Effect of silane and zirconia on the thermal property of cathodic electrophoretic coating on AZ31 magnesium alloy

Abstract

Magnesium alloys, the lightest structural metal, are used in the field of aeronautics and astronautics more and more, however they are still limited for the poor corrosion resistant and high temperature property. In order to satisfy the need of long time store and short time operation at elevated temperature, coating with excellent corrosion resistance and thermal resistance was prepared on the surface of Mg alloy AZ31B. The cathodic electrophoretic deposition was applied for the preparation of coating. The bonding of organic electrophoretic deposition coating with substrate was improved using silane pretreatment. Nano-ZrO₂ powder treated by silane was added into electrophoretic deposition solution. The corrosion resistance property of electrophoretic coating was evaluated using Machu test, and thermal characteristic using the thermal shock experiment and DTA respectively. The morphology of the coating was examined by SEM. It is found that both the corrosion resistant and thermal shock resistant properties can be improved by modifying the Mg specimen with APS silane, while adding nano-ZrO₂ powder treated by GPS silane to the coating has the optimal effect. And the results also show that the main reason of the coating damage after thermal shock at 400 °C or 500 °C is mainly for the thermal stress.