Effect of equal-channel angular pressing on microstructural evolution, mechanical property and biodegradability of an ultrafine-grained zinc alloy

Zinc alloys have become one of the most promising material groups for biodegradable medical implants due to their desirable degradability, excellent biocompatibility, unique atherosclerotic resistance, and modest mechanical performance. Grain refinement is an important strengthening mechanism for such an alloy system to improve the mechanical properties. In the present work, an ultrafine-grained (UFG) zinc alloy (Zn-0.033 Mg, in wt.%) was fabricated by equal-channel angular pressing (ECAP) process. The effect of the ECAP process on microstructural evolution, mechanical properties, and biodegradability of the material was investigated. The results indicated that a large number of sub-boundary and recrystallized-grain structures were generated by continuous and discontinuous dynamic recrystallization during severe plastic deformation. Grain size was significantly refined to an average grain size of 1.36 +/- 0.90 mu m, and the percentage of grains below 1 mu m reached 37.4% after 12 ECAP passes. Simultaneously, the texture was changed from the extrusion direction (ED)parallel to < 0001> fiber texture to a texture with ED deviating 70 +/- 5 degrees away from <0001>. Due to the synergy effect of grain refinement and texture, as well as dislocation strengthening, the yield strength was enhanced to 276 +/- 3 MPa after 12 ECAP passes. However, this was inevitably accompanied by a sacrifice of elongation (8.17 +/- 1.21%). Therefore, an optimal combination of yield strength (250 +/- 22 MPa) and elongation (25.37 +/- 0.79%) at mom temperature was obtained after 4 ECAP passes. Moreover, a low corrosion rate of 0.004-0.01 mm/year in the UFG Zn-0.033 Mg alloy fabricated by ECAP was achieved, which fully satisfies the requirements for biodegradable implant materials.