Influence of ultrasonic spot welding on microstructure in a magnesium alloy

Ultrasonic spot welding was carried out on 2-mm-thick sheets of magnesium alloy. A relationship between the dynamic recrystallized grain size and the Zener–Hollomon parameter was established. The energy level, strain rate and peak temperature played key roles in controlling the grain size of the ultrasonic spot-welded samples. A Hall–Petch-type relationship was established, and microhardness tests showed that the hardness decreased with increasing energy input, owing to increasing grain sizes.