Surface morphology and properties of structural steel via laser cleaning with saline solution pretreatment

Abstract

As a novel green cleaning technology, laser cleaning has garnered significant attention. However, its efficacy may be limited for steel structures with deep rust layers formed under prolonged natural environmental exposure. To address this challenge, this study systematically compares the performance of dry laser cleaning, wet laser cleaning and saline solution-laser composite cleaning for rust removal on Q235 structural steel, focusing on surface morphology, roughness, hardness, and microstructural evolution. Results demonstrate that acidic saline solution-laser composite cleaning achieves optimal performance at a pulse frequency of 80 kHz, a laser power of 80 W and 8 cleaning passes, characterized by minimal residual contaminants (Sa = 3.266 µm, Sq = 5.316 µm), uniform surface profiles, and the highest hardness value (192.14 HV). Mechanistic analysis reveals that the acidic solution dissolves rust layers via acidic reactions while generating cracks/pores to enhance laser energy absorption. Subsequent laser irradiation induces localized high temperatures and pressures, vaporizing residual rust and suppressing secondary oxidation through a retained liquid film. In contrast, alkaline cleaning primarily removes oily contaminants via alkaline saponification but exhibits limited rust dissolution due to insufficient Fe³⁺ activation. Dry laser cleaning underperforms due to oxide retention and roughness inhomogeneity. This study proposes a scalable and adaptive rust removal strategy, highlighting the industrial potential of saline solution-laser synergy in complex corrosion scenarios.