Cathodic phosphate coating containing nano zinc particles on magnesium alloy

A technology for preparation of a cathodic phosphate coating mainly containing nano metallic zinc particles and phosphate compounds on magnesium alloy was developed. The influence of cathodic current density on the microstructure of the cathodic phosphate coating was investigated. The results show that the crystals of the coating are finer and the microstructures of the outer surface of the coatings are zigzag at the cathodic density of 0.2–0.5 A/dm2. The content of nano metallic zinc particles in the coating decreases with the increase of the thickness of the coatings and tends to be zero when the coating thickness is 4.14 μm. The cathodic phosphate coating was applied to be a transition coating for improving the adhesion between the paints and the magnesium alloys. The formation mechanism of the cathodic phosphate coating was investigated as well.