Microstructure, Tensile Properties and Creep Resistance of Sub-rapidly Solidified Mg-Zn-Sn-Al-Ca Alloys

Abstract Microstructures, tensile properties and creep resistances of seven kinds of sub-rapidly solidified Mg-Zn-Sn-Al-Ca alloys were studied. Results show that as for the Mg- x Zn- y Sn-2Al-0.2Ca ( x + y =9, x / y =2, 1 and 0.5, in mass%) alloys, the highest UTS and YTS at RT are obtained with the Zn/Sn mass ratio of 1. The YTS at 150 °C increases but that at 200 °C decreases with the increase of Zn/Sn mass ratio. It is possibly ascribed to the elevated-temperature strengthening of Mg 2 Sn particles since the alloy with the lower Zn/Sn mass ratio contains a higher amount of Mg 2 Sn and a lower fraction of Zn-containing phases. As for the Mg-4.5Zn-4.5Sn-2Al- z Ca ( z =0, 0.2, 0.4 and 0.6) alloys, UTS and YTS increase at first and then decrease with the increase of Ca content at both RT and 200 °C. The strength peaks occur at 0.2% Ca and 0.4% Ca, respectively. Both the initial strain and the steady creep rate decrease with the increase of Ca content below 0.4% Ca at 200 °C under the compression stress of 55 MPa. Minor Ca addition can improve the RT and elevated temperature strength and enhance the compressive creep resistance of the Mg-4.5Zn-4.5Sn-2Al alloy, but reduce the elevated-temperature plasticity. In addition, it also has an obvious influence on the tensile fracture mode, which changes from cleavage to quasi-cleavage at RT and from ductile to quasi-cleavage at 200 °C with the increasing of Ca addition.