Microstructural and mechanical properties of dissimilar joining of AA5052 and AA6061 by friction stir welding

5xxx and 6xxx series alloys are among the most widely used aluminum alloys in various industries, including automobile, shipbuilding and aviation industries. In this research, the joint of two alloys AA6061-T6 and AA5052-H12 was investigated at 4 transmission speeds of 60, 90, 120 and 180 mm/min and 3 rotation speeds of 600, 800 and 1000 rpm. These investigations were carried out in the condition that each of the two alloys was placed in two progressive and regressive sides. The results of these studies showed that the highest tensile strength is when the AA5052 sample is placed on the advancing side and the transfer speed is 90 mm/min and the rotation speed is 600 rpm, and in this case, the final tensile strength value is equal to 197 MPa. In addition, the results showed that, generally, the tensile strength decreases with an increase in the transmission speed at a constant rotational speed, and with an increase in the rotational speed at a constant transmission speed, the tensile strength increases. In addition, microscopic and macroscopic examination of the sections of all samples was performed and various areas and defects were examined. According to the investigations carried out on the microstructure, the grain size in the weld nugget compared to the base metal, HAZ and TMAZ decreases. The grain size in HAZ is the largest in all samples, and this causes a decrease in weld strength in this zone.