As a candidate material for structural components in nuclear reactors, molybdenum (Mo) alloys require strict control of weld pore defects. This study employs longitudinal laser beam oscillation welding to reduce pore defects in Mo alloy pipe weld joints and investigates the underlying mechanisms of pore formation and elimination. Computerized tomography (CT) scan reveals that both porosity and maximum pore size decrease with increasing oscillation amplitude, while with increasing oscillation frequency, they first decrease and then increase. At the same oscillation speed, higher frequencies tend to lead to higher porosity. The number of pores initially increases and then decreases along the wall thickness direction, with most pores concentrated near the fusion line. Adjusting oscillation parameters cannot change the spatial or size distribution of pores, which conforms with the characteristics of base metal (BM) release-type pores induced by oxygen. Bayesian analysis reveals that the improvement in porosity due to oscillation frequency is more significant than its effect on reducing maximum pore size, while the effects of oscillation amplitude on both are likely comparable. High-speed photographs demonstrate that longitudinal oscillation elongates the molten pool, making the temperature gradient smoother, but excessively high frequencies can lead to molten pool instability. When the Reynolds number exceeds approximately 206.45, qualified weld joints with a porosity below 1% can be achieved. This study provides theoretical guidance for the efficient control of pore defects in Mo alloy welding and deepens the understanding of the relevant physical processes. • Longitudinal oscillation cannot change pore spatial or size distribution in Mo-10Re joints. • Oscillation frequency has a significantly stronger effect on porosity than on the maximum pore size. • Longitudinal oscillation elongates the molten pool and smooths the temperature gradient. • The Re threshold for acceptable porosity is 206.45, higher frequency causes higher porosity at the same oscillation V average
Zhang et al. (Thu,) studied this question.