Investigation of the effect of green laser pre-treatment of aluminum alloys through a design-of-experiments approach

The present study aims to investigate a surface treatment process performed by a pulsed Ytterbium green fiber laser on aluminum 2024 coupons. An evaluation of the process parameters effect as well as a statistical optimization of the process is attempted with the aim to improve the mechanical performance of adhesively bonded joints. The process parameters under investigation are the scanning speed, the pulse frequency and the hatching distance whereas the targeted objectives to be optimized are the surface wettability as well as the quality of adhesion as characterized by the Sessile Drop Technique and the Floating Roller Peel Test respectively. A design of experiments approach is implemented to search as effectively as possible the process parameters space. A Box-Behnken three-level factorial design was used to define the minimum number of experimental trials and build an appropriate test matrix. Finally, Analysis of Variance was implemented to assess the influential parameters. The set of parameters that optimize the objective of high peel strength and surface (super)hydrophilicity were identified following a response surface methodology. In order to understand and evaluate the experimental results and the underlying mechanisms, scanning electron microscopy (SEM) and chemical analysis with X-ray photoelectron microscopy (XPS) of the laser-treated surfaces were performed. In conclusion, it has been demonstrated that the laser surface treatment of aluminum alloy is an extremely promising dry treatment method, capable of improving the performance of adhesive bonding.