Parametric effect on microstructure evolution, grain size and mechanical behaviour of friction stir butt welding of AA6061-T6 alloy

Abstract

This study examines how friction stir welding (FSW) changes the microstructure and mechanical properties of an AA6061-T6 alloy joint. Results showed that welding speeds (WSs) affected microstructure evolution, joint impact toughness, tensile strength, and ductility. Frictional heat and deformation rate affect grain size and shape. Additionally, the agitated zone on the advancing side had substantially less precipitates than on the retreating side. Tensile strength and impact toughness increased mostly due to high angle grain boundaries (HABs) and grain refining. X-ray diffraction (XRD) results revealed that intermetallic compounds, such as Mg2Si, MgZn2, and Al2CuMg were formed in various regions of stir zone (SZ), whereas β(Mg2Si) and β″(Mg5Si6) were found in Si-rich zones. Impact test revealed a drop in impact energy at all set of parameters when comparing to ambient temperatures (25 °C), i.e. 23%, 20%, and 22% for sample A1 (rotational speed (RS)/WS-710/40), 15%, 24%, and 30% for sample A2 (RS/WS-710/100), and 12%, 7.5%, and 17% for sample A3 (RS/WS-710/160) at 0 °C, −20 °C, and −40 °C, respectively. The maximum joint efficiency of 74.5% was obtained for sample A3. Hardness value was also found to be higher for sample A3 in SZ due to the increase the precipitates and the dislocation densities walls and substructures.