Mechanical properties and material mixing patterns of friction stir spot welded (FSSW) joints of dissimilar aluminum alloys were investigated.Two aluminum alloys typically used in automotive applications,5052-H32 and 6061-T6,were selected.During the experiment,the process parameters including the z-axis force and torque histories were measured as a function of the tool displacement.The mechanical properties were investigated by microhardness measurements of the joint,and the material mixing in the stir zone was investigated by EPMA.The experimental results illustrate different process parameter histories,material mixing in the stir zone and material properties including microhardness distributions for FSSW joints of dissimilar aluminum alloys,likely due to different mechanical behaviors of the selected aluminum alloys in the FSSW process temperature range. Mechanical properties and material mixing patterns of friction stir spot welded (FSSW) joints of dissimilar aluminum alloys were investigated. Two kinds of typically used automotive applications, 5052-H32 and 6061-T6, were selected. the z-axis force and torque histories were measured as a function of the tool displacement. The mechanical properties were investigated by microhardness measurements of the joint, and the material mixing in the stir zone was investigated by EPMA. The experimental results demonstrate different process parameter histories, material mixing in the stir zone and material properties including microhardness distributions for FSSW joints of dissimilar aluminum alloys, likely due to different mechanical behaviors of the selected aluminum alloys in the FSSW process temperature range.