Effect of Gd on microstructure, mechanical properties and wear behavior of as-cast Mg-5Sn alloy

Effect of minor Gd addition on the microstructure, mechanical properties and wear behavior of as-cast Mg-5Sn-based alloy was investigated by means of OM, XRD, SEM, EDS, a super depth-of-field 3D system, standard high-temperature tensile testing and dry sliding wear testing. Minor Gd addition has strong effect on changing the morphology of the Mg-5Sn binary alloy. Gd addition benefits the grain refinement of the primary alpha-Mg phase, as well as the formation and homogeneous distribution of the secondary Mg2Sn phase. The mechanical properties of the Mg-5Sn alloys at ambient and elevated temperatures are significantly enhanced by Gd addition. The wear behavior of the Mg-5Sn alloy is also improved with minor Gd addition. The alloy with 0.8% Gd addition exhibits the best ultimate tensile strength and elongation as well as the optimal wear behavior. Additionally, the worn surface of the Mg-5Sn-Gd becomes smoother in higher Gd-containing alloys. The best wear behavior of alloy was exhibited when Gd addition was up to 0.8%, showing a much smoother worn surface than that of control sample. The improvement of tensile properties is mainly attributed to the refinement of microstructure and the increasing amount and uniform distribution of Mg2Sn phase. The larger amount of Mg2Sn phase uniformly distributed at the grain boundary of Mg-Sn-Gd alloys act as a lubrication during sliding, and combined with smaller grain size improve wear behavior of the binary alloy.