Tailoring the mechanical and degradation performance of Mg-2.0Zn-0.5Ca-0.4Mn alloy through microstructure design

A novel Mg-2.0Zn-0.5Ca-0.4Mn alloy has been formulated and processed through melt spinning and hot extrusion to enhance its mechanical and degradation properties. Microstructural characterization of rapidly solidified alloy ribbons consolidated by extrusion revealed a fine and fully recrystallized microstructure with average size of 4 µm. The conventionally extruded alloy consisted of several course second-phase strips as coarse as 100 µm, while the extrusion-consolidated ribbons were devoid of any second phases larger than 100 nm. Rapid solidification followed by extrusion processing resulted in significantly randomized texture where the majority of the basal planes were tilted toward transverse and extrusion directions. Such a weak texture resulted in higher activity of basal planes and thereby considerably improved the fracture elongation from 4% to 19%, while retaining relatively high tensile strength of 294 MPa. In addition to high strength and ductility due to the reduced activity of deformation twining during compression, the extrusion-consolidated alloy ribbons showed lower yielding asymmetric ratio than that measured for the conventionally extruded alloy (1.25 versus 1.61). Electrochemical measurements and immersion tests indicated that application of rapid solidification followed by extrusion remarkably reduced the corrosion rate from 2.49 mm/year to 0.37 mm/year due to recrystallization completion and suppression of coarse second-phase formation.