Follow-up ultrasonic vibration assisted laser welding dissimilar metals for nuclear reactor pump can end sealing

Abstract

A novel follow-up ultrasonic vibration assisted welding process was proposed to reduce the common defects in laser welding of dissimilar metals for nuclear reactor pump can end sealing, such as unmixed zone, precipitated phase, and uneven element distribution. The influences of ultrasonic vibration on morphology, microstructure and property of C-276/304 laser-welded joint was analyzed. The results indicated that, the most significant ultrasonic vibration at welding position was achieved at parameters of 25 N pressing force and 13 mm distance from ultrasonic action point to welding position. By the application of follow-up ultrasonic vibration, the width of unmixed zone was reduced and the macro element distribution was homogenized due to the enhancement of molten convection. The average grain radius was refined from 1.03 μm to 0.55 μm because acoustic pressure in the molten pool reduced critical nucleus size rk and caused grain fragmentation. The higher diffusion coefficient and cooling rate caused by ultrasonic vibration suppressed element segregation, and thus the amount of precipitated phase decreased from 2.15% to 0.62%, which finally improved the intergranular corrosion resistance of weld metal. The load capacity of weld joint was improved by 12.6%, and the micro-hardness of weld metal was also increased, attributing to the grain refinement strengthening. The follow-up ultrasonic vibration process proposed in this paper provided an efficient, convenient and widely applicable process for laser seal welding of dissimilar metals for nuclear reactor pump can end sealing with higher qualities.