Impact of the tool shoulder diameter to pin diameter ratio and welding speed on the performance of friction sir-welded AA7075-T651 Al alloy butt joints

Abstract

This study investigates the friction stir welding (FSW) of aluminum alloy 7075-T651, mainly focusing on managing heat generation during the process. The critical parameters influencing heat amount and the material flow including FSW tool shoulder diameter (SD) and travel speed (TS) were investigated. Two far different SD of 10 mm and 20 mm with constant pin diameter (PD) of 5.70 mm that resulted in PD: SD ratios of 1:1.75 and 1: 3.50, respectively, were employed. Furthermore, three different travel speeds of 25, 50, and 75 mm min ^−1 at a constant rotation rate of 600 rpm were used in combination with the two PD: SD ratios. The macrographic and radiographic results indicated that the smallest PD: SD ratio has successfully achieved sound friction stir welded (FSWed) joints for the same travel speeds. Results also indicated that a significant amount of material deformed under a high PD: SD ratioat a high TS of 75 mm min ^−1 , while flash increased with reducing PD: SD ratio.Mechanical properties were compared, revealing that hardness in the nugget zone (NZ) decreased with a lower TS of 25 mm min ^−1 . A small PD: SD ratioallowed for more symmetrical heat distribution, supported by the hardness map. The ultimate tensile strength decreased with increasing TS, and the highest ultimate strength, reaching 319 MPa, was observed with a 1:1.75 ratio and TS of 25 mm min ^−1 . X-ray diffraction analysis (XRD) found an increase in peaks with increasing shoulder diameter and the number of peaks increased with decreasing travel speeds.

Keywords

• friction stir welding
• shoulder diameter ratio
• AA 7075-T651
• welding parameters