Effect of rare-earth elements on the structures and mechanical properties of Mg-8%Li alloys

The effect of rare earth element (RE) on the structure and mechanical properties of Mg-8mass%Li (α+β) alloys has been investigated. RE formed intermetallic compounds with magnesium. Below 90% rolling reduction Mg-Li-RE ternary alloys showed work hardening behavior which is similar to that of Mg-Li binary alloy, while above 90% rolling reduction they exhibited the work softening probably due to recovery. Isochronal annealing below 373K softened coldrolled Mg-Li-RE alloys. On the other hand, the recrystallization temperature was raised by the addition of RE. Age-hardening due to the precipitation of α phase in β phase was observed in all alloys. Overaging was recognized in Mg-Li binary alloy, whereas not in Mg-Li-RE ternary alloys. These results suggests that RE addition improves the thermal stability of precipitates, resulting in the improvement of elevated temperature strength through aging treatment. The addition of RE tended to increase the tensile strength, but to decrease the elongation.