Removal mechanism of blue paint on aluminum alloy substrate during surface cleaning using nanosecond pulsed laser

This paper presents laser cleaning of blue polyurethane paint on Al-Mg series aluminum alloy substrate by using a nanosecond pulsed laser. Experiments were conducted at the laser fluence of 1.2–8.0 J/cm². The specimen topography and surface chemical composition were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The paint could be completely removed without damaging the substrate at the laser fluence of 3.2 J/cm². Ablation, spallation and vaporization are the main cleaning mechanisms during laser cleaning of the paint. The surface roughness was significantly decreased at higher laser fluence due to surface melting. With the increasing of laser fluence, the scratched grooves on the sample surface turned shallow and three different surface topographies were formed at the laser fluence of 4.8 J/cm², 6.4 J/cm² and 8.0 J/cm². The formation mechanisms of the three surface topographies are discussed, which provides a reference for the purpose of polishing the substrate surface while laser cleaning.