Effect of Solution Treatment on Corrosion Behavior of AZ91-2%Ca Magnesium Casting Alloy

Abstract

The study is intended to investigate the effect of solution treatment on microstructure and corrosion behavior of AZ91(Mg-9%Al-1%Zn-0.3%Mn)-2%Ca casting alloy. In as-cast state, the AZ91-2%Ca alloy consisted of intermetallic β(Mg 17 Al 12 ), Al 8 Mn 5 and Al 2 Ca phases in α-(Mg) matrix. After the solution treatment, Al within the α-(Mg) matrix was distributed more homogeneously, along with the slight decrease in the total amount of intermetallic compounds. The corrosion resistance of the AZ91-2%Ca alloy was improved after the solution treatment. The microstructural examinations for the solution-treated samples revealed that the better corrosion resistance may well be related to the incorporation of more oxides and hydroxides such as Al 2 O 3 , Al(OH) 3 , CaO and Ca(OH) 2 into the surface corrosion product without dissolution of the intermetallic phases along the grain boundaries.