LAUSR

Abstract In the present study, Friction Stir Welding (FSW) of a Mg-12Li-1Al alloy containing β phase (bcc) was investigated based on response surface methodology (RSM). The effects of rotating speed (RS) and welding speed (WS) on the mechanical and physical properties of the welds were studied. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness and tensile tests were employed to characterize the samples. Microstructural examinations demonstrated an increase in grain size from 19 μm to 73 μm when maximum temperature of the welding process changed from 333 °C to 426 °C, respectively. The top and root surface layers of the weld underwent transformation of Mg-Li β to Mg-Li α, whose fraction was found to decrease with increase in the heat input. The thickness of the phase transformed layer also proved to be less than 0.2 mm, which was discussed based on the role of Li and the alloy phase diagram. In addition, a model was developed based on the regression method, whereby the results of tensile tests could be expressed as a function of RS and WS. Overall, the alloy exhibited successful FSW behavior and the optimum values of RS and WS for FSW were determined.