Appearance of the Mechanical Plating Formed by Zn-Al Compounding Flake Powders and Its Anticorrosion

摘要

In this study, a comparison of appearance surface and fracture surface of mechanical plating was made, respectively formed by spherical Zn powders and Zn-Al compounding flake powders. It is found that the spherical particles are deposited and embedded on Zn plating. The deformation of granular Zn powders on coating superficial is relatively large, but there is little distortion of globe grain inside the coating, mainly with spheroidicity distorted. Besides, there are obvious gaps between the particles in Zn coating. In contrast, the flake structure granules of Zn-Al plating are densely and compactly laid out with small space. After contacting with air, the plating coat expands owing to aluminum oxidation, leading to the higher position of the plating coat on the cross section than the matrix metal. We then did salt mist test to verify the corrosion resistance of Zn-Al compounding flake coating. It was found that the Zn-Al compounding flake coating was superior to that formed by globe Zn powder. Results show that the addition of layers of flakes has a better shielding action resisting corrosive medium, leading to the decrease of the osmosis from corrosive medium to the coatings. And the coating can repair naturally after being damaged. We further passivate plating with molybdate to improve the anticorrosion of the coating.