Low-stress composite repairing process for magnesium alloy casting defects

Abstract

The invention provides a magnesium alloy casting defect low-stress composite repair process, and relates to the technical field of magnesium alloy welding repair. The process comprises the steps that the defective position of the surface of the casting is filled with a filling material, a filling area is manufactured, and the filling material is consistent with the casting in material; melting the filling area with a laser beam to form a repairing area; and after the repairing area is solidified, a friction head is used for conducting friction on the repairing area to form a repairing softening layer, meanwhile, the friction head conducts secondary repairing on the repairing area, and the repaired casting is obtained. Firstly, the defect surface of the casting is melted through a laser beam, the pertinence is high, the precision of a repairing position is higher, then a repairing area is rubbed through a friction head to form a repairing softening layer, and when the friction head conducts extrusion repairing on the repairing softening layer in the advancing direction, residual stress of the repairing area can be effectively removed; and the stress deformation of the repair area caused by repair of the filling material is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloy welding repair, and in particular to a low-stress composite repair process for magnesium alloy casting defects. Background Art

[0002] As the lightest known metal structural material, magnesium alloy has the characteristics of high specific strength, high specific stiffness, excellent shock absorption, excellent machinability, good electromagnetic shielding and easy recycling, and has been applied to many fields such as 3C electronics, aerospace, transportation, petrochemical industry, etc. Among them, cast magnesium alloy is the most widely used field of magnesium alloy materials, accounting for more than 80% of magnesium alloy products.

[0003] However, due to the special properties of magnesium alloy materials, there are inevitable problems in engineering applications, the most serious of which is casting defects, which seriously restrict its application development. That is, magnesium has high chemical activity and is easily oxidized and burned during the smelting process. During the solidification process, it is easy to have defects such as looseness, segregation, pores, inclusions, and cold shuts. The above defects will seriously affect the quality of castings, reduce the mechanical properties of castings, and even cause the castings to break during use.

[0004] At present, the most effective way to solve magnesium alloy casting defects is defect repair. The traditional tungsten electrode oxidation repair method is the main defect repair method, which is to melt and solidify the casting defect position to achieve the repair purpose.

[0005] However, the argon tungsten arc oxidation repair method has low speed and large heat input, resulting in a wide repair area and heat-affected zone. Moreover, the repaired castings have defects such as coarse grains, large residual stress, severe deformation, and poor joint performance. Summary of the invention

[0006] One purpose of the present specification is to provide a low-stress composite repair process for magnesium alloy casting defects, which can overcome the above-mentioned defects of the traditional tungsten inert gas arc oxidation repair process.

[0007] This specification solves the technical problem by adopting the following technical solutions:

[0008] This specification provides a low stress composite repair process for magnesium alloy casting defects, which mainly includes the following steps:

[0009] Filling a filling material into a defective position on the surface of the casting to obtain a filling area, wherein the filling material is consistent with the material of the casting;

[0010] Melting the filling area with the laser beam to form a repair area;

[0011] After the repair area solidifies, the repair area is rubbed with a friction head to form a repair softened layer. At the same time, the friction head performs secondary repair on the repair area to obtain a repaired casting.

[0012] In this specification, the defective position on the casting surface and the filling material may not be melted at the same time, that is, the filling material may be melted and then filled into the melted defective position, and the above-mentioned effect may also be achieved.

[0013] In this specification, before a defective position on the surface of a casting is melted by a laser beam, the defect type can be determined by X-ray flaw detection or ultrasonic flaw detection, and the size of the defect can be confirmed.

[0014] Specifically, it can be confirmed that the casting has point defects on the surface, such as small pinhole defects; it can also be confirmed that the casting has internal volume defects, such as large pores, cold shut and other defects.

[0015] In this specification, before the filling area is prepared, the surface or internal volume defects of the casting can be excavated to remove the oxide film formed on the defect surface, or to remove the oil stains and foreign matter on the surface. Specifically, the cleaning can be carried out by mechanical methods.

