Effects of strontium and titanium on the microstructure, tensile properties and creep behavior of AM50 alloys

The microstructure, tensile properties and creep behavior of Mg–5Al based alloys with strontium and titanium additions were investigated. Small additions of strontium mainly dissolved into Mg17Al12 particles and increased the thermal stability and creep strength, since they did not cause the formation of any new phase in the microstructure. Small additions of strontium could refine the as-cast microstructure and improve the mechanical properties. A strontium addition higher than 0.4 wt% could result in Al4Sr phase information, which suppressed the formation of Mg17Al12 phases. Addition of 1% strontium decreased the tensile strength and elongation though improved the yield strength at room temperature. However, greater amounts of strontium can improve the mechanical properties at high temperature. Creep strength of the alloy increased with the strontium content. Further additions of Ti increased the alloy mechanical properties both at room and high temperature though slightly reduce the creep strength. Creep mechanisms of alloys with 0.1% and 1% strontium for different temperature/stress regimes were proposed, which showed that the alloys underwent different creep mechanisms with the change of strontium content. These observations indicated that alloys show two different strengthening mechanisms in the strontium content range of 0.02–1 wt%.