Ultrafast laser–material interactions in commercial aluminium alloys: Ablation threshold, material removal mechanisms, and surface chemistry under femtosecond laser irradiation

As industries such as aerospace, automotive, and marine adopt new materials and designs, the need arises for advanced processing techniques which can shape this material while achieving required part properties. Aluminum alloys, widely used for their low weight, high strength, and corrosion resistance, still face limitations in hardness, wear resistance, and surface fouling. Surface laser processing offers a method to overcome these limitations. Specifically, femtosecond laser ablation offers a high-precision, low-defect method for surface texturing, capable of producing nano- and microscale features. This study investigates the femtosecond laser ablation threshold and material removal behavior of four aluminum alloys—99% pure Al, AA6061, AA7075, and Scalmalloy®—using a 4 W, 400 fs pulse laser at repetition rates up to 1 MHz. The results show significant variability in feature sizes, with AA6061 exhibiting the largest crater diameters depth for and pure Al displaying the greatest ablation depth (up to 4.1 μm) for the same process parameters. Increasing laser power resulted in a linear increase in ablation depth, while pulse repetition rate exhibited an inverse linear trend with depth, contrary to what would be expected from conventional laser processing. X-ray photoelectron spectroscopy (XPS) revealed that laser processing had minimal impact on surface chemistry, with aluminum oxide remaining the dominant component. Differences in physical properties, such as conductivity, reflectivity, and melting point, were identified as the key factors influencing ablation behaviour. These findings underscore the need for material-specific optimization when developing femtosecond laser-based processing techniques for aluminum alloys.