Experimental investigation of weld characteristics on submerged friction stir welded 6061-T6 aluminum alloy

Mechanical properties such as fatigue life, corrosion resistance, brittle fracture, hardness and dimensional stability mainly depend on the residual stresses of the welded sample. The main purpose of the research work is measuring the residual stress at different rotational speeds and water heads and correlates the results with its microhardness and its grain size. In the present study, submerged friction welding was conducted at different rotational speeds of 800, 1000 and 1200 rpm and water heads of 10 and 20 mm, respectively, while the welding speed and axial load were maintained constant. Residual stress was evaluated at the center of the nugget zone on the welded samples using the nondestructive of X-ray diffraction method. Normal friction stir welding (without water head) experiments were carried out later at various rotational speeds of 800, 1000 and 1200 rpm for comparing with the results of the SFS welded samples. The results indicate that the value of d-spacing, lattice parameter and residual stress of submerged friction stir welded sample as higher than that of the normal FS welded sample. The grain size of the SFS welded samples is compared with those of FS welded samples using a scanning electron microscopy. SFSW samples exhibit smaller grain sizes compared to the normal FSW.