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.