光斑搭接率对激光清洗铝合金阳极氧化膜表面质量及耐磨性能的影响

Effect of Spot Overlap Rate on Surface Quality and Wear Resistance of Laser Cleaned Aluminum Alloy Anodic Oxide Film

目的研究激光清洗铝合金表面阳极氧化膜后,光斑搭接率对基材表面质量及磨损性能的影响规律。方法采用纳秒脉冲激光器清洗7075铝合金表面的阳极氧化膜,分析不同激光光斑搭接率(20%~60%)对材料表面形貌、元素含量、表面粗糙度、显微硬度、残余应力和耐磨性的影响,通过研究激光清洗后7075铝合金的表面特征,探究激光光斑搭接率对铝合金表面耐磨性的影响规律。结果随着光斑搭接率的减小,被清洗表面的显微硬度、粗糙度均呈现先减少后增大的趋势,残余应力呈现下降趋势。当光斑搭接率为46.7%~60%时,试样表面存在烧蚀形成的凹坑,导致粗糙度增大。当光斑搭接率为20%时,氧元素的含量较高,氧化膜去除不完整,达不到清洗要求。当激光光斑搭接率为33.3%时,激光清洗能够有效去除7075铝合金表面的阳极氧化膜,并会形成粗糙度较小、显微硬度较大的熔融热氧化层。结论经不同光斑搭接率清洗后,清洗表面磨损机制主要以磨粒磨损和剥层磨损为主,在光斑搭接率为33.3%时,表面清洗效果较好,同时清洗后的表面生成的熔融热氧化层可以提高耐磨性,此时样件表面磨损量达到最低值,这为铝合金清洗后重新使用提供了可行性。

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 2500 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 0.252μm,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 0.194μm.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.