2015 Volume 56 Issue 1 Pages 54-60
Friction stir spot welding has been adopted to replace resistance spot welding for Al alloys. This study investigates the effects of plunge depth, rotation speed, and welding duration on the microstructural characteristics of the weld, bonding strength and reliability of 5083 Al alloy. Bonding strength is evaluated using a tensile-shear test and the reliability is analyzed using a Weibull model. According to the experimental results, the major difference in the microstructure was the range of the stirring zone (SZ). The range of the SZ and the tensile-shear failure loading (TSFL) were enhanced when the welding duration or plunge depth was increased. The optimal rotation speed changed with plunge depth. Two fracture modes (tearing mode and cup pull-out mode) appeared for all parameter combinations. When the range of the SZ was deep and broad, the cup pull-out mode was the main fracture mechanism. The TSFL of the cup pull-out mode was higher than that of the tearing mode. Furthermore, the Weibull parameters of the cup pull-out mode were higher and the distribution curve shapes were better. Higher plunge depth, longer welding duration, and a suitable rotation speed made the fracture mode of the tensile-shear test be the cup pull-out mode and led to high bonding strength and good reliability.