Surface processing of aluminum alloys using burst ultrafast laser pulses for enhanced wettability modulation and surface adhesion

Burst mode ultrafast laser pulses, an advanced laser source that has drawn significant interest in recent years, remain underexplored for laser surface processing. In this study, a burstmode ultrafast laser with a 40 MHz sub-pulse repetition rate was employed to process 2024-T3 aluminum alloy surfaces for coating adhesion enhancement. The unique “splash-like” hierarchical micro/nanostructures, with elevated ability of surface wettability modulation, were discovered for the first time. The influence of processing parameters on surface morphology and wettability was systematically investigated by SEM imaging, AFM and contact angle measurements. As the number of bursts (N burst ) increases, the surface morphology evolves from laser-induced nanospikes to “splash-like” hierarchical topographies, accompanied by a synchronous increase in surface roughness. N burst = 5, show the most significant ability in wettability modulation and produce the surfaces with highest coating adhesion strength of 14.64 MPa, which is approaching to the intrinsic coating strength and approximately six times of the as-received one of 2.57 MPa. The effects of laser processing on the mechanical properties of the aluminum alloy substrate, including tensile and fatigue performance, were also investigated. Finally, the mechanism underlying MHz-burst laser processing was discussed. This work expands the micro/nanostructures scale by laser processing and demonstrates an efficient, eco-friendly method for aerospace surface treatment.