Removal mechanism of laser cleaning for inorganic thermal control coatings on aluminum alloys

To investigate a novel method for removing thermal control coatings, nanosecond pulsed lasers were used to clean inorganic thermal control coatings on aluminum alloys. This study assessed the surface condition after cleaning at different laser fluences and analyzed the cleaning mechanism. The results showed that the laser cleaning threshold of the coating was 1.44 J/cm2. When the number of laser cleanings was one, there were still coating residues on the surface of the substrate no matter how the laser fluence changed. When the number of cleanings was increased to two, the inorganic thermal control coating on the aluminum alloy could be successfully removed at 5.73, 7.00, and 8.28 J/cm2, while the surface of the substrate would slightly melt and appeared a wavy morphology. It is worth noting that at 8.28 J/cm2, the substrate was gasified and then plasma was generated, causing the appearance of cracks on the substrate surface, which led to the damage of substrate. Additionally, as the laser fluence increased, the cleaning mechanism of the thermal control coating gradually shifted from laser ablation to a combination of laser ablation and plasma impact.