Investigations on friction stir weldability of elektron 21 magnesium rare earth alloy

Abstract

newline Elektron 21 (EV31 A) is a Magnesium Rare Earth (Mg-RE) alloy primarily evolved for high-performance applications such as aerospace, automotive, biomedical and several other engineering industries. The excellent properties of EV31A are good castability, low density, high damping capacity, high specific strength, high creep, corrosion resistance, flowability, excellent machinability and ideal weldability properties. One of the efficient and pioneering methods for joining EV31 A and other magnesium alloys is friction stir welding (FS welding). A comprehensive study was conducted to examine the influence of five different FS Welded tool pin profiles, namely Straight Cylinder (SC), Straight Hexagon (SH), Tapered Cylinder (TC), Tapered Hexagonal (TH) and Tapered Square (TS) while the other process parameters such as TRS (600 rpm), welding speed (30 mm/min) and axial force (3 kN) were kept constant. The sound joints were obtained for the selected FS welding process parameters. Microhardness by Vickers microhardness tester, tensile strength by universal testing machine (UTM), macro and microstructural characterization by optical microscope (OM), field emission scanning electron microscope (FESEM) and texture studies by electron backscatter diffraction (EBSD) was performed. Fine-grain size of 2.9 µm was observed at the stirring zone by a TH tool pin with a higher microhardness of 77 HV. Texture studies of TH and TC tool pins showed that a majority of basal planes (gt75%) aligned with the reference direction contributed to the maximum hardness. The maximum tensile strength was found to be 140 MPa (88% of the as-cast alloy) by the iv TH pin profile. FS welds are prone to predominantly ductile fracture and the fractography of the weld has also been studied. In addition, the residual stress of 0.41 GPa for the TH pin profile in the FS Welded sample was obtained by X-ray diffraction (XRD) analysis.