Microstructure evolution of a high-strength low-alloy Zn–Mn–Ca alloy through casting, hot extrusion and warm caliber rolling

Abstract

Through casting, hot extrusion and then warm caliber rolling, biodegradable Zn-0.8Mn-0.4Ca alloy exhibits yield strength (YS) of 245 MPa, ultimate tensile strength (UTS) of 323 MPa, and elongation to failure (EL) of 12%. Its strengths are better than most of the existing biodegradable Zn alloys with ELs of 10–15%. So the alloy can be considered as a more competitive candidate for making bone screws or intravascular stents. Ca has a high efficiency of forming CaZn13 phase, the equilibrium volume fraction of which reaches 10.23 vol% with the minor addition of 0.43 wt% Ca. The CaZn13 particles not only impede dislocation motion, but also stimulate recrystallization of Zn grains, resulting in a considerable strengthening effect. The average size of Zn dendrites in the as-cast alloy reaches 289 μm, while that of Zn grains in the as-rolled alloy is 5.0 μm. On the other hand, the minor Ca addition severely decreases the ductility of the Zn-0.8Mn base alloy due to the large size of CaZn13 particles inherited from the as-cast microstructure. Although their average size is reduced to 12.9 μm after the caliber rolling, it is about five times of that of MnZn13 particles. For design and fabrication of Ca-containing Zn alloys in future, refinement of CaZn13 phase should be a matter of vital concern.