A study on alkaline heat treated Mg-Ca alloy for the control of the biocorrosion rate

To reduce the biocorrosion rate by surface modification, Mg-Ca alloy (1.4 wt.% Ca content) was soaked in three alkaline solutions (Na₂HPO₄, Na₂CO₃ and NaHCO₃) for 24 h, respectively, and subsequently heat treated at 773 K for 12 h. Scanning electron microscopy and energy-dispersive spectroscopy results revealed that magnesium oxide layers with the thickness of about 13, 9 and 26 μm were formed on the surfaces of Mg-Ca alloy after the above different alkaline heat treatments. Atomic force microscopy showed that the surfaces of Mg-Ca alloy samples became rough after three alkaline heat treatments. The in vitro corrosion tests in simulated body fluid indicated that the corrosion rates of Mg-Ca alloy were effectively decreased after alkaline heat treatments, with the following sequence: NaHCO₃ heated < Na₂HPO₄ heated < Na₂CO₃ heated. The cytotoxicity evaluation revealed that none of the alkaline heat treated Mg-Ca alloy samples induced toxicity to L-929 cells during 7 days culture.