[0016] In this specification, after the above excavation treatment, the repair should be carried out within 24 hours, that is, the repaired casting should be produced within 24 hours. If it exceeds 24 hours, the oxide film of the excavated area should be cleaned, and then the above area should be cleaned with alcohol or acetone, and the repair can be carried out after drying.

[0017] In this specification, during the entire repair process, inert gases such as argon and helium are used to protect the filling area, the repair area, and the repaired softened layer. The inert gas should cover the area with a temperature higher than 250°C to prevent the above-mentioned area from being rapidly oxidized during the repair process, thereby affecting the repair process. Specifically, before repair, the inert gas should be delivered to the area to be repaired for more than 3 seconds, and after the repaired casting is obtained, the inert gas should continue to be delivered for no less than 5 seconds.

[0018] In this specification, before melting the repair area with a laser beam, the following steps are also included:

[0019] Determine the size of the area to be repaired;

[0020] The repair path of the laser beam on the area to be repaired is determined according to the size of the area to be repaired, the shape of the casting and the position of the area to be repaired on the casting.

[0021] Through the above-mentioned method, the repair path of the laser beam can be better adapted to the area to be repaired, and the repair accuracy can be higher.

[0022] In this specification, when the area to be repaired is melted by a laser beam, the following steps are also included:

[0023] Determine whether the filling material deviates from the defective position on the casting surface, or the laser beam deviates from the area to be repaired, or the casting in the area to be repaired cannot be repaired;

[0024] If present, stop melting the area to be repaired.

[0025] In this specification, before rubbing the repair area with the rubbing head, the following steps are also included:

[0026] Determine the size of the repair area;

[0027] The inclination angle of the friction head is determined according to the size of the area to be repaired, the shape of the casting and the position of the repair area on the casting.

[0028] Specifically, it is possible to determine whether the repair area is a plane or a curved surface based on the shape of the casting and the position of the repair area on the casting. If it is a curved surface, the inclination angle of the friction head can be adjusted accordingly so that the friction surface of the friction head can be parallel to the surface where the repair area is located, thereby avoiding problems during the repair process.

[0029] In this specification, the friction head performs secondary repair on the repair area, including the following steps:

[0030] The friction head extrude the repaired softened layer during the moving process;

[0031] During the friction and extrusion process, the friction head fills the extruded filling material into the cavity formed in the repair area behind the friction head.

[0032] Specifically, the workpiece used for friction and secondary repair has a cylindrical shoulder (i.e., a friction head), one side of which (i.e., the bottom surface of the cylinder) abuts against the repair area and has an extrusion effect on the repair area. Moreover, the bottom surface of the friction head should be uniform, that is, it can make the pressure of the bottom surface on each position of the repair area uniform. In addition, when performing secondary repair, after the friction head abuts against the surface of the repair area, it can move along the repair area or the surface of the casting in a preset direction. During the movement, the friction head can evenly remove the residual stress of the filling material and the defective position of the repair area. At the same time, the extrusion effect of the friction head on the repaired softened layer can make the extruded material fill the cavity formed by the rotation of the friction head, so that the repaired casting has no defects and its residual stress can be removed.

[0033] It should be noted here that during the secondary repair, the friction head not only rubs the repair area in the moving direction, but also rotates itself and rubs the repair area in the rotation direction, so as to achieve the effect of removing residual stress.

[0034] Based on the above, it can be seen that the above repair process first uses the laser beam energy to melt the defective surface of the casting, which can reduce the damage of the repair to the casting as a whole. It is highly targeted and has a higher repair position accuracy. The repair area is then rubbed by the friction head to form a repair softening layer. When the friction head performs extrusion repair on the repair softening layer along the travel direction, the residual stress in the repair area can be effectively removed, and the stress deformation caused by the filling material repair in the repair area can be greatly reduced. Therefore, the above repair process can solve the problems of coarse grains, large residual stress, severe deformation and wide heat-affected zone after repair by the existing process.

[0035] In this specification, the laser beam is emitted by a laser, and the energy density of the laser beam is 1000W-1500W. Specifically, the energy density of the laser beam can more accurately reduce the width of the heat-affected zone, thereby avoiding the repair process from affecting other non-defective positions of the casting.

