Exceptional tensile strength-ductility synergy in friction stir processed Mg-Y-Nd-Zr alloy achieved through bimodal grain size distribution

Abstract

For advanced structural and functional applications, achieving a balanced strength-ductility trade-off is crucial. Nevertheless, the enhancement of strength often results in reduction of ductility, a phenomenon more pronounced in nano-grained materials. Although bimodal grain structures offer potential solution to address this issue, their realization generally involve complex processing steps. Herein, a bimodal grain structure was developed in Mg-Y-Nd-Zr alloy through Friction Stir Processing (FSP). The developed microstructure contains ultra-fine grains of about 2 μm interspersed within fine grains of ∼15 μm. The processed specimen displayed an enhanced tensile strength of 195 MPa, while simultaneously achieving an exceptional elongation of 31 %. These remarkable properties are attributed to the distinct bimodal grain structure, which effectively delays the onset of plastic instability, thereby enhancing strength, uniform elongation, and the rate of work hardening.