Tool penetration during friction stir spot welding of Al and Mg alloys

The mechanism of tool penetration during friction stir spot welding of Al-alloy and Mg-alloy sheet materials is investigated and is explained as a progression of wear events, from mild wear to severe wear and then to melt wear in material beneath the base of the rotating pin. Melt wear can also occur under the rotating tool shoulder provided that sufficient penetration of the upper sheet occurs during the spot welding operation. The highest temperatures attained during FSW spot welding of Al 6111 and AZ91 base materials are close to the solidus temperatures of each base material and correspond with 0.94Ts (Al 6111) and 0.99 Ts (AZ91) where Ts is the solidus temperature of the material in degrees Kelvin. C 2005 Springer Science + Business Media, Inc.