Abstract: Mg-Ca alloys are very promising materials for orthopedic applications owing to the beneficial role of Ca in promoting bone formation. However, they are susceptible to corrosion, especially for the localized corrosion caused by the presence of coarse Mg₂Ca second phase. Here, single-phased Mg-Ca alloys fabricated through a unique high-pressure heat treatment were proposed to solve the issue. Through a proper high-pressure solid solution (HPSS) treatment, the maximum solubility of Ca in Mg can be improved to 1 wt.% under the pressure of 4 GPa and above the temperature of 750 °C, which can’t be achieved through traditional solid solution treatment. Compared to the untreated ones, galvanic corrosion between different phases (Mg and Mg₂Ca) was basically avoided in the Ca supersaturated Mg-1Ca alloy (single-phased). Along with corrosion, a high content of Ca released from the matrix tended to redeposit at the corroded surface and combined with O, P, and C, forming an intact Ca/P/O/C-rich layer, which mainly consisted of CaCO₃, Ca₃(PO₄)₂, and Ca(OH)₂. The rapid formation of this intact layer provided an extra shielding effect for the beneath matrix, thus significantly improving corrosion resistance and biocompatibility. On the whole, a uniform corrosion mode was achieved with a 16-fold reduction in corrosion rate, from 1.83 mm/year in bi-phased ones to 0.11 mm/year in single-phased ones. This work provides a feasible approach to fabricate single-phased alloys containing alloying elements with no or limited solid solubility, pursuing better corrosion and biocompatibility performances.

Key words: Biodegradable magnesium, High-pressure solid solution, Solid solubility, Corrosion, Biocompatibility