A high-strength aluminum alloy laser additive repair method based on multi-dimensional stress regulation

Abstract

A high-strength aluminum alloy laser additive repair method based on multi-dimensional stress regulation relates to the field of laser additive repair technology. By laser prestressing the bottom and surface of the repair area, a compressive stress layer of a certain thickness is formed at the bottom of the repair area. The pre-set compressive stress layer and the tensile stress generated by the deposited layer after the repair are offset, reducing the residual stress level and the deformation of the repaired part. After the compressive stress layer is pre-set on the surface of the repair area, the surface strengthening effect generated improves the fatigue performance of the part during service and extends its reliability service cycle. This method can reduce pores, eliminate cracks, and increase the fatigue life of the repair area. Without changing the original dynamic characteristics and usage function of the high-strength aluminum alloy structure, it performs in-situ additive repair on the surface defective areas, thereby extending its service life, reducing the maintenance cost of high-value-added parts, and increasing the service fatigue life of the repair area.

Description

Technical Field

[0001] The present invention relates to the technical field of laser additive repair, and in particular to a high-strength aluminum alloy laser additive repair method based on multi-dimensional stress regulation. Background Art

[0002] 7075 aluminum alloy, a highly representative ultra-hard, high-strength aluminum alloy, boasts advantages such as low density, high specific strength, high specific stiffness, ease of processing, and excellent corrosion resistance. High-performance aerospace components often serve in extremely harsh environments, requiring materials with exceptional load-bearing properties, extreme heat resistance, ultra-lightness, and high reliability. Consequently, 7075 aluminum alloy has been used in the aircraft manufacturing industry since the 1940s, becoming one of the industry's primary structural materials, primarily in critical components such as aircraft struts, wings, fins, and main load-bearing frame beams.

[0003] However, in actual applications, with the development of aerospace technology, the speed and carrying capacity of aircraft have been continuously improved. During their service, they are often subjected to the interaction of complex loads and harsh environments, and are susceptible to fatigue, corrosion fatigue, stress corrosion and other effects. This places high demands on the comprehensive performance of high-strength aluminum alloys. In addition, their preparation process is usually traditional casting process and manual polishing, which is inefficient, the surface quality is uneven, and it is also prone to phenomena such as missing meat, misprocessing, and out-of-tolerance. The above defects will make parts more prone to fatigue wear and cracks during service, causing reliability and durability problems, leading to premature failure and scrapping of parts, thereby reducing the attendance efficiency of aviation equipment, and also increasing the possibility of accidents, seriously threatening the safety of pilots and aviation equipment. Therefore, high-performance repair work of high-value-added parts is of particular importance in the aviation field.

[0004] However, currently, most effective high-strength aluminum alloy repair processes use traditional welding methods. This high heat input results in large deformations in the heat-affected zone (HAZ) and parts, and a high number of cracks and defects in the repaired area. This makes it difficult to achieve high-quality and high-precision repairs of thin-walled, complex-shaped parts. Surface defects such as undercuts, pores, and cracks are also easily formed. The large HAZ makes stress concentration more likely in the repaired area, severely degrading the uniformity of the overall mechanical properties of the part. This results in the current situation where damaged high-strength aluminum alloy parts, especially forged ones, need to be discarded on aircraft. This treatment method significantly wastes materials and increases aircraft maintenance costs. Furthermore, the reliability of the new parts needs further verification, significantly extending the aircraft's maintenance cycle.

[0005] Laser additive repair technology uses high-energy lasers to perform in-situ repairs on damaged parts of the structure. At the same time, laser shock peening is used to pre-stress the bottom of the defect and the surface of the repair layer before and after the damaged part is repaired. Its functions are as follows: 1) A compressive stress layer is generated at the bottom of the defect to be repaired, which offsets the tensile stress generated by the solidification shrinkage of the repair area, thereby inhibiting the generation of crack defects in the repair area; 2) Laser shock peening is performed on the surface of the completed repair area to form a favorable compressive stress layer on the surface of the repair area, which can significantly improve the fatigue life and overall performance of the repair layer.

