A Study on Corrosion Behaviour of Magnesium Alloys

A biodegradable Mg-4Zn-0.6Zr alloy with different content of strontium (Sr) was prepared and studied for orthopedic applications biomaterials. The effects of Sr on the microstructure and corrosion degradation of the as-cast Mg-4Zn-0.6Zr-xSr (ZK40xSr) alloys were investigated. The optical micrograph (OM) observation, energy-dispersive spectrometer (EDS), X-ray diffractometer (XRD) and immersion test were used. The grain size of Mg-4Zn-0.6Zr alloys was reduced obviously with the addition of Sr. The excess of Sr would lead to grain size increasing and grain boundaries widening. The possible presence of the following constituent phases in the grain boundaries: α-Mg, Mg17Sr2, MgZn, ZnxSry binary and MgxZnySrz ternary phase. The formation of ZnxSry and MgxZnySrz phase owed to the larger difference of electronegativity values of Zn and Sr. The immersion tests indicated that the average corrosion rate of the as-cast ZK40xSr alloys increased with the increase of Sr content. It contributed to the micro-galvanic corrosion between the α-Mg with the continuous distribution of grain boundaries precipitates.