Study on the influence mechanism of multi directional ultrasonic vibration on laser cladding

Laser cladding is an emerging surface modification technology, and the cladding layer often suffers from defects such as cracks, inclusions and porosity. To address these challenges, ultrasonic vibration demonstrates effective mitigation of microstructural defects in clad layers. In this study, numerical simulation was used to investigate the transient law of different ultrasonic loading methods on the molten pool during laser cladding process. The study found that the introduction of ultrasonic vibration changed the flow rate of the molten metal and affected the Marangoni convection, which in turn changed the flow rate variation pattern inside the melt pool to some extent. The calculation results show that at 1000 ms, multi- directional ultrasonic vibration increases the peak flow rate of the molten pool from 0.23 m/s without vibration to over 0.36 m/s, significantly enhancing the fluidity of the molten pool. Compared with single-directional ultrasound, multi- directional ultrasound vibration breaks dendrites in growth through strong shock waves generated by cavitation effects, and combined with the vigorous stirring of acoustic flow effects, it achieves a more significant tissue refinement effect. The experimental results show that under the action of multi-directional ultrasound, the microstructure of the cladding layer undergoes a significant transformation from columnar crystals to equiaxed crystals. In addition, the average microhardness of the cladding layer increased from 535.3 HV without vibration to 624 HV, an increase of approximately 16.6%.