[0006] However, 7-series aluminum alloys, including 7075 aluminum alloy, suffer from poor melt fluidity, high laser reflectivity, high thermal conductivity, and strong oxidizing properties. This results in high porosity and a severe cracking tendency in the deposited area during laser additive repair. Furthermore, the presence of a heat-affected zone (HAZ) is still unavoidable during additive repair. These issues ultimately impact the performance of the repaired part. Summary of the Invention

[0007] To address the technical challenges of aluminum alloy laser repair, such as the generation of internal defects such as pores, lack of fusion, and cracks during material formation, as well as excessive internal residual stress leading to part deformation, the present invention provides a high-strength aluminum alloy laser additive repair method based on multi-dimensional stress control. This method can reduce pores, eliminate cracks, and increase the fatigue life of the repaired area. Without changing the original dynamic characteristics and usability of the high-strength aluminum alloy structure, it performs in-situ additive repair on the surface defective areas, thereby extending their service life, reducing the maintenance cost of high-value-added parts, and increasing the service fatigue life of the repaired area.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A high-strength aluminum alloy laser additive repair method based on multi-dimensional stress regulation includes the following steps:

[0010] Step 1: Clean the surface of the damaged high-strength aluminum alloy part; remove the damaged area by milling, and create a V-groove suitable for additive repair on the damaged area of the part;

[0011] Step 2: Grind the milled area to be repaired to remove the surface oxide layer, and use a solvent to wipe and decontaminate the area to be repaired; scan the damaged part after milling with a 3D scanner to obtain a 3D repair model of the damaged part, and compare the model with the original part model;

[0012] Step 3: Use additive manufacturing layered slicing and path planning software to perform trajectory planning on the 3D model of the additive area to obtain the optimal scanning path for the laser during additive repair;

[0013] Step 4: vacuum drying the high-strength aluminum alloy powder and particle reinforcement powder for repair;

[0014] Step 5: Place the dried high-strength aluminum alloy powder and particle reinforcement powder in the powder feeding buckets of the multi-channel powder feeder, and set the powder feeding speed and carrier gas flow rate of the powder feeding buckets;

[0015] Step 6: Fix the parts on the ultrasonic vibration platform;

[0016] Step 7: Place the ultrasonic vibration platform into the electromagnetic field device, then seal it to form a sealed chamber and fill it with argon gas to prevent the influence of oxide doping on the quality of the repair area;

[0017] Step 8: Before the repair test begins, the groove area to be repaired is subjected to laser shock peening treatment to generate a compressive stress layer of a certain thickness at the bottom of the V-groove;

[0018] Step 9: After starting the ultrasonic vibration platform and electromagnetic field device, the multi-channel powder feeder and laser are turned on to deposit and print powder on the area to be repaired to construct the defect area; after the repair is completed, the surface of the repair area is first laser remelted to cause the porosity defects of the previous deposition layer to float up;

[0019] Step 10: After the repaired area is polished and smoothed, a secondary laser shock peening treatment is performed to form a compressive stress layer on the surface of the repaired area to improve its fatigue life and repair quality.

[0020] Furthermore, the damaged high-strength aluminum alloy part in step 1 is made of high-strength forged aluminum alloy or cast aluminum alloy.

[0021] Furthermore, the powder of step 4 needs to be dried in a vacuum environment at 150°C to 200°C for 3 to 8 hours; in order to improve the comprehensive mechanical properties of the repair area, the reinforcing phase particles are selected from TiC, TiB2, B4C and SiC, and the added mass fraction is 10wt.% to 35wt.%.

[0022] Furthermore, the ultrasonic vibration power of the ultrasonic vibration platform in step 6 is 100-400 W, the frequency is 15-25 kHz, and the ultrasonic amplitude is set to 10-50 μm.

[0023] Furthermore, the magnetic field strength of the electromagnetic field device in step 7 is 100-500 mT.

[0024] Furthermore, the laser powder feeding method for repairing the damaged portion in step 9 uses coaxial dual-path powder feeding, with a laser power of 1500-4000W, a scan rate of 300-800mm / min, a defocus of -4-4cm, a deflection angle of 5°-8°, a carrier gas flow rate of 3-8L / min, an overlap ratio of 40%-60%, an interlayer cooling time of 180-480s, and a lift of 0.3-1mm per layer. During laser remelting, no powder feeding or lift is performed, and the laser power is reduced by 100-500W.

[0025] Furthermore, in the laser shock peening process described in steps 8 and 10, the laser energy is 3 to 10 J, the pulse width is 12 to 16 ns, the repetition frequency is 0.5 to 3 Hz, and the spot diameter is 2 to 4 mm.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. A coaxial dual-path powder feeding solution eliminates uneven mixing of the aluminum powder and reinforcement powder used for repair in the powder mixer, as well as powder stratification during storage. Instead, the powder is uniformly conveyed and mixed during the repair process. This ensures a more uniform phase formation within the repaired part, further ensuring the dimensional accuracy and mechanical properties of the repaired area, such as wear and corrosion resistance.

