Effect of heat treatment on corrosion resistance and adhesion property in Zn-Mg-Zn multi-layer coated steel prepared by PVD process

In this study, as the alternatives to the depletion of Zn resources, the Zn-Mg alloy was deposited on a steel substrate by a PVD process. Considering the difference of vapor pressure between Zn and Mg in vacuum condition, Zn, Mg and Zn were sequentially coated by PVD process to form a uniform coating layer, and a heat treatment was separately conducted at 200 °C under vacuum condition. As the heating time increased, the volume fraction of the intermetallic compound phases (Mg₂Zn₁₁ and MgZn₂) gradually increased up to the heat-treated sample for 360 s. From the 0T-bending test, delamination of the coating layer was observed from heat-treated sample for 240 s which is composed of over 85% of the intermetallic compound phases. And from the salt spray test, it is confirmed that the red rust generation time was 624 h in heat-treated sample for 360 s which was composed entirely of Zn-Mg intermetallic compound phases.