A method for repairing surface defects of a magnesium alloy and application thereof

Abstract

The application relates to a magnesium alloy surface defect repairing method and belongs to the technical field of surface repairing engineering. The magnesium alloy surface region is preprocessed, high-strength composite powder is used, and ultrasonic cold spraying is used to deposit and repair the defect region. The obtained repairing layer has high compactness, good bonding strength, and also has excellent tensile property and wear resistance.

Description

Technical Field

[0001] This invention relates to the field of defect repair engineering technology, and in particular to a method and application for repairing defects on the surface of magnesium alloys. Background Technology

[0002] Magnesium alloys are widely used in critical components such as aero-engine casings and oil pump housings due to their high specific strength and specific stiffness. However, these components are prone to defects such as scratches, dents, and corrosion pits under harsh operating conditions. Furthermore, magnesium alloys have low hardness and poor wear resistance, often failing due to localized crushing and wear. Therefore, remanufacturing and repair are of great value.

[0003] For the repair of magnesium alloy aerospace components, traditional thermal repair processes such as laser cladding and argon arc welding are prone to oxidation, burning, deformation, and grain coarsening due to the heat input sensitivity of magnesium alloys and the complex structure of castings. This severely impairs dimensional accuracy and mechanical properties. Even with low heat input and protective atmospheres, critical areas such as thin walls and bolt hole edges cannot be repaired. Remedial measures such as using metal gaskets or resin filling fall far short of the required repair quality and capability. In recent years, supersonic cold spraying, as a low-temperature solid-state deposition technology, has attracted much attention due to its ability to avoid heat-affected zones. However, when applied directly, the sharp right-angled grooves and other defect edges generate shock wave effects, hindering particle deposition and compaction, resulting in porous deposits with weak bonding, and even areas without deposition. Furthermore, using pure aluminum or soft aluminum alloy powders compatible with the substrate results in repaired areas with significantly lower hardness and wear resistance than the magnesium matrix, becoming a performance bottleneck.

[0004] Therefore, there is an urgent need to develop a method for repairing surface defects in magnesium alloys that can take into account bonding strength, density, and improve the wear resistance of the repaired area. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and application for repairing defects on magnesium alloy surfaces that can take into account bonding strength, density and improve the wear resistance of the repaired area.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for repairing surface defects in magnesium alloys, comprising the following steps: S1. Machining the defective areas on the surface of the magnesium alloy; S2. Using supersonic cold spraying technology, composite powder is deposited onto the machined defect area until the deposited layer is higher than the magnesium alloy surface; the composite powder includes aluminum alloy powder and ceramic particles. This invention pre-treats the defective area by machining grooves or bevels with specific geometric shapes and sizes at the edges of the defect in the substrate to be repaired. The treated defective area eliminates geometric features unfavorable to the deposition of composite powder particles and optimizes the flow field of the supersonic airflow. This provides a smooth transition substrate for subsequent cold-sprayed composite powder, allowing powder particles to deposit smoothly at the root of the bevel, guiding the composite powder particle flow to fill smoothly and enhance bonding, avoiding "no-deposition zones." Subsequently, a composite powder of ceramic particles and aluminum alloy powder is used as the repair material, with the addition of ceramic particles significantly improving the wear resistance of the repair layer. The composite powder is then deposited on the optimized defective area using supersonic cold-air spraying technology, and post-processing restores its dimensions. Supersonic cold spraying allows the entire process to be carried out at temperatures far below the material's melting point, completely avoiding thermal defects such as oxidation, burn-off, phase transformation, and thermal deformation caused by traditional thermal repair processes. Simultaneously, the intense plastic deformation caused by supersonic impact achieves high bonding strength between the particles and the substrate, forming a repair layer with high bonding strength and good density.

[0007] In a preferred embodiment of the ceramic particles described in this invention, the ceramic particles include one or more of Al2O3, WC, and SiC, with a particle size of 5–30 μm. Using the aforementioned hard ceramic particles can significantly improve the hardness and wear resistance of the repair layer, compensating for the insufficient hardness of the magnesium alloy matrix and aluminum alloy powder.

[0008] In a preferred embodiment of the aluminum alloy powder of the present invention, the aluminum alloy powder comprises aluminum alloy, specifically one or more of 6xxx series aluminum alloys and 7xxx series aluminum alloys, with a particle size of 10-53 μm. 6xxx series and 7xxx series aluminum alloys possess both high strength and good plastic deformation capacity, ensuring compatibility and bonding strength with the magnesium alloy matrix while effectively avoiding the shortcomings in hardness and wear resistance of the repair area caused by using pure aluminum.

[0009] In a preferred embodiment of the composite powder of the present invention, the mass fraction of ceramic particles in the composite powder is 5% to 30%, preferably 10% to 20%. At this ratio, the ceramic particles can exert a significant dispersion strengthening effect, significantly improving the wear resistance of the repair layer while maintaining sufficient tensile strength to prevent brittle cracking of the cold-sprayed deposit. Excessive ceramic particle content will lead to a sharp decrease in the plasticity of the composite deposit layer, increased internal stress, and easy initiation of cracks or even spalling; insufficient content will result in limited strengthening effect, and the wear resistance of the repaired area will be difficult to meet the application requirements.