[0028] 2. First, the addition of a DC electromagnetic field stabilizes the melt pool during the additive process, suppressing the violent flow of the melt during the laser scanning process. This also reduces crack defects and pores, and refines the grain size. Second, the combined effects of ultrasonic vibration and laser remelting further refine the grain size and accelerate the rise of bubbles in the melt during the additive process.

[0029] 3. By performing laser prestressing treatment on the bottom and surface of the repair area respectively, a compressive stress layer of a certain thickness is formed at the bottom of the repair area, so that the preset compressive stress layer and the tensile stress generated by the deposited layer after repair offset each other, reducing the residual stress level and the deformation of the repaired parts; after the compressive stress layer is preset on the surface of the repair area, the surface strengthening effect generated improves the fatigue performance of the parts during service and extends their reliability service cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of ultrasonic-electromagnetic coupled multi-physics field-assisted laser additive repair of 7075 alloy in an embodiment of the present invention; in the figure: 1 - magnetic induction coil; 2 - 7075 substrate with V-grooved milling process; 3 - ultrasonic vibrator.

[0031] Figure 2This is a schematic diagram of the multi-dimensional stress regulation before and after the repair of the repair area by introducing laser shock peening in an embodiment of the present invention; in the figure: 1-preset compressive stress layer before repair to offset the tensile stress generated during the repair process; 2-compressive stress layer generated by laser shock peening on the upper surface after the repair is completed and polished, to improve the fatigue life and reliability of the repair area.

[0032] Figure 3 Schematic diagram of the laser shock peening spot overlapping strategy of the present invention.

[0033] Figure 4 This is the effect of laser shock peening on the hardness and residual stress of the repaired area in Example 1 of the present invention.

[0034] Figure 5 This is the effect of the electromagnetic-ultrasonic composite field on the pore defects in the repair area in Example 1 of the present invention; the upper figure shows the traditional repair effect, and the lower figure shows the modification effect of the electromagnetic-ultrasonic composite field.

[0035] Figure 6 This is the effect of the technical solution of Example 1 of the present invention on improving the tensile strength of the repaired area.

[0036] Figure 7 This is the effect of the technical solution of Example 2 of the present invention on the maximum wear scar depth in the repaired area. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] The schematic diagram of the ultrasonic-electromagnetic coupling multi-physics field assisted laser additive repair of 7075 alloy in the embodiment of the present invention is as follows Figure 1 As shown in the figure, the schematic diagram of multi-dimensional stress control before and after repair of the repair area by introducing laser shock peening is shown in the figure. Figure 2 As shown, the schematic diagram of the laser shock peening spot overlapping strategy of the present invention is as follows Figure 3 shown.

[0040] A laser additive repair method for high-strength aluminum alloy based on multi-dimensional stress regulation, the specific operation steps are as follows:

[0041] The experimental substrate for the laser additive repair of high-strength aluminum alloys involved in the embodiments of the present invention is a 7075 aluminum alloy substrate with dimensions of 50 mm × 50 mm × 4 mm. The laser melting deposition system used in the experiment consists of a six-axis KR60-HA robot produced by KUKA, a YSL-10000-KC laser produced by IPG (maximum output power of 10 kW), an RC / PGF / D dual-barrel powder feeder produced by Zhongke Yuchen, a flexible sealed cabin, and an air-shielded internal powder feeding nozzle.

[0042] Step 1: Use milling to process a V-groove on the 7075 substrate.

[0043] Step 2: Polish the area to be repaired to remove the surface oxide layer, wipe and decontaminate the area to be repaired with anhydrous ethanol, scan the milled substrate with a 3D scanner, and obtain a 3D model of the repaired area of the substrate after milling through model inversion, and compare and analyze it with the original model of the part.

[0044] Step 3: Use additive manufacturing layered slicing and path planning software (3dAMPPPlanner software is selected) to perform trajectory planning on the V-groove three-dimensional model to obtain the optimal trajectory planning path for additive repair.

[0045] Step 4: Place the 7075 aluminum alloy powder and particle reinforcement powder for repair in a drying oven and dry them in a vacuum environment at 180°C for 5 hours. The reinforcement phase particles are selected as TiB2 with a particle size range of 53 to 150 μm and an added mass fraction of 20 wt.%.

