Microstructure development and biodegradation behavior of additively manufactured Mg-Zn-Gd alloy with LPSO structure

Biodegradable magnesium (Mg) alloy has been considered as a new generation of orthopedic implant material. Nevertheless, local corrosion usually occurs since the severe micro-galvanic behavior among α-Mg and precipitates, and results in too rapid degradation. In this study, porous Mg-Zn-Gd part was fabricated using laser additive manufacturing combined with solution heat treatment. During heat treatment, the precipitated β-(Mg,Zn)3Gd phase dissolved in α-Mg, and reduced the energy threshold of stacking faults on basal planes, which finally triggered the formation of long period stacking ordered (LPSO) phase. The LPSO phases owned minor potential difference with α-Mg, thus causing less micro-galvanic corrosion tendency as compared to β-(Mg,Zn)3Gd phase. More importantly, they were uniformly distributed within the α-Mg grains and showed different orientations between adjacent grains. As a result, the LPSO-reinforced Mg-Zn-Gd tended to expand laterally during corrosion evolution, and achieved uniform degradation with a considerably reduced degradation rate of 0.34 mm/year. Moreover, in-vitro cell tests further proved its favorable biocompatibility. This work highlighted the additively manufactured Mg-Zn-Gd with LPSO structure showed great potential for orthopedic application.