[0010] As a preferred embodiment of the supersonic cold spraying parameters described in this invention, the spraying distance is 15–30 mm, the spray gun moving speed is 50–300 mm / s, and the gas used for supersonic spraying includes one or more of nitrogen, helium, compressed air, and argon, with a gas pressure of 2.0–5.5 MPa and a gas temperature of 300–600 °C. Within the above parameter range, the powder particles can maintain a high velocity and appropriate temperature upon reaching the substrate, achieving efficient and dense deposition.

[0011] In a preferred embodiment of the magnesium alloy surface defect repair method of the present invention, the machining in step S1 includes any one or more of the following: (1) The result of a sharp angle in the vertical section of the defect area is processed into a chamfered structure in the vertical section, wherein the angle of the sharp angle is ≤100°; (2) The structure with an irregular shape in the vertical cross section in the defect area is processed into a structure with a circular arc shape in the vertical cross section.

[0012] In a preferred embodiment of the chamfering described in this invention, the chamfering angle is 30° to 80°. The chamfer is the angle between the machined bevel and the plane containing the original intact surface of the part. Within this range, the gentle bevel of the defect edge can effectively guide the supersonic gas-powder flow smoothly into the bottom of the defect, eliminate the shock wave effect caused by sharp right angles, and avoid "deposition-free zones" and coating voids.

[0013] As a preferred embodiment of the processing described in this invention, after the deposited layer in step S2 is higher than the magnesium alloy surface, the deposited layer higher than the magnesium alloy surface is processed until it is flush with the magnesium alloy surface, thereby obtaining the repaired magnesium alloy; the processing method includes any one of milling, grinding, and polishing. This type of processing method can accurately restore the geometric dimensions and surface integrity of the repaired area, meeting the assembly and service requirements of aerospace components.

[0014] As a preferred embodiment of the processing described in this invention, the composite powder is prepared by mixing and ball milling the aluminum alloy and the ceramic powder for 20-60 min.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention improves the flow field distribution of supersonic airflow and particles in defective areas of magnesium alloys by pre-processing the defective areas. Combined with high-strength aluminum alloy and ceramic particle composite powder, the microhardness and wear and corrosion resistance of the repaired area are significantly enhanced. Simultaneously, the entire repair process is conducted in a low-temperature environment, avoiding the risk of thermal damage to the magnesium alloy. Attached Figure Description

[0016] Figure 1The image shows a vertical cross-sectional view of the magnesium alloy surface in Example 1, where A is the vertical cross-section of the surface scratch and B is the vertical cross-section after being machined into a 45° chamfer. Detailed Implementation

[0017] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0018] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0019] Example 1 One embodiment of the magnesium alloy surface defect repair method of the present invention is as follows: S1. Spherical 6061 aluminum alloy powder with an average particle size of 30 μm and irregularly shaped Al2O3 hard ceramic powder with an average particle size of 10 μm are mixed and ball-milled for 60 min to obtain composite powder. The mass fraction of 6061 aluminum alloy is 90%, and the mass fraction of Al2O3 is 10%.

[0020] S2. Take the ZM6-T6 magnesium alloy casing. The surface defect is a scratch 1 mm deep and 2 mm wide. Figure 1 As shown in -A, a miniature conical grinding wheel is used to machine the defect into a vertical cross-section with a 45° chamfer, as follows. Figure 1 -B shows the area after cleaning with acetone.

[0021] S3. Using nitrogen as the working gas, supersonic cold spraying technology is used to deposit composite powder onto the processed defect area. The gas pressure is set to 5.0 MPa, the gas temperature to 600℃, the spraying distance to 30 mm, and the spray gun moving speed to 200 mm / s for deposition repair until the coating is about 0.2 mm higher than the magnesium alloy substrate.

[0022] S4. Use a precision CNC milling machine to mill the repair area until it is flush with the surface of the magnesium alloy, and obtain the repaired magnesium alloy.

[0023] Example 2 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that the composite powder contains 95% aluminum alloy by mass and 5% Al2O3 by mass.

[0024] Example 3 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that the composite powder contains 80% aluminum alloy by mass and 20% Al2O3 by mass.

[0025] Example 4 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that the composite powder contains 70% aluminum alloy by mass and 30% Al2O3 by mass.

[0026] Example 5 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that in step S2, a micro conical grinding wheel is used to process the defect into a vertical cross-section with a chamfer of 80°.

[0027] Example 6 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that in step S2, a micro conical grinding wheel is used to process the defect into a vertical cross-section with a chamfer of 60°.

[0028] Example 7 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that the surface defect is a countersunk hole structure with a depth of 10 mm and a width of 10 mm. A micro conical grinding wheel is used to process the defect into a vertical cross-section with a chamfer of 45°.

