Abstract:

The laser cleaning experiment was performed on acrylic-polyurethane composite paint layers above 2A12 aircraft aluminum alloy using nanosecond pulse fiber laser in the process conditions of three different scanning speeds （900， 720， 540 mm/s）. The influences of different scanning speeds on cleaning effect were investigated. The experimental results demonstrate that the topcoat is removed completely and the primer is removed partially when scanning speed is 900 mm/s； the residual primer is further reduced， which induces exposure of the oxide film when scanning speed is 720 mm/s； the paint layer is mostly removed， part of the oxide film is broken down， with the aluminum alloy substrate expose when scanning speed is 540 mm/s. It is showed that the cleaning process presents “ablation-plasma shock-ablation” interactive paint removal mechanism characteristics. Pits are the main cleaning characteristic of ablation mechanism which will make the topcoat colorant （β-copper phthalocyanine） and the functional oxide particles stripped from paint layer and deposited. The plasma shock mainly occurs in the region between two neighboring pits， while the detonation wave produced by plasma shock could cause removal or damage of the paint layer. Ablation and plasma shock， on the one hand， will trigger the transient thermal strain paint removal mechanism， which will cause stress fragmentation or peeling of the residual paint layer； and on the other hand， could make the residual paint layer affected by heat， resulting in part of the radical position rearrangement and replacement.

Key words: laser cleaning, aluminum alloy, composite paint layer, scanning speed, mechanism