Study on the Forming Properties of Evaporated Zn-Mg Coating

Zn-Mg coating was obtained by vacuum evaporation method to deposit a certain thickness of magnesium on the surface of galvanized steel plate, and then was annealed. The coating’s surface microstructure and cross-section were observed by SEM. The phase composition of Zn-Mg coating was analyzed through XRD, and the results showed that the evaporated Zn-Mg coatings are mainly composed of MgZn2 and other zinc-magnesium alloy phases, the cupping test were carried out on the sample, the forming properties of the Zn-Mg coating were studied by salt spray test method, and the phase composition of the coating and the corrosion products of the salt spray test of the coating was analyzed through XRD. We obtained that no red rust appeared on the Zn-Mg coatings after 480 hours of salt spray test after cupping test. The products of salt spray corrosion on the Zn-Mg coating were mainly ZnO, Zn5(OH)8Cl2·H2O, Zn4CO3(OH)6·H2O and Zn5(CO3)2(OH)6, which was analyzed through XRD. Among them, Zn5 (OH)8Cl2·H2O is dense and has good insulation properties, which could suppress cathodic reaction and the formation of loose ZnO, thus making the Zn-Mg coating have stronger molding performance than ordinary galvanized sheet.