摘要
采用脉冲激光器对2A12铝合金基体表面涂覆的环氧树脂底漆与丙烯酸聚氨酯面漆进行激光清洗试验,针对激光清洗表面的形貌、粗糙度及元素含量进行分析。结果表明:在激光能量密度和激光扫描速度分别为4.45J/cm^(2)和8mm/s时,能完全去除面漆且底漆保留完好,并获得了最接近底漆层原始厚度的残余漆层;在此激光能量密度下,当激光扫描速度为5.5mm/s时,能完全去除复合漆层,且此时阳极氧化膜层的微观形貌完好,氧元素质量分数约为40%,清洗表面的粗糙度R_(a)=1.138μm。当参数组合为3.56J/cm^(2)和6mm/s时,也能完全去除面漆且底漆保留较好;当激光能量密度为4J/cm^(2)和激光扫描速度为5mm/s时,能完全去除复合漆层,此时阳极氧化膜表面上氧元素的质量分数约为34%。本研究证明了通过选择合适的激光工艺参数组合能够调控激光清洗质量,验证了激光分层清洗的可行性。
Objective A paint layer can be applied to metals to enhance their surface characteristics and service life.To detect the internal defects of key structural components or repaint the damaged paint layer,the original paint layer needs to be removed from the metal surface.Compared with traditional technologies,such as mechanical or chemical cleaning,laser cleaning technology has the advantages of being environmentally friendly and highly efficient,thus attracts immense attention in the recent years.The influence of different parameters on the cleaning effect was discussed in the published literature,including the effect of laser power on the cleaning efficiency and the state of the metal surface after cleaning.In this study,the effects of different laser energy densities and scanning speeds on the cleaning effect of the composite paint layer on the surface of 2A12aluminum alloy were studied.The effects of different combinations of laser process parameters on layer-by-layer cleaning and post-cleaning damage were explored,and the results can help in understanding the feasibility of layer-by-layer cleaning via laser.Methods In this work,the 2A12aluminum alloy was anodized,followed by the paint layers of epoxy primer and acrylic polyurethane top-coat.The pulsed laser exhibited the wavelength,pulse width,and laser scanning galvanometer speed of 1064nm,70ns,3000 mm/s,respectively.A laser paint-cleaning test was conducted using a single pulsed laser with the laser energy density between 1.78and 4.45J/cm^(2),and the laser scanning speed of3--10mm/s.In the experiment,the side length of the square spot was about 1.5 mm.The cleaning process is completely automatic,and the schematic diagram of the cleaning device is shown in Figure 2.The surface roughness,two-dimensional and three-dimensional topographies of the sample were observed using the laser confocal microscope after experiment.Scanning electron microscope was used to observe the microscopic morphology.The microscopic morphology,surface element content after cleaning,and residual thickness were detected by scanning electron microscope,energy spectrum analyzer,and portable eddy current thickness gage,respectively.Results and Discussions Laser cleaning can remove the composite paint layer-by-layer.The quality of laser cleaning gradually increases with an increase in the laser energy density(Fig.4,Fig.5),and the surface roughness first increases and then decreases(Table 3).The quality of laser cleaning gradually increases with the decrease of the laser scanning speed,but too low scanning speed will lead to an increase in the time of laser acting on the surface of the paint layer.Conversely,if the impact energy generated by the laser is too much,it will leads to excessive cleaning,with net cracks appearing on the surface(Fig.6,Fig.7).In the cleaning process,it can be found that the top-coat is gradually removed to expose the primer,which is then gradually removed to expose the metal substrate.Different laser energy densities lead to different degrees of sample surface roughness.The surface roughness first decreases,then increases,and finally decreases with the increase in the laser scanning speed(Fig.8).Comparing the elements of the cleaned surface and the original paint layer,it is found that under different parameter combinations,the three-dimensional morphology of the primer after complete top-coat removal is different(Fig.9),with the thickness of the primer layer well retained(Fig.10).Compared with the original anodic oxide film,the anodic oxide film is well preserved after cleaning,but there is an oxide film damage(Fig.11).The element content analysis shows that the anodic oxide film on the surface after cleaning has no paint residue(Fig.12).Conclusions Both the laser energy density and scanning speed have a greater impact on the cleaning quality.The cleaning quality of the laser gradually becomes better with an increase in the laser energy density or decrease in the laser scanning speed.When the laser energy density and scanning speed are 4.45J/cm^(2) and 8mm/s,respectively,the topcoat can be completely removed and the primer remains intact,with the effect closest to the original thickness of the paint layer.When the laser energy density and laser scanning speed are 4.45J/cm^(2) and 5.5mm/s,respectively,the composite coating can be completely removed with the perfect microstructure of the anodic oxide film.Similar to those of the original anodic oxide film,the oxygen content of about 40%and the surface roughness R_(a)=1.138μm are observed.When the parameter combination is 3.56J/cm^(2) and 6mm/s,the top-coat can also be completely removed,with the primer retained well.When the laser energy density and scanning speed are 4J/cm^(2) and 5 mm/s,respectively,the composite paint layer can be completely removed,and the oxygen content of the anodic oxide film is about 34%.When the combination of parameters is 3.56J/cm^(2) and 4.5mm/s,the anodic oxide film produces elastic vibration stripping.
作者
刘伟军
赵子铭
李强
王蔚
卞宏友
张栋
Liu Weijun;Zhao Ziming;Li Qiang;Wang Wei;Bian Hongyou;Zhang Dong(School of Mechanical Engineering,Shenyang University of Technology,Shenyang,Liaoning 110870,China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2022年第8期134-144,共11页
Chinese Journal of Lasers
基金
辽宁省“兴辽英才计划”项目(XLYC1802038)。
关键词
激光技术
激光清洗
铝合金
复合漆层
表面形貌
工艺参数
laser technique
laser cleaning
aluminum alloy
composite paint layer
surface morphology
process parameters
