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.
Key words
laser cleaning /
surface morphology /
aluminum alloy /
single cleaning /
double cleaning /
nanosecond laser
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Funding
National Natural Science Foundation of China (52275226); The Natural Science Foundation of Beijing Municipality (3222022)
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