Enhancing the Corrosion Resistance of ZnAl-LDHs Films on AZ91D Magnesium Alloys by Designing Surface Roughness

Zinc–aluminum layered double hydroxides (ZnAl-LDHs) film is a typical effective corrosion resistant film currently being explored. In this study, ZnAl-LDHs film was prepared on magnesium alloys with different surface roughness by means of metallographic preparation combined with the hydrothermal method. When the surface roughness Sa was at a minimum of 0.094 μm, the ZnAl-LDH films grew the most intensely, reaching 3.8 μm in thickness with a static contact angle of 84.34° and a minimum corrosion current density (icorr) of 1.12 × 10−4 A/cm2. After the neutral salt spray test, the sample mass was only increased by 0.0424 g. The results show that the size of ZnAl-LDHs nanosheets can be tailored by roughness of Mg alloy surface. The low roughness of magnesium substrate can accelerate the growth rate of ZnAl-LDH films, increase the thickness of films, and improve their corrosion resistance, but it is disadvantageous to the excellent hydrophobic properties of the surface. Finally, the possible growth and corrosion prevention mechanisms of LDHs films were proposed. This also provides a theoretical basis for the optimal processing parameters of magnesium alloy surface.