Corrosion Studies of Rapidly Solidified Magnesium Alloys

Effects of alloying elements on the corrosion resistance of mostly binary rapidly solidified (RS) magnesium alloys were examined using electrochemical techniques. Uniform corrosion rates were measured at room temperature in a p H 9.2 sodium borate buffer using electrochemical impedance spectroscopy (EIS). Comparisons of electrochemically and gravimetrically determined corrosion rates of bulk magnesium and magnesium alloys showed that the charge transfer resistance could be used to accurately measure the corrosion rates of these materials provided the attack was indeed uniform. The correlation broke down for pure magnesium, which suffered a nonuniform attack due to the undermining of small particles. Corrosion rate measurements of binary alloys showed that aluminum was the only element which caused a decrease in the corrosion rate of magnesium; the corrosion rate decreased with increasing aluminum content. Low concentrations of zinc and lithium resulted in alloys with corrosion rates slightly higher than that of the pure magnesium. Anodic polarization scans were used to compare as‐cast and rapidly solidified commercial ternary alloy AZ61 in borate ( p H 9.2) and carbonate/bicarbonate ( p H 10.0) buffer solutions containing 100 ppm, 1000 ppm, and 3.5 weight percent sodium chloride. The RS AZ61 formed a more protective film than the cast material under these conditions.