Effect of minor Ca addition on microstructure and corrosion behavior of Mg–Y–Ca alloys

The poor corrosion resistance of magnesium and magnesium alloys limited their industry applications, especially attributed to the loose and porous corrosion product film. Moreover, it is of great importance to improve the corrosion resistance of magnesium alloy by economic and environmental protection methods. In this study, the Mg-Y-Ca alloys prepared by the addition of trace Ca and Y elements showed good corrosion resistance. In addition, the effects of minor Ca on the microstructure and corrosion behavior of Mg-1Y alloy were systematically studied. With the increase of Ca content, the corrosion resistance of Mg-1Y-xCa alloys (x= 0, 0.05, 0.1 and 0.2 wt.%) was found to improve and then decrease. Among prepared Mg-1Y-xCa alloys, Mg-1Y-0.05Ca exhibited the lowest corrosion rate of 0.757 mm/y. The high corrosion resistance of Mg-1Y-0.05Ca can be attributed to the fine grain size, and the formation of a protective corrosion passivation film rich in Y2O3, CaCO3 and (MgCa)CO3. However, the excessive addition of Ca element led to the decline of corrosion resistance, resulting from the mass generated Mg2Ca phase causing serious micro-galvanic corrosion, which destroyed the stability of the corrosion product film and damaged the corrosion protection.