Effects of Sn addition on microstructure and mechanical properties of Mg–Zn–Al alloys

The microstructures and the phases of the as-cast Mg–6Zn–2Al alloys with Sn additions were characterized by XRD, SEM and TEM. They were composed of α-Mg, MgZn and Mg2Sn in the range of 0.5–3.0 mass% Sn, and no ternary phase was detected. The addition of Sn resulted in the suppression of the eutectic transformation and the refinement of divorced eutectics. The tensile tests showed that a minor addition of Sn contributed to the formation of the dispersed short rod-like Mg2Sn particles and the improvement in the ambient and elevated-temperature strength. However, excessive Sn addition led to the coarsening of Mg2Sn particles, and thus resulted in the decline of strength and plasticity. Fractographic analysis demonstrated that quasi-cleavage fracture was the dominant mechanism of these alloys tested at ambient temperature and 150 °C. Cleavage fracture and quasi-cleavage fracture were preferential at ambient temperature and 150 °C, respectively, with the increment of Sn.