Surface amorphization of Mg-Zn-Ca alloy by laser rapid melting for orthopaedic applications

The degradation rate of biodegradable Mg alloy is rapid due to the corrosive microdefects including precipitates and grain boundary, limiting its orthopaedic applications. Amorphous Mg alloy does not have these microdefects so low degradation rate, but its plasticity is poor. In this work, a laser rapid melting technique is proposed, which provides a large degree of undercooling to inhibit nucleation and growth, so the surface amorphization of the alloy is obtained to improve corrosion resistance without affecting plasticity. The results show that large quantities of amorphous phases are obtained at the scanning speed between 20 and 120 mm s−1 with the laser power between 80 and 120 W and the scanning passes of 1∼2 after laser rapid melting. The measured microhardness and corrosion rate are higher and 5–10 times slower than that of untreated Mg60Zn35Ca5 alloy respectively, differences that are mainly attributed to the formation of an amorphous phase.