5083铝合金阳极氧化膜激光清洗工艺研究

Laser Cleaning Technology of Anodized Film of 5083 Aluminum Alloy

采用纳秒脉冲光纤激光器对5083铝合金阳极氧化膜进行清洗,对清洗试样的表面形貌、表面粗糙度、元素组成和含量、清洗率及清洗机制等进行分析。研究表明,脉冲频率影响扫描振镜方向的光斑搭接率,激光行进速度影响清洗方向的光斑搭接率,在过高的激光能量下清除氧化膜时会造成基体二次氧化。工艺参数对表面粗糙度的影响规律不同,表面粗糙度随单脉冲能量的增加先增大后减小,随脉冲频率的增加出现两次先减小后增大,随激光行进速度的增加先增大后减小再增大。当单脉冲能量为100 mJ、脉冲频率为9.67 kHz、扫描振镜速度为4000 mm/s、激光行进速度为6.5 mm/s时,5.27μm厚的氧化膜几乎被清洗干净,表面粗糙度为Sa=0.608μm,优于机械打磨表面粗糙度(1.18μm),清洗率达97.14%,与参数优化前相比清洗率提升了2.43%。激光清除5083铝合金氧化膜的机制为热烧蚀、弹性振动剥离和孔洞爆破。

Objective 5083 aluminum alloy is widely used in aircraft plate weldments and fuel tanks.The presence of anodized film on this alloy strongly impacts the welding quality,making a high-quality removal technique essential.Compared with traditional cleaning methods,laser cleaning characteristically achieves high positional accuracy,strong cohesion,good stability,and low damage.It also avoids generating unwanted residue that changes the surface appearance and roughness of the aluminum alloy,seriously affecting the follow-up welding,coating,and other processes.Differences in the surface appearance of aluminum alloys before and after laser cleaning have been widely studied but without a systematic explanation of the underlying reasons for changes in surface appearance and roughness.This study aims to explore the influence of laser-processing parameters on the cleaning surface appearance,surface roughness,elementary composition,and content changes,as well as to establish a laser cleaning process window for a 5083 aluminum alloy anodized film.Using optimized process parameters,the resulting improved cleaning can provide technical support for follow-up processing techniques.Methods This study uses a 5083 aluminum alloy plate coated with anodized film.First,the anodized film on the alloy surface is cleaned using a pulse fiber laser with different single-pulse energies,impulse frequencies,and spot travel speeds.The changes in the alloy surface morphology and roughness after cleaning are observed using the optical microscopy,laser confocal microscopy,and scanning electron microscopy.The composition and content of the elements on the sample surface are detected using an energy spectrum analyzer equipped with a scanning electron microscope.Finally,the mechanism of the removal of the anodized film on the alloy surface,achieved via laser cleaning,is analyzed.Results and Discussions First,it is concluded that the cleaning effect is optimized for single-pulse energy of 100 mJ and an impulse frequency of 9.67 kHz after analyzing the influence of single-pulse energy and impulse frequency on the cleaning effect.Second,under these conditions,the influence of the laser-spot travel speed on the optimization of the cleaning effect is studied.When the laser spot travels at 12.5 mm/s,the overlap rate of the light spot along the laser cleaning direction is large[Formula(5)],the residence time of the light spot on the oxide film per unit area is short,and large oxide film remains on the surface[Figs.10(f)and 12(f)].As the laser spot travel speed slows down to 6.5 mm/s,the overlap rate of the light spot increases,the surface after removing the oxide film is smooth and flat[Figs.10(c)and 12(c)],the minimum roughness of the surface is Sa=0.608μm(Fig.13),the oxygen content(mass fraction)decreases to a minimum of 3.46%,and the aluminum content(mass fraction)increases to a maximum of 79.98%(Figs.19 and 20).When the laser spot moves slowly,the matrix surface is burned and the piezoglypt is formed[Fig.19(b)].When it moves even more slowly,the bulged overlapping appearance at the edge of the piezoglypt becomes unstable and the wave-like appearance forms[Fig.19(a)].The removal mechanism of oxide film depends on the laser energy and mainly includes thermal ablation and hole blasting assisted by elastic vibration peeling[Figs.15(a),15(c),17(i),18,and 23 and Table 4].Conclusions In this study,the effects of the laser-cleaning process parameters on the surface appearance,roughness,elementary composition,and content of 5083 aluminum alloy after removing anodized film are studied.The pulse frequency affects the light-spot overlapping rate in the scanning-galvanometer direction,and the laser-spot travel speed affects its overlapping rate in the cleaning direction.We conclude that a high impulse frequency or a low laser-spot travel speed produces secondary oxidation.With increasing the single-pulse energy,the surface roughness first increases and then decreases,with a minimum value Sa=0.668μm.With increasing the impulse frequency,the surface roughness decreases and then increases twice,with a minimum value Sa=0.660μm.As the laser-spot travel speed increases,the surface roughness first increases,then decreases,and finally increases.The minimum roughness is Sa=0.608μm.For single-pulse energy E=100 mJ,pulse frequency F=9.67 kHz,scanning galvanometer speed Vx=4000 mm/s,and laserspot speed Vy=6.5 mm/s,the cleaning rate of the oxide film reaches 97.14%,and the surface roughness is Sa=0.608μm.The roughness is lower than that of the mechanically polished oxide film Sa=1.180μm.The laser removal mechanism of the anodized film of the 5083 aluminum alloy mainly involves thermal ablation and hole blasting assisted by elastic vibration peeling.