnesium alloy welding structure and performance

Abstract

The present invention provides a method for improving the welding structure and performance of magnesium alloys, and belongs to the field of metal material processing. In the prior art, it is very easy to form a strong and regularly distributed texture in the welding area of ​​magnesium alloys, and the joint is prone to strain localization during the loading and deformation process, resulting in a significant decrease in the mechanical properties of the joint. In view of the shortcomings in the prior art, the present invention provides a method for improving the welding structure and performance of magnesium alloys. In the present invention, a small deformation hot rolling process is first used to reduce defects such as weld metal collapse, pores and looseness in the welding area and regulate the regularly distributed texture of the welding area, but the deformed weld structure is easy to separate from the matrix during use, resulting in a decrease in welding performance. Therefore, after hot rolling deformation, the present invention uses ultrasonic assisted laser remelting technology to significantly fuse the organization of the welding area and the matrix area, greatly improve the bonding strength of the welding area and the matrix, and because the ultrasonic assisted forging effect can refine the grain structure of the remelting area, the surface shot peening is finally used to mainly improve the degree of finishing of the welding area and the matrix area and reduce the crack source. Therefore, the welding structure and performance of the magnesium alloy prepared by the present invention are significantly improved.

Description

Technical Field

[0001] The invention belongs to the field of metal material processing and relates to a method for improving the welding structure and performance of a magnesium alloy. Background Art

[0002] Magnesium alloy has the advantages of light weight, high specific strength and specific stiffness, excellent shock absorption, good electromagnetic shielding and thermal conductivity, and easy recycling. It has broad application prospects in the fields of automobile manufacturing, aerospace, electronics and electrical appliances, transportation, national defense, etc. The performance of magnesium alloy has significant characteristics compared with other materials, and its weldability is relatively special. Due to the low density, low melting point, high thermal conductivity and electrical conductivity, large thermal expansion coefficient, strong chemical activity, easy oxidation and high melting point of oxides of magnesium alloy, magnesium alloy is easy to produce weld metal collapse during welding, affecting the quality of weld formation. It is very easy to form a strong and regularly distributed texture in the micro-area of ​​the joint weld. Under the influence of this texture distribution, the joint is prone to strain localization during loading and deformation, resulting in a significant decrease in the mechanical properties of the joint. Therefore, exploring a method that can improve the welding structure and performance of magnesium alloys has important research significance and application value. Summary of the invention

[0003] In view of the shortcomings in the prior art, the present invention provides a method for improving the welding structure and performance of magnesium alloys. In the present invention, a small deformation hot rolling process is first used to reduce defects such as weld metal collapse, pores and looseness in the welding area and regulate the regularly distributed texture of the welding area. However, the deformed weld structure is easily separated from the matrix during use, resulting in a decrease in welding performance. Therefore, after hot rolling deformation, the present invention uses ultrasonic assisted laser remelting technology to significantly fuse the structures of the welding area and the matrix area, greatly improving the bonding strength of the welding area and the matrix, and because the ultrasonic assisted forging effect can refine the grain structure of the remelting area, the surface shot peening treatment is finally used mainly to improve the smoothness of the welding area and the matrix area and reduce the crack source. Therefore, the welding structure and performance of the magnesium alloy prepared by the present invention are significantly improved.

[0004] The present invention provides a method for improving the welding structure and performance of a magnesium alloy. The prepared magnesium alloy welding zone has a uniform and dense structure, a weld joint tensile strength of 250-290 MPa, an elongation of 7.1%-9.2%, and the performance of the magnesium alloy welding zone is significantly improved.

[0005] Furthermore, the magnesium alloy material is AZ91.

[0006] The present invention provides a method for improving the welding structure and performance of magnesium alloy, which specifically comprises the following steps:

[0007] (1) The magnesium alloy welding sheet is polished flat, then ultrasonically cleaned in alcohol, and dried with compressed nitrogen;

[0008] (2) Fixing the cleaned welded sheet on the working platform of the rolling mill, followed by small deformation hot rolling, and then removing the oxide layer;

[0009] (3) performing ultrasonic-assisted laser remelting on the surface of the magnesium alloy welding sheet workpiece obtained in step (2) under an argon protective atmosphere;

[0010] (4) Using shot peening equipment, the surface of the workpiece of the magnesium alloy welding sheet obtained in step (3) is surface strengthened.

[0011] Furthermore, in step (2), the hot rolling temperature is 350-460° C., and the rolling reduction is 10-20%.

