Enhancing mechanical property and corrosion resistance of Mg-Zn-Nd alloy wire by a combination of SPD techniques, extrusion and hot drawing

Poor formability and corrosion resistance are the limitations that restrict the widespread applications of biodegradable magnesium alloys as surgical staples. In this study fine-grained Mg-2Zn-0.5Nd (ZN20) alloy wire with a diameter of 0.23 mm was fabricated by a combination of equal-channel angular pressing (ECAP), friction stir processing (FSP), extrusion and hot drawing. ECAP could be beneficial to the subsequent deformation by texture weakening, and FSP could improve the corrosion resistance by decreasing the number of second phases. A typical microstructure with similar diameter of matrix grains and second phase particles was observed in ZN20 alloy wire after combined processing of ECAP, extrusion and hot drawing. The strength of ZN20 alloy wire after combined processing of FSP, extrusion and hot drawing was increased from 292 MPa to 392 MPa due to the grain boundary strengthening, precipitates strengthening and texture strengthening. It was beneficial to the ductility by promoting shear band nucleation and inhibiting its prolongation when the diameter of matrix grains and second phase particles was similar, and the ductility was increased by 3.5 times. The immersion test showed that the corrosion rate could be decreased by nearly 31% after combined processing of FSP, extrusion and hot drawing. Grain refinement could improve the corrosion resistance by stabilizing the corrosion product layer, and the smaller amount of second phase also had a positive influence on the corrosion resistance by avoiding the galvanic corrosion.