In this study, the microstructure and mechanical properties of weld of 7075 and 6061 aluminum alloy sheets with a thickness of 5 mm were characterized by friction stir welding. The friction stir welding process was performed with variable rotational speed parameters in the range of 450 rpm to 1400 rpm and variable traverse speed in the range of 20 mm / min to 50 mm / min and the rest of the parameters were considered constant. A tool made of hot-rolled steel H13 with a shoulder diameter 3 times the diameter of the pin was used to perform the welding process. In this study, 6061 alloy was placed on the progressive side and butt welding was performed. Welded specimens were examined by visual inspection and were of good quality. The mechanical properties of the joint were investigated by tensile and microhardness tests in the midline of the weld cross section. Microstructural studies were performed using optical microscopy and scanning electron microscopy (SEM) and sediment analysis was performed by energy dispersive spectroscopy (EDS) on the junction. The results showed that at higher rotational speeds less layer structure was observed and the mixing of alloys in the welding area was better. Sediments dissolved in the stir zone during the welding process and got bigger in the heat-affected zone (HAZ) and thermo-mechanical affected zone (TMAZ). Among the welded specimens, the specimen with 1400 rpm rotational speed and 31.5 mm / min traverse speed parameters had the maximum tensile strength with 317 MPa and the strength eva‎luation of other specimens showed that with increasing rotational speed, the strength up to the maximum value increases and then decreases. Microstructural observations showed that with increasing rotational speed, the size of deformed grains in the stir zone increases. The weakest joint area in welded specimens in terms of hardness and tensile strength, the heat affected zone on the side of the 6061 alloy was eva‎luated so that the lowest amount of hardness between the weld areas and the fracture site of the specimens in the tensile test was related to this area. The fracture surface of welded specimens was trans-granular.

علي شفيعي، ابوذر طاهري زاده

علي اشرفي، قاسم عظيمي روئين