Effect of Spot Overlap Rate on Surface Quality and Wear Resistance of Laser Cleaned Aluminum Alloy Anodic Oxide Film
The purpose of laser cleaning to remove the oxide film is to completely remove the anodic oxide film on the surface of the 7075 aluminum alloy substrate without damaging it.The wear resistance of the 7075 aluminum alloy substrate surface after laser cleaning is guaranteed to be no weaker than that of the original substrate,meeting the actual use of the material.Therefore,the influence of spot overlap rate on the surface quality and wear performance of the substrate after laser cleaning of the anodized film on the surface of aluminum alloy is studied.A nanosecond pulse laser with a laser power of 2 500 W,a frequency of 2.5 kHz,a laser spot overlap rate of 20%-60%,and a spot diameter of 1.5 mm was used to clean the anodic oxide film on the surface of 7075 aluminum alloy in this article.Hitachi S-3400N scanning electron microscope,Olympus DSX1000 ultra depth of field microscope,SIDA HVS-1000A,Proto iXRD Combo residual stress tester,and Lianyungang MMW-1A universal friction and wear tester were used to analyze the effects of different laser spot overlap rates on the surface morphology,element content,surface roughness,microhardness,residual stress,and wear resistance of materials.According to the research results on the surface characteristics of 7075 aluminum alloy after laser cleaning,the influence of laser spot overlap rate on the wear resistance of aluminum alloy surface was explored.The results showed that as the overlap rate of spots decreased,the microhardness and roughness of the cleaned surface first decreased and then increased,and the residual stress decreased.When the overlap rate of the light spot was 46.7%-60%,pits formed by ablation appeared on the surface of the sample,causing an increase in roughness.When the overlap rate of spots was 20%,the oxygen content was high(6.44%),the surface anodic oxide film was not completely removed,and the surface roughness was 0.252 μm,which was unable to meet cleaning requirements.When the laser spot overlap rate was 33.3%,the surface oxygen content of 7075 aluminum alloy was 0.43%,the sulfur content was 0.1%,and the surface roughness was 0.194 μm.Laser cleaning could effectively remove the anodic oxide film on the surface of 7075 aluminum alloy,and there was no significant damage to the surface of the aluminum alloy substrate after laser cleaning.After cleaning,under laser shock wave and recoil pressure,slight dislocation deformation occurred on the surface of the substrate,making it difficult for grains to shift and slide,and increasing hardness.At the same time,a molten thermal oxide layer with low roughness and high microhardness formed on the surface.After cleaning with different spot overlap rates,the wear mechanism of the cleaned surface is mainly abrasive wear and peeling wear.When the overlap rate of spots is 33.3%,the surface cleaning effect is better,and the molten thermal oxide layer generated by cleaning the surface can improve the wear resistance.At this point,the sample can reach a stable friction state faster than other parameters after friction.Furthermore,the friction coefficient and the wear amount on the surface of the sample are the lowest,and the wear resistance is the best,providing feasibility for the reuse of aluminum alloy after cleaning.
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