Influence of annealing temperatures on corrosion resistance of magnesium thin film-coated electro-galvanized steel

To improve the corrosion resistance of an electro-galvanized steel sheet, we deposited magnesium film on it using a vacuum evaporation method and annealed the films at 250–330°C. The zinc–magnesium alloy is consequently formed by diffusion of magnesium into the zinc coating. From the anodic polarization test in 3% NaCl solution, the films annealed at 270–290°C showed better corrosion resistance than others. In X-ray diffraction analysis, ZnMg₂ was detected throughout the temperature range, whereas Mg₂Zn₁₁ and FeZn₁₃ were detected only in the film annealed at 310°C. The depth composition profile showed that the compositions of Mg at 270–290°C are evenly and deeply distributed in the film surface layer. These results demonstrate that 270–290°C is a proper temperature range to produce a layer of MgZn₂ intermetallic compound to act as a homogenous passive layer.