Effect of homogenization on the microstructure, biocorrosion resistance, and biological performance of as-cast Mg-4Zn-1Ca alloy

The effect of homogenization treatment on the microstructure, and corrosion resistance, and biological performance of as-cast Mg-4Zn-1Ca alloy had been investigated in this work. The results revealed that the net-like Ca2Mg6Zn3 phase with porous feature was formed in as-cast sample, but it was transformed into compact one after homogenization treatment at 400 ?C for 12 h. Meanwhile, a unit cell encircled by the net-like Ca2Mg6Zn3 phase in as-cast sample is extended to a large one for as-homogenized sample, but the mechanical properties present a trivial variation for the two samples. However, the corrosion resistance of as-cast Mg-4Zn-1Ca alloy in Hank's solution at 37 ?C was remarkably improved via homogenization treatment. For the as-cast sample, corrosion initiates at the porous Ca2Mg6Zn3 phases and gradually propagates toward the surrounding matrix. As a result, a sever corrosion damage occurred due to the presence of micro-galvanic effect and the absence of barrier effect arising from porous Ca2Mg6Zn3 phases. The enhanced corrosion resistance of as-homogenized sample was mainly ascribed to the barrier effect of compact Ca2Mg6Zn3 phases even though micro-galvanic effect and localized corrosion occurs. Moreover, the as-cast Mg-4Zn-1Ca alloy and as-homogenized samples showed a little cytotoxicity to rat bone marrow stem cells (rBMSCs). rBMSCs cultured with the as-homogenized sample exhibited better osteogenesis-related gene expression. As such, with improved corrosion resistance and osteogenic differentiation ability, as-homogenized Mg-4Zn-1Ca alloy is potential for orthopedic applications.