Effect of Mn on the mechanical properties, microstructure, and formability of Mg-Sm-Zn-Mn alloys

This study elucidates the effect of Mn addition (0 - 1.0 wt.%) on the microstructure, mechanical properties and formability of the extruded Mg-1.5Sm-1Zn alloys. All alloys developed a fully recrystallized microstructure after extrusion. Notably, increasing the Mn content resulted in significant grain refinement, reducing the average grain size from 20.32 to 12.05 μm, and a concurrent weakening texture, with the maximum intensity decreasing from 17.44 to 9.19 m.r.d. These microstructural modifications led to enhanced yield strength (YS) and ultimate tensile strength (UTS). As Mn content increased from 0 to 1.0 wt.%, the YS and UTS along the extrusion direction (ED) of Mg-1.5Sm-1Zn- x Mn alloy improved from 95.1 to 114.5 MPa and 195.3 to 218.6 MPa, respectively. However, the elongation to fracture (EL) exhibited a distinct anisotropy, it decreased in the ED but increased in the transverse direction (TD). Most importantly, the Erichsen index (IE), a key indicator of formability, was markedly improved from 2.63 to 4.21 mm with the increase in Mn content from 0 to 1.0 wt.%. Mechanistically, this formability enhancement is attributed to the promoted activity of {10-12} tensile twins, the weakening of texture and an increased strain hardening exponent. The synergistic effect of grain refinement, texture weakening and low anisotropic contributed to an optimal combination of strength and formability in the Mg-1.5Sm-1Zn-1Mn alloy.