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.
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The authors would like to thank the Magnesium Research Institute of Dead Sea Magnesium for the preparation of the die casting specimens, and N. Frumin and D. Mogilyanski from Ben-Gurion University for their kind assistance in the XPS and XRD analyses, respectively.