Research on laser modification of Q235 steel phosphate layer to improve paint adhesion and corrosion resistance

Abstract

This study aims to enhance the paint adhesion and corrosion resistance of zinc-manganese phosphate coatings on Q235 steel through nanosecond pulsed laser surface modification. Conventional zinc-based phosphate films often exhibit loose and porous surface structures, which limit their protective performance in harsh environments. In this study, Q235 steel specimens were initially treated with zinc-manganese phosphating and subsequently modified by a 100 ns pulsed fiber laser. The effects of laser treatment on surface morphology, roughness, phase composition, coating adhesion, and corrosion behavior were systematically analyzed. Laser irradiation transformed the phosphate surface into a crater-like microstructure by dehydrating Zn₃(PO₄)₂·4 H₂O, significantly increasing surface roughness. Consequently, scratch tests indicated enhanced paint adhesion (from 3B to 4B), while electrochemical tests showed a positive shift in corrosion potential and a decrease in corrosion current density. Salt spray tests conducted over 14 days confirmed improved long-term corrosion resistance. These findings demonstrate that nanosecond laser-assisted surface modification is an effective strategy to enhance both the adhesion and corrosion resistance of phosphate coatings. This method provides a scalable, non-contact, and precise approach to improving the durability of coated steel structures. It is highly suitable for marine engineering, construction, and other corrosive environments requiring long-term coating performance.