Microstructural refinement and hardness improvement in thin copper sheets using beam oscillated fibre laser welding

In this research work, thin copper sheet joints were fabricated using fibre laser welding with circular beam oscillation. Welding was carried out by varying oscillation frequency and welding speed within a controlled power level. The influence of beam oscillation factors on the physical characteristics of the fusion zone has been examined by X-ray diffraction analysis, conventional microscopy, and advanced microscopic techniques to understand the melt pool behaviour, grain refinement processes, and the thermal response of copper under oscillatory heat input. X-ray diffraction pattern and microstructural observations confirmed dynamic recrystallisation in the fusion zone along with refined grain boundaries and an increase in dislocation density. The grain size of the fusion zone decreased from nearly 42 μm to 18 μm as a result of improving the distribution of heat during welding by means of the beam oscillation technique. This fine-grained structure, along with the higher dislocation level, improved the strength and hardness of the copper sheet. The microhardness increased from 82 HV to 104 HV (approximately 27%), and the tensile strength rose from 160 MPa to 202 MPa. The above results indicate that the fusion zone has good interfacial bonding, refined grain size, and improved thermal stability. The selection of appropriate welding parameters yielded clean welds with improved microstructure, and the overall weld quality was superior.