Recent advances using equal-channel angular pressing to improve the properties of biodegradable Mg‒Zn alloys

Magnesium alloys are of considerable current interest for use as degradable implants due to their unique properties including biodegradability, biocompatibility, low density and adequate mechanical properties. Nevertheless, there is a need to further improve these properties either by alloying or through the use of appropriate processing. Among the different biodegradable Mg alloys now in use, the Mg‒Zn series are of special interest and have been the subject of many research investigations. This is primarily because Zn is an essential element for the human body in addition to its positive effects in improving the mechanical strength and lowering the degradation rate of the implant. The properties of Mg‒Zn alloys may be further improved both through the addition of third and fourth alloying elements such as Ca, Ag, Sn or Sr and/or by thermo-mechanical processing where the latter is more environmentally and economically favorable. In practice, procedures based on the application of severe plastic deformation (SPD) are especially suited to produce fine-grained microstructures with improved mechanical, degradation and cell behavior. Equal-channel angular pressing (ECAP) is a popular SPD technique that has the capability of producing bulk materials that are sufficiently large for use as typical implants. Accordingly, this review is designed to provide a comprehensive summary of the research that has been undertaken on ECAP-processed biodegradable Mg‒Zn alloys.