Corrosion Behavior of Rapidly Solidified Magnesium-Aluminum-Zinc Alloys

Abstract Rapidly solidified magnesium alloys with 8 at%, 15 at%, and 20 at% Al and 1 at% and 3 at% Zn were fabricated by centrifugal atomization followed by hot extrusion. Microstructure of the alloys was composed of a fine-grain magnesium matrix (0.5 μm) with β-Mg17Al12 precipitates. Electrochemical and weight-loss tests were performed in borate and ASTM D 1384 solution (chloride, carbonate, and sulfate). In both media, corrosion current of the alloys decreased with increases in aluminum or zinc content. In borate solution, a passivating plateau was observed from the corrosion potential (Ecorr) to Ecorr + 1,200 mV. Current density decreased with aluminum and zinc concentrations. Electrochemical behavior of the synthesized matrix and precipitates was characterized. Zinc increased Ecorr of the two phases, with a corresponding decrease of corrosion current. The same trend was noticed for aluminum but with a less dramatic effect. The corrosion mechanism was suggested result from galvanic coupling of the matr...