Investigating the Effect of Calcium Alloying and Electrolyte Medium on the Corrosion Behavior of AZ31 Mg Alloy

Magnesium (Mg) has the lowest density among all the structural materials (Al, Fe); however, the diverse applications of Mg have been hampered by its intrinsic brittleness at room temperature and high corrosion susceptibility. Hence, enormous efforts have been made to design the highly ductile corrosion resistant Mg by alloying or other techniques to catapult its utilization. AZ31 is the most commercially used Mg alloy in the transportation sector, yet its high corrosive nature poses a significant disadvantage among other materials. In this study, the effect of calcium on microstructure and corrosion characteristics of AZ31 were investigated. Microstructure was characterized by electron probe microanalysis, scanning electron microscopy and electron back-scattered diffraction. For investigating the corrosion behavior, open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy were analyzed in NaCl and Na2SO4 electrolyte. The microstructure revealed the formation of (Mg, Al)2Ca in AZ31–0.5Ca. The corrosion rates were observed to be significantly reduced for AZ31–0.5Ca as compared to AZ31 (74.53, 67.33 and 29.01, 49.56 mpy for AZ31 and AZ31–0.5Ca in NaCl and Na2SO4 electrolyte, respectively). Improved corrosion resistance was attributed to segregation of aluminum with calcium to form (Mg, Al)2Ca which reduced β–Mg17–Al12 area fraction.