Material Characteristics and Corrosion Performance of Heat-Treated AI-Zn Coatings Electrodeposited on AZ91D Magnesium Alloy from an Ionic Liquid

This study examined co-deposition of Al and Zn on active AZ91D magnesium alloy using ionic liquid electrodeposition. A room temperature Lewis acidic ionic liquid made of aluminum chloride (AlCl₃) and 1-ethyl-3-methylimidazolium chloride (EMIC) with a mole ratio of 60:40 was used as the bath for pure Al electrodeposition, while the addition of 1 wt% ZnCl₂ to this electrolyte was used for co-deposition of Al-Zn on AZ91D magnesium alloy. The material characteristics and corrosion performance of the as-deposited films formed under various deposition charges and those annealed at 200 and 300°C were investigated. The experimental results showed that both pure Al and Al-Zn coatings provided adequate passivity for the AZ91D magnesium alloy. The re-distribution of the chemical composition after heat-treatment, including the formation of intermetallic compounds, gave rise to an increased microhardness and improved passivation behavior of the Al-Zn coated AZ91D magnesium alloy.