激光清洗铝合金表面复合漆层作用机制

Mechanism for composite paint layer on aluminum alloy surface cleaned by laser

采用纳秒脉冲光纤激光器在3种不同扫描速度(900、720、540 mm/s)工艺条件下,对2A12航空铝合金表面丙烯酸聚氨酯复合漆层进行了激光清洗实验,研究了不同激光扫描速度对清洗效果的影响。实验表明,当900 mm/s时,面漆全部去除,底漆部分去除;当720 mm/s时,底漆余量进一步减少,氧化膜显露;当540 mm/s时,漆层基本除净,但部分氧化膜破坏,基材外露。研究发现,清洗过程形成了“烧蚀-等离子体冲击-烧蚀”除漆机制交互作用的特点,烧蚀会引起漆层中功能性氧化物粒子和面漆着色剂脱漆沉积,凹坑为主要清洗特征;等离子体冲击主要发生在凹坑间隔区间,其产生的爆轰波主要对漆层产生破坏或去除作用;烧蚀和等离子体冲击一方面会触发瞬态加热膨胀除漆机制,使残余漆层发生应力碎裂或剥离;另一方面将使残余漆层受到热影响,导致部分自由基发生位置重排和置换。

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 experi⁃mental 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 abla⁃tion 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.