Improving microstructure and ductility in the Mg-Zn alloy system by combinational Ce-Ca microalloying

A strategy is proposed to enhance the microstructure and mechanical properties of Mg-Zn alloys by combining microalloying additions of the rare earth element Ce and the non-rare earth element Ca. The double additions of Ce-Ca are found to significantly increase tensile elongation compared to binary Mg-Zn, or single additions of either Ce or Ca. Microstructure analysis reveals that the Ce-Ca additions increase ductility by modifying texture and refining grain size. Texture modification is attributed to solute effects from the microalloying elements, particularly Ca, while grain refinement is additionally influenced by a fine dispersion of Mg6Ca2Zn3 precipitates that form during rolling and pin grain boundaries. The microalloying element additions also lead to large secondary phase particles in the alloys, which can limit ductility enhancement by promoting early fracture. By scaling Zn content in the Mg-Zn-Ce-Ca alloys, the Mg6Ca2Zn3 phase fraction and Zn solute content can be controlled for optimum ductility or strengthening potential. (C) 2014 Elsevier B.V. All rights reserved.