Friction stir deposition repair method for magnesium alloy surface defects

Abstract

The invention provides a friction stir deposition repairing method for magnesium alloy surface defects. Comprising the following steps: step 1, checking and cleaning a defective component; 2, a to-be-repaired area is machined, and a filling material is prepared; 3, the to-be-repaired part is installed and clamped, and repairing is conducted; 4, waste materials are cleaned, and next-layer deposition repair is conducted; 5, the repairing quality and performance are inspected; and 6, after repairing is completed, surface treatment and coating are conducted on the part. Based on the solid-phase characteristics of the magnesium alloy, the AFSD technology is used for repairing the surface defects of the magnesium alloy, and the defects such as cracks and air holes are avoided; according to the AFSD repairing method, under the condition that the structure property of the feeding material is not changed, the influence on the base material can be effectively avoided, and compared with other repairing methods, the residual stress and the thermal deformation degree after AFSD repairing are low.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of metal deposition additive manufacturing; in particular, it relates to a magnesium alloy surface defect repair method by friction stir deposition. BACKGROUND

[0002] Additive Friction Stir Deposition (AFSD) is an advanced processing method that combines friction stir welding and deposition additive manufacturing technology. By inserting processable material between two substrates, the additive process relies on friction heat generated by the additive material and plastic deformation heat generated by the material during the process to form a plastic material. The material is extruded by the stir head and spread into a layered structure in a certain direction. The stir head reciprocates on the initial deposition layer to continuously stack three-dimensional solid components. Compared with traditional welding methods, AFSD does not need to melt the material, but uses a high-speed rotating stir head to process the joint interface by applying axial force. This non-melting processing method can reduce the heat-affected zone and maintain the integrity and performance of the material.

[0003] Casting magnesium alloy has excellent alloy characteristics of low density and high strength, and is widely used in aerospace, rail transportation and other fields. Magnesium alloy components are usually poured into molds and solidified into shapes. However, due to the influence of the undercooling degree of the surface fine grain zone and the central equiaxed grain zone of the cast magnesium alloy, pores and hot cracks are easily formed in the near-surface region after rapid cooling, resulting in a large stress concentration in the defect area, which not only disrupts the stress balance in the area, but also increases the risk of component failure. For example, in industrial production, AZ31B cast magnesium alloy is used as a representative, and air infiltration during casting leads to defects such as pores and inclusions, which may cause crack propagation under external stress cycling, resulting in component failure. Currently, Chinese patents CN118559152A and CN117773142A, etc. have proposed methods for repairing magnesium alloy surface defects using remelting or laser melting welding, which have achieved good repair results. However, the existing repair methods lack consideration of the alloy characteristics of magnesium alloy, and magnesium alloy is not suitable for repair by welding methods, and secondary defects such as pores and cracks are easily produced during solidification.

[0004] The best choice to solve the above technical problems is the repair method of AFSD, which can effectively repair the alloy surface defects, and the strength, hardness and mechanical properties after repair are consistent with the substrate. At the same time, the additive process of friction stir deposition is a solid-state process, and its temperature range is 0.6-0.9T m , which can avoid solidification and thermal deformation problems, maintain the original structure of the material and ensure stable performance; only using solid-state materials processing avoids the generation of a large amount of impurities. SUMMARY

[0005] The purpose of the present application is to provide a magnesium alloy surface defect friction stir deposition repair method; the present application proposes a high-precision rapid repair method using friction stir deposition technology for defects on the surface of cast magnesium alloy components, overcomes the problem of difficult repair of surface defects of cast magnesium alloy components, realizes rapid high-quality repair while saving manufacturing costs.

[0006] The present application is realized by the following technical solutions:

[0007] The present application relates to a magnesium alloy surface defect friction stir deposition repair method, comprising the following steps:

[0008] Step 1, inspect and clean the defective component;

[0009] Step 2, detect the range of damaged areas, and plane or cut off the damaged surface of the component in a regular pattern to remove damaged or worn materials and process the repair area, and prepare the same composition of the filling material as the defective component to be repaired;

[0010] Step 3, install and clamp the component to be repaired, start the repair equipment (produced by Jiangsu Jitaimai Intelligent Technology Co., Ltd.), and perform repair; wherein the repair equipment is a 3-axis free friction stir forming machine tool, and the spindle speed range is 10-5000r / min;

[0011] Step 4, clean the waste left by the previous layer of repair, and then perform the next layer of deposition repair;

[0012] Step 5, inspect the repair quality and performance;

[0013] Step 6, after the repair is completed, perform surface treatment and coating on the component to improve corrosion resistance and beautify the appearance.

