Optimization of Operational Parameters in Friction Stir Welding of AA7075-T6 Aluminum Alloy Using Response Surface Method

Response surface methodology was employed to optimize effective factors during friction stir welding of AA7075 aluminum alloy. The effect of operational parameters on the ultimate tensile strength of welded joints was studied. Five levels of the tool rotation speed, the welding speed, the shoulder diameter, and the pin diameter in the range of 350–650 rpm, 35–95 mm/min, and 12–18 and 4–6 mm were investigated using a central composite design. In order to have rotatable and orthogonal design, 36 experiments consisting of 12 center points were conducted. Moreover, the distance of each axial point from the center point was 2. All welded joints were defect free. The statistical model showed that the welding speed and the rotation speed compared to the shoulder diameter and the pin diameter have greater impact on the response. It was found that the joint efficiency of 85% was achievable under the intermediate rotational speeds and the high welding speeds using a tool with the moderate shoulder diameters and the large pin diameters. The joint produced using the rotation speed of 513 rpm and the welding speed of 95 mm/min, the shoulder diameter of 16.1 mm and pin diameter of 5 mm yielded the highest joint strength. This joint had a joint efficiency of about 94%.