Effect of Low Welding and Rotational Speed on Microstructure and Mechanical Behaviour of Friction Stir Welded AZ31-AA6061-T6

In this paper, the effect of welding and rotational speed on microstructural and mechanical properties has been studied. Unlike eutectic reactions, solid-state diffusion can result in the development of a thin layer of intermetallic compounds (IMC) even when the rotation speed stick to 560 rpm. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) were used for microstructural investigation to reveal the grain deformations at weld interface as well as the development of second phase particles. IMCs such as Al12Mg17 and Al3Mg2 were developed in the stir zone (SZ). The initial grain size of base metal (AZ31) was significantly finer as compared to base metal (AA6061-T6), while after processing, the grain size of stir zone became more finer compared to both base metals. The maximum joint strength was obtained at 210 MPa with rotational and welding speed of 560 rpm and 16 mm/min, respectively. Cryo-Charpy impact test was also investigated at four different temperatures, i.e. 25 °C, 0 °C, − 20 °C, and − 40 °C to understand the fracture behaviour at low temperature. Fracture analysis of both tensile as well as impact test has been done to know the mode of failure in both analyses.