EXPERIMENTAL INVESTIGATION OF FEMTOSECOND LASER ABLATION AND MICRO-HOLE GEOMETRY IN Al6061/Al₂O₃ COMPOSITES

The study aimed to create good quality micro-holes to improve the efficiency of heat exchangers. Al6061 was chosen as the material for the fabrication of heat exchangers and to improve its strength it was reinforced with 10 wt.% of alumina. The composite was fabricated using stir casting technology. Tensile strength and hardness of the composites were determined. Micro-holes were drilled on the composites using femtosecond laser micromachining center. Parameters like laser fluence, repetition rate, and pulse overlap ratio were varied to find the ablation threshold, hole diameter, and hole depth. The micro-hole features were observed through a profilometer and scanning electron microscopy analysis. On observation, it was found that as the laser fluence increased, the ablation threshold values of the composites decreased. A saturation point was reached in the ablation value as the repetition rate increased. The increase in the laser fluence led to the increase in hole diameter and hole depth at various repetition rates. Increase in the repetition rate decreased the ablation threshold value but increased the hole depth and hole diameter. Better hole geometry was detected at a laser fluence of 2.49[Formula: see text]J/cm 2 and 10[Formula: see text]kHz repetition rate. At high repetition rate and pulse overlap, cracks, and recast layers were observed due to high accumulation of heat in those areas.