Comparison of corrosion behavior of Mg-1.5Zn-0.6Zr and AZ91D alloys in a NaCl solution

The microstructure and corrosion behavior of as-cast Mg-1.5Zn-0.6Zr alloy and a comparative AZ91D alloy were investigated through metallographic observations, X-ray diffraction, electron probe micro-analysis, immersion tests, and cyclic polarization measurements. The Mg-1.5Zn-0.6Zr exhibited a single-phase solid solution characteristic and had fine equiaxed grains, while the AZ91D consisted of alpha-Mg matrix and beta-Mg17Al12 second phases. It was found that Zr is enriched in the center of most grains in Mg-1.5Zn-0.6Zr. Immersion tests showed that the corrosion rate of Mg-1.5Zn-0.6Zr was only about half of that of AZ91D in 5% NaCl solution. The better corrosion properties of Mg-1.5Zn-0.6Zr we owe to the elimination of intensive galvanic corrosion reactions, the formation of much more compact and uniform corrosion films, and the stabilization of magnesium solid solution by Zr. The Mg-1.5Zn-0.6Zr showed a desired uniform corrosion behavior during degradation, which can be reasonably explained by cyclic polarization measurements. The Mg-1.5Zn-0.6Zr alloy displays good corrosion resistance and could be a promising degradable biomaterial.