2008 Volume 49 Issue 5 Pages 903-908
Die-cast plates of ASTM (American Society for Testing and Materials) AZ91D magnesium alloy were anodized by DC or AC electrolysis in a solution of phosphate and ammonium salt in which the anodized layer is formed by local discharge, followed by rapid solidification. Salt spray tests of the anodized specimens showed that AC electrolysis increases corrosion resistance and the anodized layers become denser compared with that for DC electrolysis. Tensile strength, elongation, and hardness were also improved by anodization, but higher anodizing bias and the resulting heating caused grain coarsening and a decrease in these properties. For the specimens that displayed remarkable improvement in mechanical properties, a decrease in network precipitates of the β phase was observed. Improvement of mechanical properties is considered to be due to the fine precipitation of β inside the grains of the α phase at moderate temperature.