Exploiting an as-extruded fine-grained Mg-Bi-Mn alloy with strength-ductility synergy via dilute Zn addition

Abstract

Here, a new Mg-1Bi-1Mn-0.3Zn (BMZ110, wt%) wrought alloy designed by the dilute addition of Zn subjected to an appropriate extrusion processing that showed an excellent strength-ductility synergy at room temperature. The main results included four aspects as follows: 1) With dilute Zn addition, the as-cast BMZ110 alloy was refined into an approximately equiaxed-grained structure, since the solid solution of Zn provided a relatively high growth restriction factor. 2) The as-extruded BMZ110 alloy exhibited the finer average grain size and weaker basal texture intensity than the as-extruded BM11 alloy without Zn. The co-segregation of Bi and Zn solutes into grain boundaries was observed to impede grain growth during extrusion and further weaken texture intensity. Moreover, Zn atoms incorporated into Mg3Bi2 phases by replacing Bi atoms increasing the nucleation rate of Mg3Bi2 phases and refining their sizes. 3) Compared with the as-extruded BM11 alloy, the as-extruded BMZ110 alloy demonstrated the higher yield strength (~ 283.4 MPa), ultimate strength (~ 366.2 MPa) and elongation-to-failure (~ 26%). The size refinement of grains and second phases contributed to an extra strength increments. Grain boundary segregation enhanced grain boundary cohesion not only reducing the number density of grain boundary cracks, but also activating more slip modes and grain rotation for increasing the ductility. 4) The as-extruded BMZ110 alloy had the higher grain growth resistance than the as-extruded BM11 alloy during annealing. Solute segregation offered an effective obstacle to restrict grain boundary migration enlarging the activation energy (~ 112.2 kJ/mol) and further delaying the grain growth. Therefore, this work will be helpful for the development of new high performance low-alloyed Mg-Bi based wrought alloys to achieve extensive applications in industries.