Enhancing the steam oxidation reactivity of Zn-Al-Mg alloy-coated steel sheets through heat treatment

• Heat treatment promotes the phase transformation of MgZn 2 to Mg 2 Zn 11 , enhancing steam oxidation reactivity. • Increased surface hydrophilicity after heat treatment improves steam interaction and oxidation efficiency. • XPS , SEM, and XRD analyses confirm the formation of a thicker and more uniform oxide layer. Zn-Al-Mg alloy-coated steel sheets are widely used in various industries due to their superior corrosion resistance and mechanical properties. To further enhance their surface properties, steam oxidation treatment has recently gained attention as an eco-friendly method for surface blackening and improving corrosion resistance. However, forming a uniform and dense oxide layer remains challenging due to the heterogeneous microstructure of Zn-Al-Mg coatings. This study investigates the effect of heat treatment as a pre-treatment strategy to improve steam oxidation reactivity. Heat treatment at 300 °C for 10 min, followed by steam oxidation at 140 °C for 1 h, induced a phase transformation from MgZn 2 to the more thermodynamically stable Mg 2 Zn 11 , thereby enhancing surface reactivity. The transformation decreased the contact angle, improving wettability, and increased the oxidation rate, promoting the formation of a thicker and more uniform oxide layer. The improved wettability and increased reaction sites contributed to a more efficient oxidation process. These findings underscore the importance of pre-treatment strategies in optimizing steam oxidation and provide insights into enhancing protective oxide layer formation on Zn-Al-Mg alloy coatings.