Nanosecond laser ablation of Al-Si coating on boron steel

Abstract

Al-Si coating is routinely used for hot-press-forming (HPF) steel to prevent oxidation and decarburization under high-temperature processing conditions. However, the Al-Si coating is not suitable for subsequent welding process and has to be removed before laser welding. In this work, the ablation effect of nanosecond pulse laser parameters (i.e., pulse energy, pulse repetition rate, and pulse number) on Al-Si coating was studied. Experimental results show that for the 100ns pulse duration laser ablation, the complete removal of Al-Si coating requires the pulse repetition rate to be larger than 5kHz and a higher pulse repetition rate needs a smaller pulse number. Despite a statistical ablation threshold in long pulse regime, the calculated ablation threshold of fully removed Al-Si coating was obtained at the laser fluence ~4.4J/cm2 at the pulse repetition rate 25kHz. Due to the accumulation effects, increased pulse number and pulse repetition rate will reduce the ablation threshold. The evolution of ablation depth was simulated using Hirschegg model and a gradual increase and then constant ablation depth was found as the pulse number and pulse repetition rate increase.