[0046] Step 5: Place the dried 7075 aluminum alloy powder and the particle-enhanced powder into the left and right barrels of the double-barrel powder feeder, respectively, and set the powder feeding speed of the two barrels. The powder feeding speed of the 7075 aluminum alloy powder barrel is set to 1.0r / min, and the powder feeding speed of the particle-enhanced powder barrel is set to 0.5r / min. The carrier gas flow rate is set to 4.7L / min. It should be noted that the powder feeding speed is one of the key parameters in the technical solution of the present invention. Because the density of 7075 aluminum alloy and the enhanced particles is different, the mass fraction delivered per unit time and unit speed is also different. By measuring the weight of the powder delivered per unit time, the mass fraction of the added reinforcing phase is determined. Therefore, the mass fraction of each reinforcing phase corresponds to a fixed speed.

[0047] Step 6: Use 400-grit metallographic sandpaper to polish the milled V-grooves to remove the surface oxide layer, and then wipe off the oil and dirt on the substrate surface with 75% anhydrous ethanol. Finally, fix the dried substrate on an ultrasonic vibration platform with an ultrasonic vibration power of 200W and a frequency of 20kHz.

[0048] Step 7: Place the ultrasonic vibration platform into the electromagnetic field device, seal it, and set the magnetic field strength to 200 mT.

[0049] Step 8: Perform laser shock peening on the bottom surface of the V-groove to be repaired to form a preset compressive stress layer. The laser energy is 3J, the pulse width is 12ns, the repetition frequency is 0.5Hz, the spot diameter is 2mm, a 130μm thick black tape is used as the absorption protective layer, and deionized water with a thickness of about 1.2mm is selected as the constraint layer.

[0050] Step 9: Fill the sealed chamber with argon. Once the oxygen content drops below 100 ppm, laser additive repair begins according to the program settings, with powder being fed simultaneously from both the left and right powder feeders. The laser power is 2500 W, the deflection angle is 5°, the laser scanning speed is 10 mm / s, the spot diameter is 4 mm, the overlap ratio is 50%, the interlayer cooling time is 300 seconds, the defocus distance is 4 cm, and the laser power for laser remelting is 2000 W, with a scanning speed of 5 mm / s.

[0051] Step 10: After the additive repair is completed, the surface of the repaired area is polished until the surface is smooth. The surface of the polished repair layer is subjected to secondary laser shock peening treatment with a laser energy of 5J, a pulse width of 12ns, a repetition frequency of 0.5Hz, a spot diameter of 3mm, a 130μm thick black tape as the absorption protective layer, and deionized water with a thickness of about 1.2mm is selected as the constraint layer. Cross-sectional samples along the deposition direction after repair are cut by wire cutting and ground, polished, and corroded. The microstructural evolution of the repaired area, heat-affected zone, and matrix area is observed, and the differences in the organization and performance of the matrix material in the repaired area are comprehensively evaluated.

[0052] Laser shock peening can significantly improve the microhardness of the repaired area, from the average hardness of 91.45HV of the traditional repair method to 119.27HV after laser shock peening. After laser shock peening, the surface stress state of the repaired area changes from the maximum tensile stress of 115MPa in the traditional repair method to the maximum compressive stress of -153MPa. The change in stress state can significantly improve the fatigue performance of the repaired area and extend the service life of the reliability ( Figure 4 ).

[0053] like Figure 5 As shown in the figure, the repair process using the traditional repair scheme has many pore defects. By applying the technical solution of the present invention, the pore defects in the repaired area are significantly reduced, and the stress level at the interface is significantly reduced, thereby improving the comprehensive mechanical properties of the repaired area. Figure 6 As shown, the tensile strength of the repaired area is increased from 259.3 MPa of the traditional repair method to 325.7 MPa of the present invention, and the tensile strength of the repaired area reaches 95.8% of the parent material (the average tensile strength of the parent material is about 340 MPa).

[0054] Example 2

[0055] A laser additive repair method for high-strength aluminum alloys based on multi-dimensional stress control. Example 1 targets defects such as fatigue cracks generated during the service life of load-bearing forged aluminum alloy components, focusing on the tensile mechanical properties and the type and magnitude of residual stress in the repaired area. Example 2 targets defects caused by dimensional deviations due to friction and wear in the service life of cast aluminum alloy components, focusing on the wear resistance of the repaired area. The specific operating steps are the same as those in Example 1, except that:

[0056] (1) The aluminum alloy system to be repaired used in step 1 is a cast Al-Si alloy;

[0057] (2) The reinforcement phase particles used in step 4 are TiC and SiC. The TiC particles have a particle size range of 53-150 μm and a mass fraction of 10%; the SiC particles have a particle size range of 13-53 μm and a mass fraction of 20%.

