Investigation Of Ultrasonic Impact Equipment During Welding And Study On Ultrasonic Impact Effect

In this paper, a new technology is put forward which the welding seam behindthe welding pool is treated by ultrasonic impact equipment during the conventionaltungsten inert gas (TIG) welding process. The introduction of ultrasonic wave intothe welding pool is expected to have an influence on the crystallization of weldedjoint and stomatal behavior.The vibration system of ultrasonic impact equipment was made up of theultrasonic transducer and the ultrasonic horn. The dimensions of vibration systemwere calculated and further optimized by using the finite element analysis softwareANSYS. The resonance frequency and impedance of vibration system met the needsof designing requirements.The experiments of the2A14aluminum alloy butt welding processes with andwithout ultrasonic impact were carried out, the appearances, microstructures andmechanical properties of welded joint were compared and analyzed. The resultshave showed that: the ripple weld could be obtained with ultrasonic impact duringwelding process and periodic crystallization should be turned out during weldsolidification process. Compared with conventional TIG welded joint, themicrostructures of weld central zone and fusion zone in ultrasonic impact weldedjoint have changed from coarse columnar gains to the finer equiaxed grainsmicrostructures. The hardness of fusion zone in ultrasonic impact welded joint ishigher than the routine welded joint as a result of changes in microstructures. SEMobservations of the tensile fracture show that the ordinary weld fracture is brittletypically, however, the fracture of ultrasonic impact weld has both the brittle andplastic character. In the view of the microstructure analysis, the second phasecomponents are broken into pieces by ultrasonic-cavitation effect and distributedmore evenly.On the basis of the kinetics and thermodynamic theory, the microstructurerefinement mechanism and the stomatal behavior in welding pool during weldingprocess with ultrasonic impact are discussed. It is indicated that micro-areasuper-cooling during cavitation bubble expansion and high pressure caused bycavitation bubble explosion lead to the increase of nucleation rate, which isregarded as a main reason why microstructure changes. At the same, the cavitationbubble oscillates constantly because of the ultrasonic cavitation, and gets bigger andbigger by collecting hydrogen content around in the welding pool. However, itbecomes harder for cavitation bubble to escape to the atmosphere if the melt flow is changed because of the introduction of ultrasonic wave, which is the reason why thebigger gas holes occur during weld solidification process.