Investigation of residual stress distribution of dissimilar Al-7075-T6 and Al-6061-T6 in the friction stir welding process strengthened with SiO2 nanoparticles

In this study, residual stress distribution and mechanical properties of friction stir welded dissimilar 7075-T6 and 6061-T6 aluminum alloys were investigated. Welding and rotational speeds were defined using trial and error method in order to reach non-defect welding samples without any crack or cavity. With the selection of H13 steel as the material of the tool, shoulder diameter of 30 mm and Taper Cylindrical Threaded (TCT) pin with 6 mm diameter, non-defect welds achieved. Rotational speeds of 450, 560, 710, 900 RPM with welding speeds of 25, 31.5, 50, 80 mm/min were set together, respectively. In other conditions defects of cavity and low surface quality could be obtained. Contour method was used to determine residual stress distribution at the weld zone. With investigation of the residual stresses distribution, it was observed that they were tensile in the center of the cut sample, and compressive on the edges. Considering the lowest value of yield strength (YS) for the base metal in this research which was 292 MPa for Al-6061-T6 alloy and the highest value of residual stress which was 63.2 MPa, it can be concluded that the residual stress amount is 21.6% of the YS of the base Al-6061-T6 alloy. Also, to increase the metal's yield strength and ultimate tensile strength, SiO2 ceramic nanoparticles used as a reinforcing phase. With adding the SiO2 nanoparticles, the ultimate tensile strength (UTS) increased but the YS and the residual stress decreased.