Microstructural Development in Friction Welded AZ31 Magnesium Alloy

Microstructural development of friction welded AZ31 alloy was studied. The microstructures near weld interface consist of mainly three regions that are recrystallized fine-grain, mixed-grain and twin regions. The most impressive microstructural feature is grain refinement. Fine grains whose size was approximately 2 (mu)m were produced at the weld interface due to a hot heavy working, resulting in the increase of micro-Vickers hardness. New fine grains were born at the shear bands that were introduced during the friction and upset processes. The grain size depended on the welding condition, especially the upset pressure. The smaller grains were obtained with higher upset pressure and shorter friction time. Although Hall–Petch relation was basically realized in friction welded AZ31, it is necessary to consider the effect of work hardening.