Corrosion resistance of phosphated Q345 steel treated by pulsed laser irradiation

Abstract This study proposes a surface treatment method that combines phosphate conversion coating (PCC) and pulsed laser irradiation (PLI), using Q345 steel as the substrate. The composition, surface morphology, cross-sectional structure, film–substrate adhesion, and corrosion resistance of the phosphated film before and after laser irradiation were systematically investigated. The results showed that after pulsed laser irradiation, the main composition of the phosphated film changed from Mn 3 (PO 4 ) 2 ·4H 2 O to Mn 3 (PO 4 ) 2 , while the surface roughness decreased from 1.92 μm to 0.37 μm, indicating increased densification. The shedding rate during scratch testing was reduced from 28.3% to 3.5%, demonstrating a significant improvement in film–substrate bonding strength. Compared to untreated phosphated specimens, laser-irradiated specimens exhibited a smaller corroded area, a 72.4% reduction in corrosion current density, and significantly enhanced corrosion resistance.