Tensile, macrographic and fractographic examinations of friction stir spot welded lap joints of AA5083-H116

Failure of welded materials in lap configuration due to poor adhesion bond or shear strength can lead to catastrophic damage to life and properties. Due to exponential demands for joined or welded components in lap configuration mode, it has become imperative to investigate and understand how a solid state joining process parameter can affect joint efficiency. Thus, this research study focuses on the effect of rotational speed and dwell time on the mechanical properties and the failure mode. Friction stir spot welding was used for the welding process. Three rotational speeds of 600, 900 and 1200 rpm and three dwell times of 5, 10 and 15 secs were used for the welding process. From the mechanical testing of the tensile shear strength, it was noticed that the magnitude of the tensile shear strength (TSS), tensile yield strength (TYS) and the fracture force (F.F.) depend on the choice of the rotational speed and dwell time. The maximum shear strength was found at the mid-rotational speed of 900 rpm. Ductile failure mode was noticed for all the samples during the fractography observations. Visual observation of the keyhole defects revealed that the diameter and depth of the keyhole were influenced by the process parameters, which also impacts the weld integrity and quality.