Mechanical and Microstructural Properties of Friction Spot Joined 5052 and 6111 Al Alloys

Friction spot joining was used to make lap joints on strips of 5052 and 6111 aluminum alloys. The influence of joining parameters such as tool rotation speeds, plunge depths and dwell times on the weld joint properties were evaluated. A wide range of joining conditions could be applied to join Al alloys without defects in the weld except for certain welding conditions with an insufficient heat input. The microstructures and hardness variations in the welds were discussed. The microstructures of welds, corresponding to the pin hole, have dynamic-recrystallized grain similar to stir zone in FSW weld. In hardness distribution, minimum hardness region was located about 6-mm away from the weld center, corresponding to the shoulder radius of the tool. For each weld the results from tensile-shear tests are also presented. For sound joints without defects, tensile shear fractured load of weld joints was higher approximately 230% than acceptable criteria of tensile shear strength of electrical resistance spot-welded joints for aluminum (MIL-W-6858D).