[0036] In this specification, the surface of the repair area and the surface of the casting are located in the same plane, so that the surface of the repaired casting is in a flat state and the repair effect is better.

[0037] In this specification, after the repair area solidifies and before the repair area is rubbed with the friction head, it also includes: stress detection of the repair area, and determining the extrusion force of the friction head on the repair area according to the detected stress. In detail, the above method can avoid setting the extrusion force too small or too large, so that the friction head damages the repair area, avoids the formation of new defects, and has a better repair effect and a faster repair process.

[0038] In this specification, when forming the repair softened layer and performing secondary repair, the friction head is pressed into the surface of the repair area to a depth of 0.05m-0.15m.

[0039] In this specification, when forming the repaired softened layer and performing secondary repair, the travel speed of the friction head is 30 mm / min-70 mm / min, and the rotation speed of the friction head is 200 r / min-400 r / min.

[0040] In this specification, the setting range of the pressing depth of the friction head, the travel speed of the friction head and the rotation speed of the friction head can ensure the repair effect of the repair area, avoiding the problem of insufficient repair force resulting in poor repair effect or excessive repair force resulting in new defects during repair.

[0041] In this specification, a side of the friction head used for friction is provided with a plurality of short needles, and before the friction head is used to rub the repair area, the method further includes: inserting the short needles into the surface of the solidified repair area.

[0042] In this specification, a plurality of short needles may be provided on one side of the friction head or no short needles may be provided. When short needles are provided, during the rotation of the friction head, the short needles have a stirring effect on the surface of the repair area, which can further remove the residual stress in the repair area.

[0043] It should be noted that the friction head squeezes the repaired softened layer during the movement;

[0044] During the friction and extrusion process, micropores will be formed due to the setting of the short needles. During the movement of the friction head, the extruded filling material can be filled into the micropores behind the movement to avoid the emergence of new defects. At the same time, the residual stress in the repair area can be further removed.

[0045] In this specification, the diameter of the short needle is 45mm-55mm, and the length of the short needle is 0.5mm-1.0mm. The above-mentioned arrangement of the short needle can avoid the problem that the new defects cannot be filled due to the short needle diameter being too large, and can also avoid the problem that the stirring effect is poor due to the short needle diameter being too small, and the length of the short needle can prevent the short needle from penetrating too deep into the casting surface, thereby avoiding deep defects that cannot be repaired.

[0046] In this manual, before the above repair process is carried out, the repair and assembly of the workpiece should be carried out in accordance with the requirements of the technical documents or process specifications, and the repair and assembly process should avoid secondary contamination. During the installation process, the clamp (tool for clamping the casting) should be evenly and symmetrically applied to avoid warping, bending and deformation of the workpiece.

[0047] The embodiments of this specification have at least the following advantages or beneficial effects:

[0048] Compared with the existing technology, the above-mentioned repair process first melts the defective surface of the casting through the energy of the laser beam, which can reduce the damage of the repair to the casting as a whole. It is highly targeted and has a higher accuracy of the repair position. The repair area is then rubbed by the friction head to form a repair softening layer. When the friction head performs extrusion repair on the repair softening layer along the moving direction, the residual stress in the repair area can be effectively removed, and the stress deformation in the repair area caused by the filling material repair is greatly reduced. Therefore, the above-mentioned repair process can solve the problems of coarse grains, large residual stress, severe deformation and wide heat-affected zone after repair by the existing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of this specification, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present specification and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying any creative work.

[0050] Figure 1 Schematic diagram of the principle of repairing casting surface defects by laser beam provided in this manual;

[0051] Figure 2 Schematic diagram of the repair principle for removing residual stress provided in this manual. DETAILED DESCRIPTION

[0052] To make the purpose, technical scheme and advantages of the embodiments of this specification clearer, the technical scheme in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are part of the embodiments of this specification, rather than all the embodiments. If the specific conditions are not indicated in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not indicated in the reagents or instruments used, conventional products that can be obtained by commercial purchase can be obtained.

