激光清洗具有绿色环保、劳动强度低、精确可控、灵活性好、非接触式清洗、易实现自动化等优点,在制造、维修与再制造领域的应用越来越广泛。激光清洗可发挥光压力、热烧蚀、振动波、等离子体冲击等多种效应的综合作用,实现基体表面优质高效清洁。激光在去除基体表面覆层的同时,覆层烧蚀和激光残余辐照作用会在基体表面产生热聚集和应力累积,不可避免地引起基体表面微观形貌、组织结构及性能的变化,并进一步影响基体的表面质量。采用纳秒激光对6061铝合金表面漆层进行清洗,分别采用高能量密度单次清洗和低能量密度二次清洗等2种方法,通过优化激光能量密度和光斑重叠率等工艺参数,研究激光清洗后铝合金表面形貌和性能的演变规律。结果表明,虽然单次清洗的效率较高,但易在铝合金表面形成氧化膜和非晶纳米改性层,显著提高了表面的耐蚀性和耐磨性;二次清洗在较低能量密度下能够更彻底地去除漆层,且对基体表面的损伤较小,表面粗糙度更低,保留了更多的原始成分。通过SEM、EDS、XPS、TEM等表征手段证实,二次清洗能够有效减少表面氧化,形成更均匀的表面形貌。电化学腐蚀测试结果表明,经单次清洗后,显著提升了铝合金表面形成的氧化膜的耐腐蚀性,其腐蚀电流密度最低达到2.221 3× 10-6 A/cm2;经二次清洗后,腐蚀电流密度为4.126 5×10-6 A/cm2,表明其耐腐蚀性有所提升。摩擦学性能测试结果显示,经二次清洗后,表面的摩擦因数较低,表明其耐磨性更好。本研究为铝合金表面激光清洗工艺的优化提供了理论依据,并展示了激光清洗从无损清洗到表面强化的潜力。
Abstract
Laser cleaning has the advantages of environmental protection, low labor intensity, accuracy and controllability, good flexibility, non-contact cleaning, easy automation, etc., and is widely used in the fields of manufacturing, maintenance and remanufacturing. Laser cleaning can play a comprehensive role of light pressure, thermal ablation, vibration wave, plasma impact and other effects to achieve high-quality and efficient cleaning of the substrate surface. However, when laser removes the coating on the surface of the substrate, the ablation of the coating and laser afterirradiation will produce heat accumulation and stress accumulation on the surface of the substrate, which will inevitably cause changes in the micro-morphology, microstructure and properties of the substrate surface, and further affect the surface quality of the substrate. In this study, the nanosecond pulsed laser was used to study the surface morphology and properties of 6061 aluminum alloy after laser cleaning of the paint layer, and two cleaning methods were used, including single high energy density cleaning and double low energy density cleaning. The cleaning process was optimized by changing laser power, scanning speed, line spacing and dot overlap rate. Single cleaning achieved higher efficiency, but caused more significant changes in the surface morphology. At higher energy density, it led to the formation of oxide film and amorphous nano-modified layer, which increased the change of surface roughness and microstructure. SEM and EDS analysis confirmed the existence of metal oxides and remelting areas on the surface, indicating the potential degradation of other performance characteristics. Remelting and oxidation led to rough porous structure, which affected the mechanical properties of the alloy. It was worth noting that the oxide layer provided a certain degree of corrosion resistance, which was suitable for applications requiring protective oxide layer and enhanced corrosion resistance. In contrast, double cleaning at lower energy density could bring less substrate damage. The lower energy prevented overheating and remelting, resulting in a smoother and cleaner surface. SEM and EDS analysis showed that the aluminum composition remained basically unchanged, XPS analysis showed that the oxygen content decreased and the aluminum content increased, which confirmed that the least metal oxide was formed. The double cleaning method also produced a more uniform surface with lower roughness, which improved the overall surface quality and maintained the integrity of the original material. The surface characterization by SEM, EDS, FT-IR, XPS and TEM confirmed that the original aluminum composition and microstructure were better preserved by double cleaning. The electrochemical corrosion test in 3.5% NaCl solution showed that the corrosion resistance was improved, and the lowest corrosion current reached 4.126 5×10-6 A/cm2. Electrochemical impedance spectroscopy (EIS) analysis provided a deep understanding of corrosion behavior, indicating that the impedance of the samples washed twice was higher, indicating better protection for corrosive ions. The equivalent circuit model used to fit EIS data showed that the double cleaning process led to the formation of a more stable protective oxide layer on the surface, which acted as a barrier for corrosion inhibitors. At the same time, the micro-friction and wear test showed that double cleaning could maintain or even reduce the friction coefficient to some extent. This study emphasizes the potential of laser cleaning, which can effectively remove the paint layer of aluminum alloy while maintaining or improving the surface properties, and can realize the transition from nondestructive cleaning to surface strengthening. Single cleaning is suitable for applications that need protective oxide layer and enhance corrosion resistance, especially in corrosive environment. On the other hand, double cleaning is more conducive to minimizing substrate damage and maintaining surface integrity, making it an ideal choice for applications where surface smoothness, mechanical properties and wear resistance are crucial. Optimizing laser parameters can realize efficient cleaning and surface strengthening, make laser cleaning a promising technology for industrial application, and help to develop more sustainable and effective cleaning technology.
关键词
激光清洗 /
表面形态 /
铝合金 /
单次清洗 /
二次清洗 /
纳秒激光
Key words
laser cleaning /
surface morphology /
aluminum alloy /
single cleaning /
double cleaning /
nanosecond laser
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基金
国家自然科学基金（52275226）;北京市自然科学基金（3222022）
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