Research Progress in Age-Hardenable Mg-Sn Based Alloys

Mg-Sn based alloy system is a typical age-hardenable Mg alloy system with Mg2Sn as the major precipitation phase. Eutectic temperature at Mg-rich end of Mg-Sn phase diagram is much higher than those of Mg-Al and Mg-Zn phase diagrams, which is comparable to that of Mg-RE phase diagram. So Mg-Sn based alloys are hopeful candidates of rare-earth free heat resistant Mg alloys with low cost This paper systematically reviews research progress in age-hardenable Mg-Sn based alloys. The main second phase beta-Mg2Sn has a fcc structure with different lattice parameters reported, one of which the most frequently adopted is a(beta)approximate to 0.676 nm, agreeing well with calculations of interfacial orientations. Twelve orientation relationships (ORs) between Mg2Sn precipitates and Mg matrix have been identified. Those with similar morphologies, i.e., the same long axis direction or the same habit plane, are possibly related to different ORs. Addition of Zn benefits the appearance of beta-Mg2Sn precipitates inclined to the Mg basal plane, which are more effective to hinder dislocation movement on the basal plane and result in a greater strengthening effect. Effects of various alloying elements on age-hardening response and mechanical properties of Mg-Sn binary alloys have been summarized. Elements such as Zn, Al, Ag and Na can enhance age-hardening responses. Due to formation of highly thermal stable compounds with Sn, RE, Ca, Sr and Li exhibit negative effects. Consequently, alloy design of Mg-Sn based alloys faces more difficulties, requiring an in-depth investigation of phase transformation processes. Finally, future research directions have been specified.