[0053] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other. The present invention will be described in detail below with reference to specific embodiments.

[0054] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0055] Example 1

[0056] Please refer to Figure 1 to Figure 2 ( Figure 1 The parent material shown in is the casting. Figure 2 The workpiece to be welded shown in the figure is a casting), and the purpose of this embodiment is to provide a low-stress composite repair process for magnesium alloy casting defects, which mainly includes:

[0057] Filling a filling material into a defective position on the surface of the casting to obtain an area to be repaired, wherein the filling material may be a magnesium alloy, and the casting material is a magnesium alloy;

[0058] The repair area is melted by a laser beam to form the repair area;

[0059] After the repair area solidifies, the repair area is rubbed with a friction head (without a short needle) to form a repair softened layer. At the same time, the friction head performs secondary repair on the repair area to obtain a repaired casting.

[0060] In this embodiment, the process parameter setting for repairing the filling area with a laser beam can specifically refer to the following three situations:

[0061] Table 1 Process parameters of laser repair of Example 1

[0062]

[0063] In this embodiment, the process parameter setting of the secondary repair can specifically refer to the following five situations:

[0064] Table 2 Process parameters of secondary repair of Example 1

[0065]

[0066]

[0067] Example 2

[0068] Please refer to Figure 1 to Figure 2 The purpose of this embodiment is to provide a low-stress composite repair process for magnesium alloy casting defects, which mainly includes:

[0069] Filling a filling material into a defective position on the surface of the casting to obtain an area to be repaired, wherein the filling material may be a magnesium alloy, and the casting material is a magnesium alloy;

[0070] The repair area is melted by a laser beam to form the repair area;

[0071] After the repair area solidifies, the repair area is rubbed with a friction head (provided with a short needle with a diameter of 45mm-55mm and a length of 0.5mm-1mm, and the short needle is inserted into the surface of the repair area) to form a repair softening layer. At the same time, the friction head performs secondary repair on the repair area to obtain a repaired casting.

[0072] In this embodiment, the process parameter setting for repairing the filling area with a laser beam can specifically refer to the following three situations:

[0073] Table 3 Process parameters of laser repair of Example 2

[0074] Serial number Laser power(W) Filling speed of filling material (m / min) Repair speed (m / min) 1 1000 2.5 0.4 2 1200 3.0 0.8 3 1500 2.5 0.8

[0075] In this embodiment, the process parameter setting of the secondary repair can specifically refer to the following five situations:

[0076] Table 4 Process parameters of secondary repair of Example 2

[0077] Serial number Rotation speed of friction head (r / min) Repair speed (mm / min) Pressing depth (m) 1 200 30 0.05 2 200 50 0.10 3 300 50 0.05 4 300 70 0.10 5 400 70 0.15

[0078] Example 3

[0079] Please refer to Figure 1 to Figure 2 The purpose of this embodiment is to provide a low-stress composite repair process for magnesium alloy casting defects, which mainly includes:

[0080] 1. Clamping

[0081] Before repair, the repair and assembly of the casting should be carried out in accordance with the requirements of the technical documents or process specifications, and the repair and assembly process should avoid secondary contamination. During the installation process, the clamps used for the casting should be evenly and symmetrically applied to avoid warping, bending and deformation of the workpiece.

[0082] 2. Repair protection: During the entire repair process, inert gases such as Ar and He should be used to protect the front of the repair area. The gas protection range should cover the molten pool and the surrounding area with a temperature higher than 250°C. During the repair process, the nozzle method can be used to protect the repair molten pool and the surrounding high-temperature area. When the nozzle method is used for protection during the repair process, gas should be supplied in advance and then stopped. The pre-gas supply time before repair is greater than 3s, and the delayed gas supply after repair is not less than 5s. 3. Pretreatment before repair

[0083] For castings with internal defects, the internal defects should be excavated before repair. Before repair, the oxide film, oil stains and foreign matter on the inner and outer surfaces of the defect repair area of ​​the casting should be cleaned. After cleaning, the repair should generally be carried out within 24 hours; if it exceeds 24 hours, the oxide film in the repair area should be cleaned first, and then cleaned with alcohol or acetone, and the repair can be continued after drying.

