This study was carried out to clarify whether it is possible or not to improve the mechanical properties of welds by means of applying ultrasonic vibration to the weld metal. Autogenous weld by TIG process was made on an austenitic stainless steel plate vibrated ultrasonically. The effects of the ultrasonic vibration on the solidification structure and the mechanical properties of the weld were examined. The main results obtained in this study are as follows.
The ultrasonic vibration applied to the weld metal makes the tensile strength of the weld higher than that of the conventional weld. By the ultrasonic vibration, the width of an austenite columnar crystal in the weld metal is decreased and this is likely to be one of the factors to increase the tensile strength of the weld.
The ultrasonic vibration changes the microstructure in the weld metal from cellular dendrite morphology in non-vibrated weld metal to subgrain morphology aligned in the growth direction. The existence of the subgrain boundary is also likely to be one of the factors to increase the tensile strength of the weld.
The ultrasonic vibration decreased the primary dendrite arm spacing in the weld metal, causing the weld strength to increase. The larger the ultrasonic vibration amplitude is, the more conspicuous the above phenomena are.
