The microstructure, phase composition and corrosion resistance of phosphate conversion coating (PCC) on AZ91D and Mg-Gd-Y-Zr alloy were investigated to understand the coating formation mechanism. It was found that the Volta potential difference between the second phase and α-Mg provides the main driving force for deposition of MgHPO₄ inner layer. Mg dissolution rate is accelerated in Mg-RE (where RE represents rare earth elements) alloy at the beginning of the treatment, leading to formation of a dense and protective conversion coating on Mg-RE compared to AZ91D Mg. Electrochemical noise signals and H₂ evolution rate (HER) obtained during coating formation process were used to investigate and predict the microstructure and corrosion performance of the conversion coatings. A dense and protective conversion layer is produced if the noise resistance is high and HER is relatively low in the final stage of coating growth.

The influence of SiO₂ particles on the microstructure, phase composition, corrosion and wear performance of plasma electrolytic oxidation (PEO) coatings on AM50 Mg was investigated. Different treatment durations were applied to fabricate coatings in an alkaline, phosphate-based electrolyte (1 g/L KOH + 20 g/L Na₃PO₄ + 5 g/L SiO₂), aiming to control the incorporated amount of SiO₂ particles in the layer. It was found that the uptake of particles was accompanied by the coating growth at the initial stage, while the particle content remained unchanged at the final stage, which is dissimilar to the evolution of the coating thickness. The incorporation mode of the particles and phase composition of the layer was not affected by the treatment duration under the voltage-control regime. The corrosion performance of the coating mainly depends on the barrier property of the inner layer, while wear resistance primarily relies on the coating thickness.