Effect of Zn content and processing route on the microstructure, mechanical properties, and bio-degradation of Mg–Zn alloys

Abstract

The effects of zinc content (2 and 4 wt%), heat treatment (solution-treated and T6), as well as hot deformation (extrusion and multi-directional forging (MDF)) on the microstructure, mechanical and degradation behavior of Mg–Zn alloys were studied. As the result of microstructure refinement, solid solution and precipitate strengthening (formation of MgZn second phases), the strength of pure Mg was increased after Zn addition. Solution treatment of the Mg–4Zn alloy resulted in 16% softening due to the dissolution of the MgZn second phases and also grain growth, while aging treatment increased the strength value by 8% in comparison to the as-cast material because of the formation of the fine MgZn2 precipitates. Corrosion tests showed an improvement in the corrosion resistance of Mg due to the Zn addition, which was mainly attributed to the finer microstructure and more stable corrosion film in Mg–Zn alloys. Indeed, the polarization resistance of the as-cast Mg–4Zn specimen in the EIS test increased by about 60% in comparison to pure Mg. Solution-treatment on Mg–4Zn alloy could effectively reduce the degradation rate due to the obtained more uniform microstructure. Hydrogen evolution rate of the extruded and MDF processed Mg–4Zn alloy decreased by 73% and 62%, respectively, in comparison to the as-cast condition. Finer grain size and less volume fraction of precipitates in these two specimens, compared to the as-cast Mg–4Zn specimen, was the main reason of the observed improved behavior.

Keywords

• Biodegradation
• Crystallographic texture
• Mg alloys
• Shear punch test