Achieving high strength-ductility synergy in a dilute Mg-Gd-Zn-Zr alloy with heterogeneous structure via hot extrusion

The common problem of low tensile yield strength (TYS) prevails in high ductility dilute-alloying Mg-RE alloys prepared by traditional hot extrusion. The design strategy of heterostructures in the microstructure of Mg alloys can effectively improve the strength-ductility synergy in mechanical properties, which is expected to break the trade-off dilemma between strength and ductility. In this work, we successfully prepared a series of high ductility as-extruded Mg-Gd-Zn-Zr alloys with all elongations (ELs) greater than 26.0% at room temperature. By controlling the extrusion process and thus introducing heterogeneous fiberous structure, we finally obtained a superior Mg-1.5Gd-0.5Zn-0.5Zr (wt.%) alloy with strength-ductility synergy, which exhibits a TYS of 246 MPa, ultimate tensile strength (UTS) of 274 MPa and an EL of 29.0%. The microstructure examination for the alloy with the heterostructure reveals that the structure consists of alternating filamentous deformed-grain and fine-grain layers. The overall fine grains in the microstructure, a large amount of nanoprecipitates and the relatively high density of residual dislocations contribute to the high TYS of the alloy. The alloy maintaining high ductility is attributed to the activation of multiple slip systems, especially the active and mobile dislocations, the inhibition of the P-type dislocation to B-type dislocation transition, {10 1¯ 2} tensile twinning generated early during tensile testing, and full intergranular slip transfers caused by high geometric compatibility. The present work can further promote the development of dilute-alloying Mg-RE alloys with high strength-ductility synergy.