Friction stir spot welding of AL5754 material used in automotive industry and investigation of mechanical and microstructural properties

Nowadays, lightweighting studies have gained importance due to emission restrictions in automobiles. This situation led to increase using aluminium alloys in the automotive industry and they have focused on the weldability of these alloys recently. Friction stir spot welding is the derivative of the friction stir welding developed as a solid-state welding technique for combining aluminium alloys. In this research, the effect of tool geometry and tool rotational speed parameters on the microstructure, macrostructure and mechanical properties of the joint Al5754 sheets (thickness 1 mm) that are joined utilizing the friction stir spot welding method were investigated by experimental analysis. Mechanical properties of welds are investigated with tensile shear test and microhardness test. Features of microstructure and macrostructure are investigated with scanning electron microscope that is applied to fracture surfaces and qualitative visual examination, respectively. As a result of these examinations: the maximum values as well as the best values of tensile shear strength, hardness and elongation were observed at the tool rotation speed of 1850 rpm. It is found that experimental configurations with the maximum strength values have the maximum hardness values and elongation values. In accordance with the findings in the macroscopic examination, shear failure, mixed cleavage failure and nugget pullout failure were observed in the experimental configurations. In microscopic examination, ductile fracture was generally found in the test samples.