Wrapping effect of secondary phases on the grains: increased corrosion resistance of Mg–Al alloys

Abstract

ABSTRACTThe discrete secondary phases usually cause severe galvanic corrosion, thereby resulting in rapid degradation for Mg–Al alloys in orthopaedics application. In this study, CaO was introduced into Mg–Al–Zn (AZ61) alloy via selective laser melting (SLM) to ameliorate the characterisations of the secondary phases, with an aim to improve its corrosion behaviour. Results revealed that CaO reacted with Mg and Al in Mg–Al alloys during SLM, suppressing the formation of coarse Mg17Al12 phase and promoting the formation of (Mg, Al)2Ca phase. Meanwhile, the rapid solidification during SLM promoted the homogeneous precipitation of the second phase. As a result, inert (Mg, Al)2Ca phase homogeneously wrapped the Mg grains, which effectively protected them from the invasion of corrosion solution. Thus, the degradation rate was remarkably reduced from 0.073 to 0.031 mg cm–2 h–1. Furthermore, AZ61-9CaO exhibited good cytocompatibility. This work suggested that AZ61-9CaO was promising candidates for orthopaedics implants.