A comparison study of Ce/La and Ca microalloying on the bio-corrosion behaviors of extruded Mg-Zn alloys

The influences of Ca and Ce/La microalloying on the microstructure evolution and bio-corrosion resistances of extruded Mg-Zn alloys have been systematically investigated in the current study. Compared with single Ca or Ce/La addition, the Ca-Ce/La cooperative microalloying results in an outstanding grain refinement, because the fine secondary phase particles effectively hinder the recrystallized grain growth. The coarse Ca2Mg6Zn3 phases promote the formation of Ca3(PO4)2 or hydroxyapatite particles during the immersion process and accelerate the dissolution of the corrosion product film, which destroys its integrity and results in the deterioration of anti-corrosive performance. The Ce/La elements can be dispersed within the conventional Mg7Zn3 phases, which reduce the internal galvanic corrosion between Mg matrix and the secondary phases, leading to an obvious improvement of corrosion resistance. Therefore, the Ca-Ce/La cooperative microalloying achieves a homogenous fine-grained microstructure and improves the protective ability of surface film, which will pave a new avenue for the design of biomedical Mg alloys in the coming future.