Influence of thermal treatment on microstructure, mechanical and degradation properties of Zn-3Mg alloy as potential biodegradable implant material

Abstract

© 2015 Elsevier Ltd. In this study, the influence of homogenisation heat treatment effect on Zn-3Mg alloy proposed for biodegradable bone implants was investigated. The alloy was developed via casting process from high purity raw materials and homogenised at 360°C for 15h followed by water quenching. Results revealed that the microstructure of as cast alloy was composed of dendritic structure of Zn-rich phase distributed in segregated pattern within Mg < inf > 2 < /inf > Zn < inf > 11 < /inf > eutectic phase. Exposure to the long duration heating of homogenisation apparently broke the dendrites and transformed them into connected precipitates within the alloy's matrix. Non-equilibrium thermal analysis revealed the formation of Mg < inf > 2 < /inf > Zn < inf > 11 < /inf > eutectic phase which nucleated at 367°C and solidified completely at 354°C. The eutectic coherency point occurred at 368°C and 424s when 30% of solid has precipitated during solidification. Homogenisation resulted into lowering the alloy's tensile strength from 104MPa to 88MPa but improving elongation at fracture from 2.3% to 8.8%. The homogenised Zn-3Mg alloy showed improved corrosion resistance (corrosion rate=0.13mmpy) compared to the as-cast one (corrosion rate=0.21mmpy). The mechanical property and corrosion behaviour of the homogenised alloy seem suitable for biodegradable implant applications.