Microstructural Effects on Corrosion of AM50 Magnesium Alloys

The influence of microstructure and aluminum distribution on the corrosion of three different casts of the magnesium AM50 alloy (sand, graphite, die) was studied in 1.6 wt% NaCl solution. The microstructure of the alloys and the distribution of individual elements were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analyzes. Differences in the morphology and distribution of corrosion damage were determined using SEM and confocal scanning laser microscopy. Weight change measurements and electrochemical impedance spectroscopy showed that the corrosion resistance improved in the order sand cast < graphite cast ≪ die cast. This increased resistance was shown to be attributable to the increasing tightness of the α-Mg/β-phase/Al-containing eutectic microstructural network, which led to an improved protection of the surface by Al-enriched eutectic and a decrease in the probability of initiating a major damage site on an α-Mg region with low Al content.