Comparison of corrosion resistance of Zn-3%Mg-6%Al coatings under different processes

Abstract

This study investigates the corrosion resistance and microstructural properties of traditional hot-dip Zn-3%Mg-6%Al coatings and blackened Zn-3%Mg-6%Al coatings. The blackened coating, characterized by its uniform black surface, is attributed to oxygen-deficient ZnO_1−x structures formed through a controlled blackening process. XRD analysis reveals the presence of a composite oxide Mg_0.125Zn_0.875O, which contributes to the coating's unique coloration and enhanced electrochemical properties. SEM combined with EDS indicates that O distribution is limited to a depth of 5μm, with Al playing a crucial role in promoting oxide formation. Electrochemical tests in a 3.5% NaCl solution demonstrate that the blackened coating exhibits a significantly lower corrosion current density (1.18 × 10⁻⁷A) compared to the conventional Zn-Mg-Al coating (1.57 × 10⁻³A), indicating superior corrosion resistance. The blackened coating also shows improved surface uniformity, with an average color difference of 0.32, outperforming traditional color-coated sheets. These findings highlight the blackened Zn-3%Mg-6%Al coating as a promising alternative for applications requiring enhanced corrosion resistance and aesthetic appeal.