Achieving preeminent strength-ductility synergy of Mg-1Sb-1Mn alloy via trace co-addition of Sn and Zn

In this study, a novel alloy designing concept, refining grain size and depressing intergranular deformation (inter-GD) simultaneously, is put forward to prepare the Mg alloy with preeminent strength-ductility synergy. A basic alloy, Mg-1Sb-1Mn (SM11), is extruded at 220 degrees C to attain ultrafine microstructure. Thereafter, the co-addition of Sn and Zn is conducted to inhibit the inter-GD which is the softening mechanism of the ultrafine-grained SM11 alloy. Compared with SM11 alloy, the tensile yield strength, ultimate tensile strength and compressive yield strength of Mg-1Sb-1Mn-1Sn-0.2Zn (SMTZ1110) alloy increases from 196 MPa, 245 MPa and 193 MPa-301 MPa, 361 MPa and 273 MPa MPa respectively, without the loss of tensile elongation. With the co-addition of Sn and Zn, the grain size is refined from 1.07 mu m to 0.82 mu m. The narrower network spacing of Mg3Sb2 in the as-cast SMTZ1110 alloy promotes particle-stimulation nucleation during extrusion, resulting in finer grains of the extruded SMTZ1110 alloy. The in-situ experiments unveil that the deformation mechanisms in the SM11 alloy are mixed inter-GD and intragranular deformation, while the deformation mechanisms of the SMTZ1110 alloy shift to the modes predominated by intragranular deformation. The transmission electron microscope results show the segregations of Sn and Zn which pin and stabilize grain boundaries and further depress the inter-GD. Under the combining effects of depressing inter-GD and fine-grain strengthening, the strength of the extruded SMTZ1110 alloy is significantly improved. This study provides new insight into the development of Mg alloy with an excellent balance between strength and ductility.