Effect of arc ultrasonic vibration on microstructure of joint of plasma arc ‘ in situ ’ welding of SiC p /6061Al

An arc ultrasonic test system consisting of ultrasonic frequency excitation source, isolation coupling device, plasma arc welding power and signal acquisition system was created, successfully obtaining ultrasonic vibration in AC arc. The mechanism of arc ultrasonic on microstructures of joint of SiC_p/6061Al matrix composites in plasma arc ‘in situ’ welding with flux cored wire (alloy composition: Al–15Ti–3Si) as filler metal was investigated. Comparing the weld microstructures without arc ultrasonic and with arc ultrasonic (excitation frequencies: 20, 30, 40, 50, 60 and 70 kHz respectively), it can be found that newborn Al₃Ti phase obviously refined owing to ultrasound, and gradually became coarse with the increasing frequency. When the frequencies were 30, 50 and 60 kHz, Al₃Ti was crushed to granular or block, and uniformly distributed in the weld. When the frequencies were 20, 40 and 70 kHz, Al₃Ti was partially crushed and distributed at the original location along the vertical in the weld. The analysis showed that arc ultrasonic impacted the morphology and distribution of Al₃Ti mainly through cavitations and acoustic streaming, also subjected to ‘resonant wave group’ phenomenon of arc ultrasonic.