[0014] Preferably, in step 1, the specific steps of cleaning are:

[0015] Step 1.1, use a handheld sander to polish the surface of the defective component until it is smooth;

[0016] Step 1.2, use acetone or 99% anhydrous ethanol to wipe the surface until it is smooth and clean.

[0017] Preferably, in step 2, the specific steps of processing the repair area are:

[0018] Step 2.1, determine the depth of the bevel based on the deepest defect on the surface of the cast magnesium alloy as the processing reference point;

[0019] Step 2.2, a groove is machined at the defect position by using a ball end mill, the groove is in the shape of V or T, the width of the groove is d = 2 mm, and the depth of the groove is greater than the width of the groove.

[0020] Preferably, in step 2, the filling material is a 10 mm * 10 mm * 100 mm bar, the elements of which are consistent with the elements of the component to be repaired, and the groove is kept smooth and bright. The cross-sectional size of 10 * 10 mm is selected for repair, and the bar can be fully utilized, with a softened volume ≈ deposited volume.

[0021] Preferably, in step 3, the specific steps of the repair are as follows:

[0022] Step 3.1, adjust the stirring head with the positioning device, the feeding material should not exceed the plane of the stirring head to prevent breakage; it should be flush with the plane of the stirring head or 1-2 mm inside, and the stirring head is made of heat-resistant steel, which has the advantages of high hardness, wear resistance, heat resistance, strength and toughness. Even at 1000℃, it still has high hardness; the positioning device is a photoelectric sound Z-axis setter, and the Z-axis moves at ×10 when adjusting the distance.

[0023] Step 3.2, turn on the water cooling device and check for leaks after 10 seconds of operation;

[0024] Step 3.3, start the friction stir deposition equipment and turn on the hydraulic device, and preheat the machine;

[0025] The optimal preheating temperature of the hydraulic device is 20℃, and the stepwise preheating method is different from the traditional direct preheating. The temperature rises slowly at the starting stage, and then quickly reaches the maximum value, which can better make the magnesium alloy bar reach the softening temperature in a short time and flow regularly in a vortex shape along the center to the periphery.

[0026] Step 3.4, vertically align the stirring head with the center of the repair area, set the start-stop coordinates (X, Y), the rotation speed S, the horizontal movement rate V, and the pressing amount F, and start the program. The high-speed rotation of the stirring head and the friction with the base material generate heat to soften the solid feeding material; the stirring head rotation speed is 350-450 r / min; within this speed range, a good deposition repair layer can be formed, and the material softening rate per unit time is approximately linearly related to the rotation speed.

[0027] Step 3.5, move the stirring head according to the specified repair path by shaking the controller, and input the G01 instruction code to control the hydraulic device to press the material; the movement rate of the stirring head is 1.5 mm / s, and the upper and lower limit distance of the hydraulic rod is 95-100 mm.

[0028] Preferably, in step 3.3, the preheating mode is stepwise preheating, and the temperature rising rate of the hydraulic device approximately satisfies a sinusoidal function relationship with the preheating time; the downward pressing amount of the hydraulic device is 50 mm / min, and the pressure is 4-5 MPa. The downward pressing amount (50 mm / min) of the hydraulic device can effectively control the generation of flash of the deposited layer and realize better combination of the filling material and the defects.

[0029] Preferably, in step 4, the specific steps are as follows:

[0030] Step 4.1: after the first layer of repair is completed, stopping for 10 s, controlling the stirring head to be lifted by 2 mm, adjusting the start and end point coordinates in the program setting, keeping the repair length unchanged, and keeping the height of the repair layer head and tail the same;

[0031] Step 4.2: repeating step 4.1 until the defect area is completely filled, and the repair height is greater than the original surface of the magnesium alloy casting by 0.5-1 mm, and then the process is completed.

[0032] Preferably, in step 4.1, during the repair of each layer, the temperature of the stirring head is appropriately lowered by continuously blowing air with an air flow of 20-30 L / min, the surface magnesium alloy oxide is quickly cleaned, and then the next layer of repair is performed.

