Effect of ultrasonic vibration on microstructural evolution and mechanical properties of underwater wet welding joint

The propagation of high-intensity ultrasonic vibration into weld pool can influence on microstructure and mechanical properties of welded joints. This research introduced a hybrid method for improving weld quality by using superimposed ultrasonic vibration on workpiece directly in underwater flux cored arc welding (FCAW). With the purpose of revealing how macrostructure, microstructure and mechanical properties of welded joints are affected by ultrasonic vibration within the weld metal, the present study has been carried out. The results indicated that proeutectoid ferrite, ferrite side plate and acicular ferrite constitute the microstructures of weld metal. Ultrasonic vibration can affect the size and morphology of prior austenite grain during weld pool solidification and eventually accelerate the formation of fine ferrite microstructure of weld metal in high proportion in the subsequently solid-state phase transformation. Excellent balance of high tensile strength and impact toughness is realized as more fine columnar microstructures in weld metal with using ultrasonic vibration. These findings suggest that the addition of ultrasonic vibration is an effective way to improve the tensile strength and impact toughness of weld metal during underwater wet welding.