The effect of skin characteristics on the environmental behavior of die cast AZ91 magnesium alloy

The skin characteristics of die cast AZ91 magnesium alloys and their consequent environmental behavior were evaluated in correlation with die cast wall thickness. The metallurgical examination of the skins was carried out using scanning electron microscopy (SEM), SPX-surface analyses with ESCALAB 250 apparatus, and X-ray diffraction analysis. The corrosion behavior of the skins was evaluated by immersion tests and by potentiodynamic polarization measurements in 3.5% NaCl solution saturated with Mg (OH)₂ at room temperature. The results show that the corrosion resistance of die cast specimens with relatively greater thickness was improved compared to the corrosion resistance of thin wall specimens. This was explained in light of the obtained skin characteristics, mainly in terms of aluminum content, β phase (Mg₁₇Al₁₂) quantity and morphology, and level of porosity.