[0033] The friction stir deposition repair method disclosed by the application has a faster repair rate, does not need to add a protective gas during the repair process, and the utilization rate of the filling material can reach more than 95%.

[0034] Preferably, in step 5, the inspection steps are as follows:

[0035] Step 5.1: directly observing whether there is an obvious defect on the surface of the repaired magnesium alloy component;

[0036] Step 5.2: taking a 7 mm*8 mm*8 mm sample at the center of the repair area, grinding it with 240-2000 mesh sandpaper, and then observing the material flowability and whether there is a pre-opening groove after precision polishing and placing it under an optical microscope;

[0037] Step 5.3: taking a tensile sample at the center of the repair area and taking a tensile sample of the base material of the magnesium alloy component, respectively testing the tensile strength, comparing the changes of the tensile properties before and after the repair, and evaluating the tensile strength after the repair.

[0038] Step 5.4: taking a cross-section SEM sample at the center of the repair area, observing the microstructure of the magnesium alloy after the repair, whether there is a pore, a crack, and an oxidation phase, and evaluating the quality of the friction stir repair.

[0039] The casting magnesium alloy defect is repaired by the friction stir deposition, and the tensile strength can reach more than 92% of the base material, the interface bonding performance is good, and no impurity and insufficient bonding phenomenon is found in the bonding area; the second phase is generated in the repair area and is distributed in the crystal to play a precipitation strengthening role, the second phase is less distributed at the grain boundary, and a small amount of oxide phase is generated.

[0040] The present application has the following advantages:

[0041] (1) The present application relates to a method for repairing magnesium alloy surface defects by friction stir deposition, which is based on the solid phase characteristics and uses AFSD technology to complete the repair of magnesium alloy surface defects, avoiding the generation of defects such as cracks and pores; the AFSD repair method involved in the present application can effectively avoid the influence on the base material without changing the organization and performance of the feeding material, and the residual stress and thermal deformation degree after AFSD repair are lower compared with other repair methods.

[0042] (2) The present application relates to a method for repairing magnesium alloy surface defects by friction stir deposition, which does not require additional fillers or powders, but only uses solid magnesium alloy materials for processing, reducing the need for impurities and subsequent processing. Compared with existing crack repair fillers, the alloy density of magnesium alloy is lower, and as a cladding material, it also has a lower melting point and lower hardness. The relatively soft material properties are beneficial to the flow and bonding of the repair area material, buffer the stress of the repair area, and avoid the secondary initiation of cracks caused by stress concentration in the repair area. On the other hand, during the repair process, the local metal in the repair area is highly plasticized by friction heat and is subjected to thermal stirring, resulting in dynamic recrystallization to form fine equiaxed crystal structure, which also avoids the generation of secondary cracks in the area, and the strength after repair is higher, and the comprehensive performance is better than other repair methods.

[0043] (3) The friction stir deposition repair technology described in the present application is mainly used for repairing magnesium alloy defects, which is obviously different from traditional large-thickness friction stir deposition additive manufacturing.

[0044] (4) The friction stir repair described in the present application is mainly used for repairing planar defects, which is suitable for industrial production; for complex spatial structure defects of curved surface type, flexible equipment such as robots can also be used for repair, which has great engineering application prospect and can be widely used in aerospace, automobile manufacturing and energy field repair. The repair of super-large complex components such as hollow components and honeycomb components has obvious technical advantages. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The flow chart of the friction stir deposition repair method for the magnesium alloy surface defects involved in the present application;

[0046] Figure 2A schematic diagram of a groove shape effect of the AZ31B magnesium alloy defect processing in the present application;

[0047] Figure 3 A schematic diagram of the AZ31B magnesium alloy defect friction stir deposition repair effect in the present application;

[0048] Figure 4 A schematic diagram of the step preheating curve in the embodiment 1 and the embodiment 2 of the present application;

[0049] Figure 5 A schematic diagram of the SEM micrograph of the cross section of the AZ31B after repair in the present application. DETAILED DESCRIPTION

[0050] The present application will be described in detail below with specific examples. It should be noted that the following examples are only further illustrations of the present application, and the protection scope of the present application is not limited to the following examples.

