High fluence nanosecond laser machining of SiCp/AA2024 composite with high pressure assistant gas

This paper presents a feasibility study on machining SiCp/AA2024 composite using nanosecond fiber laser (λ = 1064 nm) with the rated average power of 20 W and the assistance of 1 MPa Ar gas. Ablation characteristics are investigated with variation of pulse repetition rate (f = 3 ∼ 10 kHz, τl = 200 ns) and pulse width (τl = 4, 13, 20, 30, 50, 100, 200 ns, f = 3 kHz). The ablation morphology measured by scanning electron microscopy (SEM) changed from “coated layer”, “partially coated layer” to “column array” appearance with decreasing pulse repetition rate. An effective ablation of the SiCp/AA2024 composite was demonstrated at 3 kHz repetition rate. By increasing pulse width with a fixed pulse repetition rate of 3 kHz, ablation depth and ablation rate linearly increased, meanwhile, both surface roughness and recast layer thickness saturated. The rate achieved was in the range from 27 nm to 157 nm per pulse, and the resultant roughness from 6.75 μm to 20.60 μm. Ablation mechanism was analyzed from the aspects of high pressure assistant gas, high pulse fluence and high beam overlap of 99.8%. Furthermore, the morphology formation mechanism was discussed considering the competition effect between the time for ablated material escaping from cavity and the pulse interval time of “Δτl=1/f” available for ablation.