Effect of T4 and T6 treatment on corrosion of die cast AZ91D magnesium alloys in 3.5% NaCl

The effect of heat treatment on microstructure and corrosion behavior of die-cast AZ91D magnesium alloys in 3.5% NaCl solution was investigated by SEM, EDX, XRD and electrochemical technique. It is found that the distribution ofβphase influences the corrosion morphology. Corrosion occurs preferentially in primaryαphase and presents pitting corrosion feature in die-cast AZ91D. After homogenization of T4 treatment,βphase dissolves inαphase and forms a single phase withαmatrix, and the corrosion form turns to localized corrosion. The attack initiates at local site, expands towards deep direction and produces "digging effect". After artificial aging of T6 treatment,βphase is produced in abundance and provides a great deal of effective micro-cathode for anodic dissolution, and the corrosion form exhibits in general corrosion.