Dense Amorphous Passivation Layer Formed on Aluminum Alloy Surfaces by Femtosecond Laser-Assisted Oxygen-Rich Doping

Aluminum (Al) alloy surfaces are prone to serious corrosion in humid and salt-laden environments, which promotes the development of numerous protective approaches. Although the amorphous state is more conducive to improve corrosion resistance compared with the crystalline state, it still faces coating design problems like insufficient adhesive strength and flaking-off tendency. Here, we propose a strategy of femtosecond laser-assisted oxygen-rich doping to in situ create a dense high-quality passivation layer on Al alloy surfaces. With respect to the femtosecond laser processing in traditional air ambience, the material surface modifications within the oxygen-rich environment demonstrate some distinctiveness. For the ridge area of the laser ablation grooves, the oxidation surface is separated into two layers: the outer region presents a loose and porous appearance similar to the observations in the air ambience, while the inner region exhibits complete and homogeneous oxidation, especially associated with the continuous distribution of the amorphous substance, in sharp contrast to the nanoscale discrete amorphous formation in the air case. Simultaneously, the high degree of material oxidization with the amorphous phase is also developed on the wallside area of the groove valleys, which is much different from the incomplete oxidation in the air ambience. As a result, the measured corrosion current decreases by 49 times to a value of I_corr = 1.19 × 10^-10 A/cm² relative to the laser treatment in the air environment. Such a method offers the prospect for elevating the anticorrosion performance of metal surfaces.