Effect of a small addition of zinc and manganese to Mg-Ca based alloys on degradation behavior in physiological media

The corrosion of a low-alloy Mg-Ca system was observed in typical physiological media. The specimens were divided into three groups of alloys: binary (Mg-Ca), ternary (Mg-Ca-Zn and Mg-Ca-Mn), and quaternary (Mg-Zn-Mn-Ca). The corrosion of the Mg-Ca based alloys in Tas simulated physiological media was investigated through a potentiodynamic polarization test and a hydrogen evolution measurement test for biomedical applications. An addition of Zn from 0.5 to 1 wt.% in the Mg-1Ca shifted the corrosion potential toward a more positive zone and lowered the corrosion current. On the other hand, an increased amount of Mn from 0.5 to 1 wt.% shifted the corrosion potential toward a more positive zone but increased the corrosion current. The observed microstructure indicated that the distributions of the intermetallic phase and the precipitate played a significant role in the ternary and quaternary alloys. Furthermore, a passive layer on the surface of the Mg alloys that contained Mn assisted in decreasing the current exchange between the environment and the alloys. The quaternary Mg-0.5Ca-0.25Zn-0.25Mn alloy exhibited the lowest hydrogen evolution rate at 0.262 cc/cm²/day. However, an increase in the alloying ratio to Mg-1Ca-0.5Zn-0.5Mn resulted in an increase in the hydrogen evolution rate to 0.752 cc/cm²/day.