Investigation of the effects of welding parameters on mechanical properties of friction stir welded aa 7075 aluminum alloy

In this thesis, the effects of welding parameters, namely tool rotational speed, welding speed and tool pin configuration on the mechanical and microstructural properties of AA 7075-T651 aluminum alloy plates joined using friction stir welding were investigated. Welding bonds were formed using tools with three different profiled pins; and welding conditions were created by a total of 22 different combinations where welding parameters interact with each other. It was revealed that all friction stir-welded joints were characterized by a basin-shaped stir zone. Among the 22 welded joints, the welded joint exhibiting the highest tensile strength of 382 MPa was processed using a pentagonal pin profiled tool with the process parameters of 400 rpm tool rotational speed and 80 mm/min welding speed. The elongation at rupture was measured to be 6% under this welding condition. All welded joints were subjected to a 90° root bending test. Each welded joint was broken before reaching the 90° bending angle due to the heterogeneous structure in the stir zone. The stir zone of all welded joints was characterized by fine and equiaxed grains due to the effect of dynamic recrystallization. Keywords: AA 7075-T651 aluminum alloy; friction stir welding; mechanical properties; microstructure.