Effect of Pin Geometry and Tool Rotational Speed on Microstructure and Mechanical Properties of Friction Stir Spot Welded Joints in AA2024-O Aluminum Alloy

In the present study, the effects of pin geometry and tool rotational speed on the microstructure and mechanical characteristics of the AA2024-O FSSW joint were investigated. Two different types of pin geometries, namely cylindrical and step pins, and three different rotational speeds of 900, 1400, and 1800 rpm were used in the friction stir spot welding joint. The microstructure observation, hardness measurements, and shear tests were done. Results show that both pin geometry and rotational speed give a remarkable effect on the microstructure and maximum shear load of the weld joints. For both pin geometries, the hook height and width of the fully bonded region (FBR) increase by increasing the rotational speed. The weld joint produced by a cylindrical pin exhibits higher values in the hook height and width of the FBR than using a step pin. Furthermore, the highest value in a maximum shear load is obtained at a rotation speed of 1400 rpm for both cylindrical and step pins. Another finding is that the maximum shear loads of FSSW joints produced with a cylindrical pin are higher than that made using a step pin.