Synergistic enhancement of strength and plasticity in Mg-4.0Zn-1.5Mn magnesium alloy by minor Yb addition

Micro-alloying magnesium (Mg) alloys by rare earth elements is an efficient method for enhancing their mechanical properties. This work adds minor Yb (0.1, 0.3, 0.5wt.%) into Mg-4.0Zn-1.5Mn alloy to investigate the grain structure, second phase, and mechanical properties variation. The results illustrate that the grain is refined and the basal texture is weakened by adding Yb element. The addition of Yb to the Mg-4.0Zn-1.5Mn alloy forms the YbZn11 phase, as well as Yb-containing particles enriched with Zn and Mn elements. The presence of Yb-containing phases prevents the occurrence of the MgZn2 and α-Mn phases. Moreover, a segregation region of Zn atoms is also formed near the grain boundaries. The addition of minor Yb to the Mg-4.0Zn-1.5Mn alloy leads to a synergistic improvement in the tensile yield strength (TYS), ultimate tensile strength (UTS), and fracture elongation (FE). The Mg-4.0Zn-1.5Mn-0.5Yb alloy exhibits excellent mechanical properties, specifically a TYS of 289 MPa, UTS of 334 MPa, and FE of 21.9%. The strengthening mechanism primarily arises from three factors: grain boundary strengthening, second phase strengthening, and the Zn atoms segregated at grain boundaries. After adding Yb, the multiple slip systems are activated, especially the prismatic slip and pyramidal slip. The activated slip systems collaborate efficiently to control the plastic deformation, leading to an increased work-hardening ability. Consequently, simultaneous enhancement in both strength and ductility is achieved.