The Effects of Tool Rotational Speed on the Microstructure and Mechanical Properties of Friction Stir Welded 7075-T6 Aluminum Thin Sheet

In the present research, FSW of thin sheets of the 7075-T6 aluminum alloy were investigated. Welding speed was held at 50 mm/min. The tool rotational speeds were 600, 1000 and 1600 rpm. The microstructure was investigated by both transmission electron microscope (TEM) and electron backscattered diffraction scans (EBSD). The results indicated that several phenomena occur instantly during FSW in the stir zone, such as precipitation, continuous dynamic recrystallization (CDRX), grain growth and precipitates dissolution which have a severe effect on the mechanical properties. It could also be concluded that for thin sheet of 7075-T6 aluminum alloy, plastic strain is the dominating factor over heat input of the FSW in determination of the microstructure of the weld zone.