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

•Blue polyurethane paint could be completely removed without damaging the aluminum alloy surface by using a nanosecond pulsed fiber laser.•For laser cleaning of blue polyurethane paint, ablation, spallation and vaporization induced by the rising temperature of paint are the main mechanisms.•With the increasing of laser fluence, three different surface topographies were formed on aluminum alloy surface, which are discussed.•At high laser fluence, the roughness of substrate surface significantly reduces, which provides a reference for achieving the purpose of polishing the substrate surface while laser cleaning.