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.

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.

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=0.608 μm (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].

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 S_a=0.668 μm. With increasing the impulse frequency, the surface roughness decreases and then increases twice, with a minimum value S_a=0.660 μm. As the laser-spot travel speed increases, the surface roughness first increases, then decreases, and finally increases. The minimum roughness is S_a=0.608 μm. For single-pulse energy E=100 mJ, pulse frequency F=9.67 kHz, scanning galvanometer speed V_x=4000 mm/s, and laser-spot speed V_y=6.5 mm/s, the cleaning rate of the oxide film reaches 97.14%, and the surface roughness is S_a=0.608 μm. The roughness is lower than that of the mechanically polished oxide film S_a=1.180 μm. 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.