[0058] (3) The ultrasonic vibration power of the ultrasonic vibration platform in step 6 is 400 W and the frequency is 25 kHz;

[0059] (4) The magnetic field strength in step 7 is set to 500 mT.

[0060] (5) In order to improve the wear resistance of the repaired area and retain the TiC and SiC particles to the maximum extent, the laser power in step 9 is set to 1500 W to prevent excessive melting of the ceramic particles, and the laser remelting process in step 9 of Example 1 is eliminated.

[0061] like Figure 7 As shown, the maximum wear scar depth of the traditional repair method is about 55 μm, and the maximum wear scar depth of the technical solution of the present invention is about 30 μm. The smaller the wear scar depth, the higher the hardness value of the material and the better the wear resistance.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-strength aluminum alloy laser additive repair method based on multi-dimensional stress control, characterized in that: The following steps are involved: Step 1: Clean the surface of the damaged high-strength aluminum alloy parts; Milling is used to remove the damaged parts and V-grooves for additive repair are machined on the damaged parts. Step 2: Grind the milled area to be repaired to remove the surface oxide layer, and use a solvent to wipe and decontaminate the area to be repaired; Scan the damaged parts after milling with a 3D scanner to obtain a 3D repair model of the damaged parts, and compare the model with the original part model; Step 3: Use additive manufacturing layered slicing and path planning software to perform trajectory planning on the 3D model of the area to be repaired, and obtain the optimal scanning path for the laser during additive repair. Step 4: vacuum drying the high-strength aluminum alloy powder and particle reinforcement powder for repair; Step 5: Place the dried high-strength aluminum alloy powder and particle reinforcement powder in the powder feeding barrels of the coaxial dual-path powder feeder, and set the powder feeding speed and carrier gas flow rate of the powder feeding barrels; Step 6: Fix the parts on an ultrasonic vibration platform; the ultrasonic vibration power of the ultrasonic vibration platform is 100-400W, the frequency is 15-25kHz, and the ultrasonic amplitude is set to 10-50μm; Step 7: Place the ultrasonic vibration platform into the electromagnetic field device, then seal it to form a sealed chamber and fill it with argon gas to prevent the influence of oxide doping on the quality of the repaired area; the magnetic field strength of the electromagnetic field device is 100-500mT; Step 8: Before the repair test begins, the V-groove area to be repaired is subjected to laser shock peening treatment to generate a compressive stress layer at the bottom of the V-groove. During the laser shock peening process, the laser energy is 3-10 J, the pulse width is 12-16 ns, the repetition frequency is 0.5-3 Hz, and the spot diameter is 2-4 mm. Step 9: After starting the ultrasonic vibration platform and electromagnetic field device, turn on the coaxial dual-path powder feeder and laser to deposit and print powder on the repair area to construct the damaged part; the laser power is 1500-4000W, the scanning rate is 300-800mm / min, the defocus is -4-4cm, the deflection angle is 5°-8°, the carrier gas flow rate is 3-8L / min, the overlap rate is 40%-60%, the interlayer cooling time is 180-480s, and the lift of each layer is 0.3-1mm; After the repair is completed, the surface of the repaired area is first laser remelted to cause the porosity defects of the previous deposition layer to float up. During laser remelting, no powder is fed and no lifting occurs. The laser power during laser remelting is 100 to 500W lower than that during repair. Step 10: After the repair area is polished and smooth, a secondary laser shock peening treatment is performed to form a compressive stress layer on the surface of the repair area to improve its fatigue life and repair quality. During the laser shock peening process, the laser energy is 3~10J, the pulse width is 12~16ns, the repetition frequency is 0.5~3Hz, and the spot diameter is 2~4mm.

2. The high-strength aluminum alloy laser additive repair method based on multi-dimensional stress control according to claim 1 is characterized in that: The damaged high-strength aluminum alloy part described in step 1 is made of high-strength forged aluminum alloy or cast aluminum alloy.

3. The high-strength aluminum alloy laser additive repair method based on multi-dimensional stress control according to claim 1 is characterized in that: The powder in step 4 is dried in a vacuum environment at 150°C to 200°C for 3 to 8 hours; the particle reinforcement powder is selected from TiC, TiB2, B4C and SiC, and the amount of the particle reinforcement powder added accounts for 10wt.% to 35wt.% of the total mass of the high-strength aluminum alloy powder and the particle reinforcement powder.

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