Experimental Investigations into the Mechanical and Metallurgical Characteristics of Friction Stir Welded AZ31 Magnesium Alloy

The microstructural and mechanical behavior of a typical HCP material (AZ31 Mg-alloy) during friction stir welding was studied comprehensively for various sets of parameters. EBSD, SEM, XRD and optical microscopy have been used to characterize the microstructural properties of the welded samples, whereas tensile, microhardness and bending tests have been performed for mechanical behavior. The results showed that a large number of twins and second-phase particles (Mg17Al12 and Mg2Si) were induced. The tendency of intermetallic compounds (IMCs) formations, where both orientations of grain and grain boundaries favored its locations. The localized stress state governed the texture variation during the tension test and it was well described by EBSD analysis in terms of the assumed welding temperature. The average grain size in the stirred zone was obtained 15, 13 and 9 µm which were reduced by 32, 41 and 59%, respectively, with increasing travel speed meanwhile, in thermo-mechanically affected zone grain size was found to be 19.6, 18.2 and 13.2 µm which were reduced by 11, 17 and 40%, respectively. The maximum and minimum bending stress was achieved as 320 and 304 MPa and the corresponding bending angle was 41° and 38°, respectively, for the lowest and highest heat input conditions. All the joints fractured in HAZ-base metal regions with the lowest hardness. The weld strength was improved with travel speed due to reduced recrystallized grains in stirred zone at lower heat input.