[0084] 4. Laser repair

[0085] Before laser repair, the repair path and repair time of the laser beam are determined according to the size of the defect repair area of ​​the casting, and the deflection angle of the laser repair head and the spatial position of the filling material filling mechanism are fully considered.

[0086] After the laser repair path is determined, the repair path and repair time cannot be changed at will. If one of the following situations occurs during the laser repair process, the repair should be stopped: first, the filling material deviates from the defect position; second, serious quality problems occur in the repair area; third, the laser beam deviates from the preset path track.

[0087] For point defects on the surface of castings, such as small pinhole defects, when using laser, the laser emits a high-energy density laser beam, which is focused on the surface of the area to be repaired in the casting and melted under the action of internal optical components and optical systems, and then quickly cooled and solidified; for internal volume defects, such as larger pores, cold shuts and other defects, the laser beam emitted by the laser is used to melt the surface of the area to be repaired in the casting and the filling material at the same time, and then the molten filling material solidifies and crystallizes to form a repair area on the surface of the casting.

[0088] 5. Secondary repair: friction stir residual stress homogenization treatment

[0089] According to the size of the repair area and the position of the repair area in the casting, it is determined whether the repair area is located on a curved surface or a flat surface. According to the curve or surface where the repair area is located, the repair path and inclination angle of the friction head are determined so that the shoulder of the friction head and the surface where the repair area is located are parallel during repair.

[0090] After laser repair, the repair area surface is subjected to stress relief treatment by stir friction. A friction head without needle or short needle (0.5-1mm) is used to perform stress homogenization treatment on the laser repair area by stir friction; and during the repair process, the amount of downward pressure can be fine-tuned in real time according to the change in the height of the casting surface to ensure the stress relief effect of the repair area.

[0091] Principle of secondary repair: After laser repair, a large amount of residual stress is generated inside the repair area, and friction stirring is used to homogenize and relieve stress. The high-speed rotating friction head (with short needles) pierces the repair area of ​​the casting and moves in the repair direction. Friction heat is generated at the contact point between the friction head and the casting surface, so that the nearby metal forms a plastic softening layer (that is, the repair softening layer). The softened layer fills the cavity formed behind the short needle under the action of the rotation of the friction head, and the residual stress of the material is homogenized under the stirring and extrusion of the shaft shoulder and the short needle.

[0092] Comparative Example 1

[0093] The defects are repaired by the laser repair proposed in Example 2, and the laser repair parameters are as follows:

[0094] Table 5 Parameter settings of laser repair of comparative example 1

[0095] Laser power(W) Filling speed of filling material (m / min) Repair speed (m / min) 1200 3.0 0.8

[0096] The difference from Example 2 is that no secondary repair is performed.

[0097] Effect example

[0098] 1. Tensile performance test of repaired castings

[0099] The repaired casting proposed in Example 2 was used as a test sample (the repair parameters are shown in Table 6), and the tensile strength of the samples before and after the repair was tested. The samples are divided into: Sample 1: a casting after the point defects on the surface of the original casting were repaired by the repair process proposed in Example 2 (the repair parameters are shown in Table 6); Sample 2: a casting after the volume defects inside the original casting were repaired by the repair process proposed in Example 2 (the repair parameters are shown in Table 6); the specific effects are shown in the following table:

[0100] Table 6 Repair parameters of test samples

[0101] Laser beam power (W) Filling speed of filling material (m / min) Repair speed (m / min) 1200 3.0 0.8 Rotation speed of friction head (r / min) Repair speed (mm / min) Pressing depth (m) 300 50 0.05

[0102] Table 7 Mechanical properties test results of test samples

[0103] sample Tensile strength / MPa Yield limit / MPa Elongation / % Original casting before restoration 171 91 4.8 Sample 1 165 104 3.5 Sample 2 157 115 3.2

[0104] 2. Residual stress test of repaired castings

[0105] An ultrasonic stress meter was used to take points on both sides of the repaired area for measurement. Two points were selected in each of the five repaired areas, one point was located on the side after the secondary repair, and the other point was located on the side of the laser repair area that had not undergone secondary repair. Specifically, the repair process proposed in Example 2 (i.e., composite repair, repair parameters are shown in Table 6) was used to repair some point defects in five areas on the surface of the original casting, and the repair process proposed in Comparative Example 1 (laser repair) was used to repair some point defects in five areas on the surface of the original casting. The test results are shown in Table 8.

