Abstract
Friction stir spot welding of thixomolded and as-cast Mg-alloys AZ91 is investigated. The temperature cycles within the stir zone and in the TMAZ region are examined using thermocouples. The measured temperatures in the stir zone range from 437°C (710K) to 460°C (733K) (0.98Ts, where Ts is the solidus temperature in degrees Kelvin) in AZ91 spot welds. The stir zone microstructures in AZ91 spot welds typically comprise fine equiaxed α-Mg grains. However, spot welds made at room temperature with a thermal insulating layer introduced between the bottom of the AZ91 test specimen and the upper surface of the steel anvil showed evidence of eutectic segregation, liquid penetration and Liquid Penetration Induced (LPI) cracking in the stir zone.
