The Effects of Pin Offset for FSW of Dissimilar Materials: A Study for AA 7075 – AA 6013

Résumé

The trend in welding of dissimilar aluminum alloys oriented to new application techniques to increase the functionality and perform the welding procedure without any problem in the welded joints. The pin profile and process parameters determined for the friction stir welding greatly affect the weldability and strength of the welded joints. In addition, it is also considered that the pin offset is also an effective factor on the strength and microstructure of welded joints. In the present study, aluminum alloys AA 6013–T6 and AA 7075–T651 were welded with the FSW process applying pin offset technique. The changes in the mechanical and microstructural properties were investigated. The onion ring structure was observed in all of microstructure of weld stir zone. Except the welded joint fabricated with the tool rotational speed of 400 rpm for both without pin offset and with offset to retreating side, all the welded joints were fractured at the base metal region and heat affected zone in AA 6013 alloy. The welded joints fabricated with the tool rotational speed of 400 rpm consisted of small and large cavity-type defects. Although defects were found to occur in the welded joints, none of the welded joints were fractured at the SZ during the tensile and bending tests. The ultimate tensile strength and elongation at rupture of the dissimilar FS welded joints were ranged between 164 MPa and 179 MPa, 6.5 and 7.6%, respectively. These defects were found to affect the ductility feature of the welded joints. The pin offset direction was found to affect the volume of parent materials in the stir zone. Hence, the material volume in the onion rings changes and, the hardness distribution is also affected by the changes in the material volume.   Keywords: aluminum alloys, friction stir welding parameters, fracture analysis