[0106] Table 8 Residual stress test results

[0107]

[0108] Comparison shows that compared with single laser repair, composite repair can greatly reduce the residual stress in the repaired area of ​​the casting, and the casting after secondary repair has the advantages of small deformation and high dimensional accuracy.

[0109] The embodiments described above are part of the embodiments of the present invention, rather than all of the embodiments. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A low stress composite repair process for magnesium alloy casting defects, characterized in that: The following steps are involved: Filling the defective position on the surface of the casting with a filling material to form an area to be repaired, wherein the filling material is consistent with the material of the casting; The repair area is melted by a laser beam to form the repair area; After the repair area solidifies, the repair area is rubbed with a friction head to form a repair softened layer. At the same time, the friction head performs secondary repair on the repair area to obtain a repaired casting.

2. The low stress composite repair process for magnesium alloy casting defects according to claim 1, characterized in that: During the whole repair process, inert gas is used to protect the area to be repaired, the repair area and the repaired softened layer, and the inert gas at least covers the area with a temperature higher than 250°C.

3. The low stress composite repair process for magnesium alloy casting defects according to claim 1, characterized in that: After the repair area solidifies and before the repair area is rubbed with the friction head, the method further includes: performing stress detection on the repair area, and determining the extrusion force of the friction head on the repair area / the extrusion force of the repair softened layer according to the detected stress.

4. The low stress composite repair process for magnesium alloy casting defects according to claim 1, characterized in that: The friction head performs secondary repair on the repair area, comprising the following steps: The friction head extrude the repaired softened layer during the moving process; The friction head fills the extruded filling material into the cavity formed in the repair area behind the friction head.

5. The low stress composite repair process for magnesium alloy casting defects according to claim 1, characterized in that: Before the area to be repaired is melted with a laser beam, the following steps are also included: Determine the size of the area to be repaired; The repair path of the laser beam on the area to be repaired is determined according to the size of the area to be repaired, the shape of the casting and the position of the area to be repaired on the casting.

6. The low stress composite repair process for magnesium alloy casting defects according to claim 1 or 5, characterized in that: When melting the area to be repaired with a laser beam, the following steps are also included: Determine whether the filling material deviates from the defective position on the casting surface, or the laser beam deviates from the area to be repaired, or the casting in the area to be repaired cannot be repaired; If present, stop melting the area to be repaired.

7. The low stress composite repair process for magnesium alloy casting defects according to claim 1, characterized in that: Before rubbing the repair area with the rubbing head, the following steps are also included: Determine the size of the repair area; According to the size of the repair area, the shape of the casting and the position of the repair area on the casting, determine whether the surface where the repair area is located is a curved surface or a flat surface; The inclination angle of the friction head and the repair path of the friction head are determined according to the shape of the surface where the repair area is located.

8. The low stress composite repair process for magnesium alloy casting defects according to claim 1, characterized in that: During friction and secondary repair, the friction head is pressed into the surface of the repair area to a depth of 0.05m-0.15m, the travel speed of the friction head is 30mm / min-70mm / min, the rotation speed of the friction head is 200r / min-400r / min, and the energy density of the laser beam is 1000w-1500w.

9. The low stress composite repair process for magnesium alloy casting defects according to claim 1, characterized in that: A plurality of short needles are arranged on one side of the friction head for friction. Before the repair area is rubbed with the friction head, the method further comprises: inserting the short needles into the surface of the solidified repair area.

10. The low stress composite repair process for magnesium alloy casting defects according to claim 9, characterized in that: The diameter of the short needle is 45mm-55mm, and the length of the short needle is 0.5mm-1.0mm.

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