Effect of the Supplementary Aging Process on the Microstructure and Mechanical Properties of Mg-5Sn and Mg-5Sn-0.5Zn Alloys

This paper presents a novel aging process consisting of two stages: an aging at 250 A degrees C for 12 h and a supplementary aging at 70 A degrees C for 18 h. The ingots of Mg-5Sn and Mg-5Sn-0.5Zn alloys were solution heat-treated for 24 h at 480 A degrees C and then quenched in water. Afterward, aging treatments were performed. To compare the effects of this process on age hardening response of both alloys, other aging treatments were performed at 200 A degrees C for 60 h and at 280 A degrees C for 12 h. The age hardening responses were measured by the Vickers hardness test. The structure of specimens was investigated by XRF, DSC, XRD, and FE-SEM. Also, mechanical properties were determined by tensile test and Charpy impact test. Although by using supplementary aging process, maximum hardness of these alloys is not very different in comparison with single- as well as double-aging processes, the necessary times of aging processes are significantly lower than those at around 90%, 85%, and 50%. After the aging process, the microstructure of Mg-5Sn and Mg-5Sn-0.5Zn alloys consists of alpha-Mg, nano-metric particles of Mg2Sn, and GP-zones. In Mg-5Sn alloy, after supplementary aging process, the yield strength, ultimate tensile strength, and elongation increase to 151.2 MPa, 221.2 MPa, and 8% sequentially. In Mg-5Sn-0.5Zn alloy, the YS, UTS, and elongation increase to 154 MPa, 224 MPa, and 7%, respectively. The impact energy in both alloys is 6.63 J and 7.05 J, respectively.