[0029] Example 8 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that the surface defect cross-section is an irregular shape, and a micro conical grinding wheel is used to process the defect into a structure with a circular arc-shaped vertical cross-section.

[0030] Example 9 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that the composite powder is 7075 aluminum alloy powder and Al2O3 particles.

[0031] Example 10 This invention provides an embodiment of a method for repairing surface defects in magnesium alloys. The difference between this embodiment and Embodiment 1 is that the composite powder is 7075 aluminum alloy powder and WC particles.

[0032] Comparative Example 1 This invention provides a comparative example of a method for repairing surface defects in magnesium alloys. The only difference between this comparative example and Example 1 is that no ceramic particles are added; only 7075 aluminum alloy powder is used for spraying.

[0033] Comparative Example 2 A comparative example of a method for repairing defects on the surface of magnesium alloys. The only difference between this comparative example and Example 1 is that the defective area is not machined, but directly sprayed with composite powder.

[0034] Comparative Example 3 A comparative example of a method for repairing defects on the surface of magnesium alloys. The only difference between this comparative example and Example 1 is that the defective area is not machined, ceramic particles are not used for composite, and 6061 aluminum alloy powder is directly sprayed onto the defective area.

[0035] Comparative Example 4 A comparative example of a method for repairing surface defects in magnesium alloys. The only difference between this comparative example and Example 1 is that the surface defect is a countersunk hole structure with a depth of 10 mm and a width of 10 mm, and no mechanical pretreatment is performed on the defect area.

[0036] Comparative Example 5 A comparative example of a method for repairing surface defects in magnesium alloys. The only difference between this comparative example and Example 1 is that aluminum metal powder is used instead of 6061 aluminum alloy powder.

[0037] Example of effect This example examines the performance of the repair layer after repairing surface defects in magnesium alloys according to the above embodiments and comparative examples. The repaired samples were cut, inlaid, polished, and etched to prepare metallographic specimens. Cross-sectional metallographic analysis was performed on the reinforced repaired specimens, and the test results are shown in Table 1.

[0038] Table 1 As shown in Table 1, the magnesium alloy surface defect repair method of the present invention, by combining pre-processing of the defect area with high-strength composite powder, can obtain a repair layer with high density, high bonding strength, strong wear resistance, high tensile strength, and high hardness. Without pre-processing, the density and bonding strength of the repair layer will decrease; without using the composite powder of the present invention as the repair layer, the wear resistance, tensile strength, and hardness of the repair layer will decrease.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for repairing surface defects in magnesium alloys, characterized in that, Includes the following steps: S1. Machining the defective areas on the surface of the magnesium alloy; S2. Using supersonic cold spraying technology, composite powder is deposited onto the machined defect area until the deposited layer is higher than the magnesium alloy surface; the composite powder includes aluminum alloy powder and ceramic particles.

2. The method for repairing surface defects of magnesium alloys as described in claim 1, characterized in that, The ceramic particles include one or more of Al2O3, WC, and SiC, and the particle size of the ceramic particles is 5~30 μm.

3. The method for repairing surface defects of magnesium alloys as described in claim 1, characterized in that, The aluminum alloy powder comprises an aluminum alloy, and the particle size of the aluminum alloy powder is 10~53 μm.

4. The method for repairing surface defects of magnesium alloys as described in claim 1, characterized in that, The mass fraction of ceramic particles in the composite powder is 5% to 30%.

5. The method for repairing surface defects of magnesium alloys as described in claim 4, characterized in that, The mass fraction of ceramic particles in the composite powder is 10% to 20%.

6. The method for repairing surface defects of magnesium alloys as described in claim 1, characterized in that, The parameters for the supersonic cold spraying are: spraying distance of 15~30 mm, spray gun moving speed of 50~300 mm / s; the gas used for supersonic spraying includes one or more of nitrogen, helium, compressed air, and argon, the gas pressure is 2.0~5.5 MPa, and the gas temperature is 300~600℃.

7. The method for repairing surface defects of magnesium alloys as described in claim 1, characterized in that, In step S1, the machining includes any one or more of the following: (1) The structure with a sharp angle in the vertical section of the defect area is processed into a structure with a chamfered vertical section, wherein the angle of the sharp angle is ≤100°; (2) The structure with an irregular shape in the vertical cross section in the defect area is processed into a structure with a circular arc shape in the vertical cross section.

8. The method for repairing surface defects of magnesium alloys as described in claim 7, characterized in that, The chamfer angle is 30°~80°.

9. The method for repairing surface defects of magnesium alloys as described in claim 1, characterized in that, The process also includes processing the deposited layer above the magnesium alloy surface after the deposited layer in step S2 is above the magnesium alloy surface until it is flush with the magnesium alloy surface, thus obtaining the repaired magnesium alloy; the processing method includes any one of milling, grinding, and polishing.

10. The method for repairing surface defects of magnesium alloys as described in claim 1, characterized in that, The composite powder is prepared by mixing the aluminum alloy powder and the ceramic powder and ball milling for 20-60 min.

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