At present, there are few researches on laser -MIG arc hybrid welding with a large butt gap. In this paper, laser-MIG arc hybrid welding is used to weld low-alloy high-strength steel with a thickness of 3mm, and a laser-MIG arc hybrid welding process under large gap conditions is developed. This paper studies the effects of arc voltage, laser-wire distance, and wire feed speed on the gap bridging capability of hybrid welding under different butting gaps were studied. Under the condition of the 1mm butt gap, the influence mechanism of laser-wire distance on weld the weld formation of hybrid welding is analyzed by combining high-speed photography, welding current and voltage waveform, the macroscopic and microscopic morphology of the weld. The results show that there are optimal process parameter values for the effects of arc voltage and laser-wire distance on the gap bridging capability of hybrid welding. Adjusting the laser-wire distance can optimize the energy distribution of laser on the welding wire and weld pool, thus controlling the arc current, voltage, and droplet transition mode, and finally affecting the weld penetration and forming. When the laserwire distance is 0mm, the droplet transition frequency is the fastest, and the droplet transition is a mixture of short circuit transition and liquid bridge transition. At this point, the welding rate is the fastest and the welding process is the most stable. However, by comprehensively integrating factors such as the gap bridging capability and the weld penetration, the optimal processing parameters are obtained when the laser-wire distance is 0.5mm.
To improve the weldability of 6061 aluminum alloy and improve the mechanical properties of welded joints, ultrasonic was introduced into the welding process. The microstructure changes of welded joints under different ultrasonic power were studied, and their effects on the mechanical properties of welded joints were analyzed. The grain size was calculated, and the distribution of precipitated phases was observed by the EBSD technique. The results show that the cavitation and acoustic flow produced by ultrasonic vibration can refine the microstructure of welded joint, reduce the grain size by nearly 50%. It promotes the transition of alloy elements to weld and eliminates the segregation of the strengthening phase to the grain boundary, thus improving the mechanical properties of the welded joint.
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