Corrosion behaviour of die-cast AZ91D magnesium alloy in aqueous sulphate solutions

The corrosion behaviour of die-cast AZ91D magnesium alloys in sulphate solutions was investigated by SEM, FTIR and polarization measurements. For immersion times less than 48 h, no pitting corrosion occurred and only generalized corrosion was apparent. According to the polarization curves, the corrosion rate order of the die-cast AZ91D Mg alloy in three aqueous solutions was: NaCl > MgSO4 > Na2SO4. The main corrosion products were Mg(OH)2 and MgAl2(SO4)4·22H2O in the sulphate solutions and the product film was compact. Precipitation of MgAl2(SO4)4·22H2O required a threshold immersion time.