[0012] Furthermore, in step (2), after hot rolling, the steel is cooled at a cooling rate of 30 to 40°C / s, cooled to 150 to 200°C, and then placed in a furnace for heat preservation, and after heat preservation for 40 to 60 minutes, cooled to room temperature in the furnace.

[0013] Furthermore, in step (3), the argon gas flow rate is 15 L / min, the laser power is 800-2000 W, the spot diameter is 2-6 mm, the scanning speed is 5-10 mm / s, and the overlap rate is 50%.

[0014] Furthermore, in step (3), the ultrasonic vibration frequency is 10 to 40 KHz, and the ultrasonic vibration power is 1000 to 5000 W.

[0015] Furthermore, in step (4), the diameter of the stainless steel shot is 0.4-6 mm, the shot peening distance is 6-18 mm, and the shot peening pressure is 2.20-2.60 MPa.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention provides a method for improving the welding structure and performance of a magnesium alloy. The prepared magnesium alloy welding zone has a uniform and dense structure, a weld joint tensile strength of 250-290 MPa, an elongation of 7.1%-9.2%, and the performance of the magnesium alloy welding zone is significantly improved.

[0018] The prior art is very easy to form a strong and regularly distributed texture in the magnesium alloy welding area, and the joint is prone to strain localization during the loading and deformation process, resulting in a significant decrease in the mechanical properties of the joint. In view of the shortcomings of the prior art, the present invention provides a method for improving the welding structure and performance of magnesium alloys. In the present invention, a small deformation hot rolling process is first used to reduce defects such as weld metal collapse, pores and looseness in the welding area and regulate the regularly distributed texture of the welding area, but the deformed weld structure is easy to separate from the matrix during use, resulting in a decrease in welding performance. Therefore, after hot rolling deformation, the present invention uses ultrasonic assisted laser remelting technology to significantly fuse the structure of the welding area and the matrix area, greatly improve the bonding strength of the welding area and the matrix, and because the ultrasonic assisted forging effect can refine the grain structure of the remelting area, the surface shot peening is finally used to mainly improve the degree of finishing of the welding area and the matrix area and reduce the crack source. Therefore, the welding structure and performance of the magnesium alloy prepared by the present invention are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a microstructure morphology of the magnesium alloy welding zone prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0021] The magnesium alloy material AZ91 designed in this embodiment is a well-known material widely used in the art.

[0022] Embodiment 1:

[0023] (1) The magnesium alloy welding sheet is polished flat, then ultrasonically cleaned in alcohol, and dried with compressed nitrogen;

[0024] (2) The cleaned magnesium alloy welding sheet is fixed on the working platform of the rolling mill, and then hot-rolled with a small deformation, and then the oxide layer is removed. The hot rolling temperature is 350°C, the rolling reduction is 20%, and the hot rolling is cooled at a cooling rate of 30°C / s. After cooling to 180°C, it is put into the furnace for heat preservation. After heat preservation for 40 minutes, it is cooled to room temperature with the furnace;

[0025] (3) Under an argon protective atmosphere, ultrasonic-assisted laser remelting was performed on the surface of the magnesium alloy welding sheet workpiece obtained in step (2), with an argon flow rate of 15 L / min, a laser power of 1500 W, a spot diameter of 4 mm, a scanning speed of 6 mm / s, an overlap rate of 50%, an ultrasonic vibration frequency of 20 KHz, and an ultrasonic vibration power of 2000 W;

[0026] (4) The surface of the magnesium alloy welded sheet workpiece obtained in step (3) is surface strengthened by using a shot peening device, wherein the diameter of the stainless steel shot is 2 mm, the shot peening distance is 8 mm, and the shot peening pressure is 2.20 MPa.

[0027] The prepared magnesium alloy welding area was characterized by microstructure and tested for mechanical properties that met national standards. Figure 1 The prepared magnesium alloy welding zone has uniform and dense structure, the tensile strength of the welded joint is 290MPa, and the elongation is 9.2%.

[0028] Embodiment 2:

[0029] Basically the same as Example 1, but with the following changes: the hot rolling temperature in step (1) is 420°C.

[0030] The mechanical properties of the prepared magnesium alloy welding area were tested to meet the national standard requirements. The tensile strength of the welded joint was 250 MPa and the elongation was 7.1%.

[0031] Embodiment 3:

[0032] Basically the same as Example 1, but with the following changes: the laser power in step (3) is 1200W.

[0033] The mechanical properties of the prepared magnesium alloy welding area were tested to meet the national standard requirements. The tensile strength of the welded joint was 265 MPa and the elongation was 7.7%.

[0034] Embodiment 4:

[0035] Basically the same as Example 1, but with the following changes: the laser power in step (3) is 1800W.

