Using different strategies to improve properties of the biodegradable Mg–4Li–4Zn alloy

Abstract

Recently, novel super light Mg–Li based alloys have attracted wide attention for potential use as biodegradable implants. However, like most of the biodegradable Mg alloys, Mg–Li alloys suffer from high degradation rate and poor mechanical properties, but the degradation is much faster and thus critical in these alloys. Different strategies have been introduced and used to address these weaknesses, including alloying, heat treatment and severe plastic deformation. However, efficiency of these methods have not been yet evaluated and compared with each other. In this investigation, the effects of alloying (0.5 and 1.0 wt% Ca addition), homogenization heat treatment and multidirectional forging process on the microstructure, biodegradation behavior, and mechanical properties of the as-cast Mg–4Li–4Zn base alloy are evaluated and compared. The obtained results indicate that Ca addition is beneficial to improving both mechanical strength and corrosion resistance of the as-cast base alloy. In addition to microstructural refinement, the addition of Ca resulted in formation of Ca- and Zn-rich precipitates, with a network-like structure, which was found to be beneficial to inhibiting the corrosion progress. Although homogenization treatment led to a slight decrease in mechanical strength, it considerably improved the corrosion resistance, through partial dissolution of precipitates and more uniformity of the as-cast microstructure. Finally, it was found that the multi-directionally forged alloy demonstrated improved mechanical and corrosion properties in comparison with the as-cast alloy, which stemmed mainly from the more uniform distribution of fine secondary phases, as well as the reduced average grain size.