Thermal oxidation induced during laser cleaning of an aluminium-magnesium alloy

During laser cleaning of metallic materials by pulsed lasers surface, modifications can be induced mainly by the transient thermal effect. In ambient conditions an oxidation of the cleaned surface can be detected. The aim of this work was to characterize this transient oxidation that can occur below the laser energy domain leading to any phase change (melting, ablation) of the cleaned substrate. A Q-switched Nd:YAG laser with pulse duration of 10 ns and wavelength of 1064 nm was used for the purposes of this study. For the surface analysis of the treated samples X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were used. It was found that thermal oxidation took place on the aluminium-magnesium alloy during the irradiation in air with a laser energy ranged from 0.6 to 1.4 J cm(-2). It has been demonstrated that this thermal oxidation had the same mechanism as in the case of the steady state thermal oxidation of the aluminium-magnesium alloys even though the laser irradiation was applied only for the very short time of 10 ns. When the laser energy reached the value of 1 J cm(-2), the oxide formed by the thermal oxidation became in a large extent crystalline and its outer part was entirely covered by a continuous layer of magnesium oxide.