Strengthening Effects of Tool-Mounted Ultrasonic Vibrations during Friction Stir Lap Welding of Al and Mg Alloys

Ultrasonic assistance in friction stir welding of dissimilar metals has proven efficacious in suppressing intermetallics and enhancing joint quality. In a quest to multiply the ultrasonic effects, a tool-mounted ultrasonic vibration system is used to characterize the welds. The ultrasonic vibrations are enforced in the stirred zone (SZ) along the welding direction. Widely used and industrially applicable AA6061-T6 and AZ31B Mg alloys are taken for experimentation in this study. For a better and in-depth interpretation of ultrasonic effects, weld microstructure characterization is done for various parameters and at different regions of interest. The outcomes suggest the efficacy of acoustic assistance to effectively induce enhanced material turbulence in the SZ and, thus, permit intense intermixing of Al and Mg. The X-ray diffraction and microhardness results diminished β-Al3Mg2 and γ-Al12Mg17 intermetallic compound (IMC) phases and improved weld quality for acoustic joints. Unlike previous studies, the electron backscatter diffraction analysis is added to visualize IMC fragmentation and elimination of the β phase in the ultrasonically treated weld zone. The localized fracture scan of ultrasonic welds resembles deep dimples, signifying a mixed mode of failure.