[0051] Embodiment 1

[0052] This embodiment relates to a repair method for repairing near-surface defects of AZ31B magnesium alloy by friction stir deposition. The substrate to be repaired is selected as AZ31B magnesium alloy, and the chemical composition is shown in Table 1.

[0053] Table 1

[0054] Mg Al Zn Mn balance 93％ 3％ 1％ 0.3％ 2％

[0055] As shown in Figure 1 , the specific steps are as follows:

[0056] S1, the surface of the AZ31B magnesium alloy substrate to be repaired is flattened with a milling cutter, the surface of the substrate is cleaned with acetone to remove oil stains, the oxide film and impurities around the defects of the substrate are polished with sandpaper, and then the substrate is cleaned with 99% anhydrous ethanol;

[0057] S2, the substrate around the defects is milled about 2mm in the thickness direction with a milling cutter, so that the cross section of the substrate is V-shaped depth groove, the depth is about 2mm, the AZ31B magnesium alloy substrate has a thickness of 15mm, the tensile strength of the substrate is 290Mpa measured by a universal tensile testing machine, the defects are near-surface crack defects, the crack length is 3.5mm, and the depth is 2mm, as shown in Figure 2 ;

[0058] S3, the four corners of the AZ31B magnesium alloy substrate to be repaired are positioned and clamped with a workbench clamp, ensuring that the stirring head is perpendicular to the substrate plane. Wire cutting is used to repair the magnesium alloy rod, which is about 100 mm long and has a diameter consistent with the feeding port of the stirring head, about 9-10 mm. After processing, the repaired rod is slowly pushed into the cavity of the stirring head, and the hydraulic rod is slowly lifted upwards. When the rod is flush with the plane of the stirring head, stop and fix the position of the rod. Set the up and down movement limits of the hydraulic rod, and prevent the hydraulic rod from contacting the substrate to prevent tool breakage;

[0059] S4, the extrusion center of the stirring head is aligned above the defect of the AZ31B magnesium alloy to be repaired, leaving a gap of 0.5-1 mm, and the water cooling device is turned on. Import the device program source code. In this embodiment, the inner diameter of the stirring head is 5 mm and the outer diameter is 20 mm. Set the process parameters as follows: the rotation speed of the friction extrusion stirring head is 400 r / min, the axial pressure of the hydraulic rod is 4.5 Mpa, the pushing speed is 2 mm / s, and the workbench travel speed is 1.5 mm / s;

[0060] S5, the stirring head is lowered to the target distance, the program is started, and the stirring head is preheated for 15 s after contacting the substrate, and then moved. The step preheating curve is as shown in Figure 4 . The heat generated by the rotation of the stirring head converts the metal rod into a viscous plastic fluid, which fills the gap between the stirring head and the substrate and the reserved groove under the extrusion of the hydraulic rod. After the workbench moves according to the set path, the initial deposition layer is completed. Repeat the above process to complete the defect repair. After the repair is completed, the stirring head is moved up and the device is turned off. The AZ31B magnesium alloy substrate to be repaired is removed, the remaining waste material on the surface of the repair is removed with a steel brush, the burrs are polished with sandpaper, and the repaired part is polished to the same height as the original substrate. The repaired cross section is cut and observed with SEM. The repair layer is well connected with the substrate, and there is no insufficient fusion area, as shown in Figure 3 .

[0061] The tensile strength of the repaired part is 266 Mpa, which is 90.3% of the substrate.

[0062] Example 2

[0063] This embodiment relates to a repair method for repairing near-surface defects of AZ40M magnesium alloy by friction stir deposition additive repair. The substrate to be repaired is AZ40M magnesium alloy, and the chemical composition is shown in Table 2. The left graph is a V-shaped groove, and the right graph is a T-shaped groove.

[0064] Table 2

[0065] Mg Al Zn Mn balance 3％-4％ 0.2％-0.8％ 0.15％-0.5％

[0066] As shown in Figure 1 , the specific steps are as follows:

[0067] S1, the surface of the AZ40M magnesium alloy substrate to be repaired is flattened with a milling cutter, the surface of the substrate is cleaned of oil with acetone, the oxide film and impurities around the defects of the substrate are polished with sandpaper, and then the substrate is cleaned with 99% anhydrous ethanol.