[0036] The mechanical properties of the prepared magnesium alloy welding area were tested to meet the national standard requirements. The tensile strength of the welded joint was 273 MPa and the elongation was 8.2%.

[0037] Comparative Example 1:

[0038] (1) Grind the magnesium alloy welding sheet flat, then ultrasonically clean it in alcohol, and blow dry it with compressed nitrogen;

[0039] (2) The surface of the magnesium alloy welded sheet workpiece obtained in step (1) is surface strengthened by using a shot peening device, wherein the diameter of the stainless steel shot is 2 mm, the shot peening distance is 8 mm, and the shot peening pressure is 2.20 MPa.

[0040] The mechanical properties of the prepared magnesium alloy welding area were tested to meet the national standard requirements. The tensile strength of the welded joint was 195 MPa and the elongation was 5.8%.

[0041] Comparative Example 2:

[0042] (1) Grind the magnesium alloy welding sheet flat, then ultrasonically clean it in alcohol, and blow dry it with compressed nitrogen;

[0043] (2) The cleaned magnesium alloy welding sheet is fixed on the working platform of the rolling mill, and then hot-rolled with a small deformation, and then the oxide layer is removed. The hot rolling temperature is 350°C, the rolling reduction is 20%, and the hot rolling is cooled at a cooling rate of 30°C / s. After cooling to 180°C, it is put into the furnace for heat preservation. After heat preservation for 40 minutes, it is cooled to room temperature with the furnace;

[0044] (3) The surface of the magnesium alloy welded sheet workpiece obtained in step (2) is surface strengthened by shot peening equipment, wherein the diameter of the stainless steel shot is 2 mm, the shot peening distance is 8 mm, and the shot peening pressure is 2.20 MPa.

[0045] The mechanical properties of the prepared magnesium alloy welding area were tested to meet the national standard requirements. The tensile strength of the welded joint was 228 MPa and the elongation was 6.3%.

[0046] Comparative Example 3:

[0047] The magnesium alloy welding sheet was polished and then ultrasonically cleaned in alcohol and dried with compressed nitrogen.

[0048] The magnesium alloy welding area was tested for mechanical properties that met the national standard requirements. The tensile strength of the welded joint was 182MPa and the elongation was 5.3%.

[0049] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A method for improving the welding structure and performance of magnesium alloy, characterized in that: The specific steps include: (1) Grind the magnesium alloy welding sheet flat, then ultrasonically clean it in alcohol and blow it dry with compressed nitrogen; (2) Fix the cleaned welded sheet on the working platform of the rolling mill, then perform small deformation hot rolling, and then remove the oxide layer; (3) performing ultrasonic-assisted laser remelting on the surface of the magnesium alloy welding sheet workpiece obtained in step (2) under an argon protective atmosphere; (4) Using shot peening equipment, the surface of the magnesium alloy welded sheet workpiece obtained in step (3) is strengthened.

2. A method for improving the welding structure and performance of magnesium alloy according to claim 1, characterized in that: In step (2), the hot rolling temperature is 350-460° C., and the rolling reduction is 10-20%.

3. The method for improving the welding structure and performance of magnesium alloy according to claim 1, characterized in that: In step (2), after hot rolling, the steel is cooled at a cooling rate of 30-40°C / s, cooled to 150-200°C, and then placed in a furnace for heat preservation. After heat preservation for 40-60 minutes, the steel is cooled to room temperature in the furnace.

4. The method for improving the welding structure and performance of magnesium alloy according to claim 1, characterized in that: In step (3), the argon gas flow rate is 15 L / min, the laser power is 800-2000 W, the spot diameter is 2-6 mm, the scanning speed is 5-10 mm / s, and the overlap rate is 50%.

5. The method for improving the welding structure and performance of magnesium alloy according to claim 1, characterized in that: The ultrasonic vibration process parameters of step (3) are as follows: the ultrasonic vibration frequency is 10 to 40 kHz, and the ultrasonic vibration power is 1000 to 5000 W.

6. The method for improving the welding structure and performance of magnesium alloy according to claim 1, characterized in that: In step (4), the shot peening process parameters are as follows: the diameter of the stainless steel shot is 0.4-6 mm, the shot peening distance is 6-18 mm, and the shot peening pressure is 2.20-2.60 MPa.

7. The method for improving the welding structure and performance of magnesium alloy according to any one of claims 1 to 6, characterized in that: The tensile strength of the welded joint is 250-290 MPa, and the elongation is 7.1%-9.2%.

8. The method for improving the welding structure and performance of magnesium alloy according to claim 7, characterized in that: The magnesium alloy is AZ91.

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