Improved corrosion resistance and mechanical properties of biodegradable Mg–4Zn–xSr alloys: effects of heat treatment, Sr additions, and multi-directional forging

Abstract

The effects of Sr additions, heat treatment (T4 and T6), and multi-directional forging on the microstructural evolution, mechanical properties and biodegradability of Mg–4Zn–xSr alloys were investigated. Corrosion behavior of the alloys was evaluated by the polarization and hydrogen evolution tests. Shear punch and hardness tests were employed to determine the mechanical properties. It was found that mechanical properties and corrosion resistance of the as-cast Mg–4Zn alloy increased by 0.3 wt% Sr addition. However, further increasing the Sr content not only did not improve the mechanical strength, but also had detrimental effects on the corrosion resistance, due to the increased size and volume fraction of the intermetallic particles. While T4 heat treatment decreased the corrosion current density of Mg–4Zn–0.3Sr alloy from 2.58 to 2.1 μA/cm2, it resulted in some mechanical softening. On the other hand, T6 heat treatment significantly improved mechanical strength of the Mg–4Zn–0.3Sr alloy by about 10 MPa, while its effect on corrosion resistance was minor. Multi-directionally forged Mg–4Zn–0.3Sr alloy also demonstrated improved mechanical and corrosion properties compared to the as-cast condition, which was mainly attributed to the smaller grain size as well as better distribution of the secondary phases.