[0068] S2, about 3mm of the substrate around the defects is milled in the thickness direction with a milling cutter, so that the cross section of the substrate is T-shaped and the depth of the groove is about 3mm. The AZ40M magnesium alloy substrate has a thickness of 15mm, the tensile strength of the substrate is 250Mpa measured by a universal tensile testing machine, and the defects are near-surface crack defects with a crack length of 5mm and a depth of 1.8mm.

[0069] S3, the AZ40M magnesium alloy substrate to be repaired is clamped with a workbench clamp after positioning the four corners, and the stirring head is perpendicular to the plane of the substrate. The wire-cutting magnesium alloy rod for repair is about 100mm long and the diameter is consistent with the feeding port of the stirring head, about 9-10mm. The processed repair rod is slowly pushed into the cavity of the stirring head, and the hydraulic rod is slowly lifted upwards. When the rod is flush with the plane of the stirring head, stop and fix the position of the rod. Set the up and down movement limit of the hydraulic rod, and the hydraulic rod cannot contact the substrate to prevent the tool from being hit.

[0070] S4, the extrusion center of the stirring head is aligned above the AZ40M magnesium alloy defect to be repaired, leaving a gap of 0.5-1mm, and the water cooling device is turned on. Import the device execution program source code. In this example, the inner diameter of the stirring head is 5mm and the outer diameter is 20mm. Set the process parameters as follows: the rotation speed of the friction extrusion stirring head is 350r / min, the axial pressure of the hydraulic rod is 4Mpa, the pushing speed is 1.5mm / s, and the workbench travel speed is 1.5mm / s.

[0071] S5, the friction stirring head is lowered to the target distance, the program is started, and the stirring head is preheated for 15s after contacting the substrate and then starts to move. The step preheating curve is shown in Figure 4 The heat generated by the rotation of the stirring head converts the metal rod into a viscous plastic fluid, which fills the gap between the stirring head and the substrate and the reserved groove under the extrusion action of the hydraulic rod. After the workbench moves according to the set path, the initial deposition layer is completed. Then repeat the above process to complete the defect repair. After the repair is completed, the stirring head is moved upwards and the device is turned off. The AZ40M magnesium alloy substrate to be repaired is removed, the remaining waste material on the surface of the repair is removed with a steel brush, the burrs are polished with sandpaper, and the repaired part is polished to the same height as the original substrate. The repair cross section is cut and observed with SEM. The repair layer is well connected with the substrate, and no insufficient fusion area is found, as shown in Figure 5 The tensile strength of the repaired part is 224Mpa, which is 89.6% of the substrate.

[0072] The application is based on its solid phase characteristics, and uses the AFSD technology to complete the repair of the surface defects of the magnesium alloy, so as to avoid the generation of defects such as cracks and pores; the AFSD repair method involved in the application can effectively avoid the influence on the base material without changing the organizational properties of the feeding material, and compared with other repair methods, the residual stress and the degree of thermal deformation after the AFSD repair are both lower.

[0073] The application relates to a method for repairing surface defects of a magnesium alloy by using friction stir deposition, which does not need additional fillers or powders, but only needs to use solid magnesium alloy material processing, thereby reducing the demand for impurities and subsequent processing. Compared with existing crack repair fillers, the magnesium alloy has lower alloy density, lower melting point as a cladding material, and lower hardness, and the relatively soft material attribute is beneficial to the flow and combination of the material in the repair area, buffers the stress in the repair area, avoids the secondary generation of cracks caused by stress concentration in the repair area. On the other hand, during the repair process, the local metal in the repair area is highly plasticized under the influence of friction heat and is subjected to thermal stirring, dynamic recrystallization occurs to form fine equiaxed crystal structure, the generation of secondary cracks in the repair area is also avoided, and the strength after the repair is higher, and the comprehensive performance is better than that of other repair methods.

[0074] The specific embodiments of the application are described above. It should be understood that the application is not limited to the above specific embodiments, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essence of the application.

Claims

1. A method for repairing surface defects of magnesium alloys by friction stir deposition, characterized in that, Includes the following steps: Step 1: Inspect and clean the defective components; Step 2: Inspect the extent of the damaged area, plan or cut the damaged surface of the component in a regular shape to remove the damaged or worn material, process the area to be repaired, and prepare a filler material with the same composition as the defective component to be repaired. Step 3: Install and clamp the part to be repaired, start the repair equipment, and carry out the repair; wherein, the repair equipment is a friction stir sheet metal forming machine tool with 3-axis degrees of freedom, and the spindle speed range is 10 to 5000 r / min; Step 4: Clean up the waste material left over from the previous layer of repair before proceeding with the next layer of deposition repair; Step 5: Inspect the quality and performance of the repair; Step 6: After the repair is completed, perform surface treatment and coating on the parts.

2. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 1, characterized in that, In step 1, the specific steps of cleaning are as follows: Step 1.1: Use a handheld grinder to grind the surface of the defective component until it is smooth; Step 1.2: Wipe the surface with acetone or 99% anhydrous ethanol until it is smooth and free of dirt.

3. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 1, characterized in that, In step 2, the specific steps for processing the area to be repaired are as follows: Step 2.1: Determine the depth of the bevel by using the deepest defect on the surface of the cast magnesium alloy as the machining reference point; Step 2.2: Use an end mill to machine the bevel at the defect location. The bevel shape is V-shaped or T-shaped, the width of the bevel is d = 2mm, and the bevel depth is greater than the bevel width.

4. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 1, characterized in that, In step 2, the filling material is a 10mm*10mm*100mm bar, whose elements are consistent with those of the defective component to be repaired, and the bevel is kept bright and smooth.

5. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 1, characterized in that, In step 3, the specific steps of the repair are as follows: Step 3.1: Adjust the stirring head using the positioning device. The feed material should not exceed the plane of the stirring head to prevent breakage; it should be flush with the plane of the stirring head or recessed by 1-2 mm. The stirring head is made of heat-resistant steel. Step 3.2: Turn on the water cooling device and check for cooling water leaks after running for 10 seconds. Step 3.3: Start the agitation and friction deposition equipment and turn on the hydraulic device to preheat the machine; Step 3.4: Align the stirring head vertically with the center of the repair area, and set the start and stop coordinates (X,Y), rotation speed S, lateral speed V, and downward pressure F. Start the program to start the high-speed rotation of the stirring head and the heat generated by the friction between the stirring head and the substrate to soften the solid feed material; wherein, the stirring head rotation speed is 350-450 r / min. Step 3.5: Shake the controller to move the stirring head along the specified repair path, and input the G01 command code to control the hydraulic device to press down the material; the moving speed of the stirring head is 1.5mm / s, and the upper and lower limit distance of the hydraulic rod is 95~100mm.

6. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 5, characterized in that, In step 3.3, the preheating method is stepped preheating, and the temperature rise rate of the hydraulic device approximately satisfies a sine function relationship with the preheating time; the downward pressure of the hydraulic device is 50 mm / min, and the pressure is 4 to 5 MPa.

7. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 1, characterized in that, Step 4, the specific steps are as follows: Step 4.1: After the first layer of repair is completed, pause for 10 seconds, raise the stirring head by 2mm, change the start and end coordinates in the program settings, keep the repair length unchanged, and keep the height of the beginning and end of the repair layer the same. Step 4.2: Repeat step 4.1 until the defective area is completely filled. The repair height should be 0.5 to 1 mm greater than the original magnesium alloy casting surface.

8. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 7, characterized in that, In step 4.1, during the repair process of each layer, use an air gun with an air flow rate of 20-30L / min to continuously blow air to appropriately reduce the temperature of the stirring head, quickly clean the magnesium alloy oxide on the surface, and then proceed to the next layer of repair.

9. The method for repairing surface defects of magnesium alloys by friction stir deposition as described in claim 1, characterized in that, In step 5, the specific steps of the inspection are as follows: Step 5.1: Directly observe whether there are obvious defects on the surface of the repaired magnesium alloy component; Step 5.2: Take a sample from the center of the repair area, measuring 7mm*8mm*8mm, grind it with 240-2000 grit sandpaper, then polish it finely and place it under an optical microscope to observe the material flowability and the presence of pre-opened bevels. Step 5.3: Take a tensile specimen from the center of the repair area and a tensile specimen from the magnesium alloy component base material, test the tensile strength of each, compare the changes in tensile properties before and after repair, and evaluate the tensile strength after repair. Step 5.4: Take a SEM sample of the central cross-section of the repaired area to observe the microstructure of the magnesium alloy after repair, and to determine whether there are pores, cracks and oxide phases, and to evaluate the quality of friction stir repair.

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