Investigation of the Effect of Tool Offset on the Mechanical Properties of Joint Resulted from Friction Stir Welding of Dissimilar Thickness Parts of 6061-T6 Al Alloy

Friction stir welding parameters such as is rotational speed, traverse speed and axial tool offset play as the main roles in achieving joint properties. In this research the effect of axial tool offset and depth of tool shoulder on the quality and mechanical properties of joint resulted from friction stir welding of 2 mm thickness to 4 mm thickness and 2mm thickness to 6 mm thickness of 6061-T6 Al alloy was investigated. It was shown that tensile strength of joints differs by varying the axial tool offset. When tool offsets there are in the thicker part, large discontinues particles could be observed in the stir zone which caused some cracks at the weld surface and therefore reduced surface quality and mechanical properties of joint. The best surface quality and mechanical properties were resulted from the tool offsetting in thinner part. The depth of tool shoulder is an important factor in heat generation, material extrusion under the shoulder and material flow during friction stir welding. At lower depth of shoulder weaker mechanical properties were observed which may be resulted from lack of sufficient heat generation and material flow at this situation.