Application of pulsed Yb: Fiber laser to surface treatment of Al alloys for improved adhesive bonded performance

Abstract

Surface treatment of the Al surface by pulsed Yb: fiber laser has proven to be effective in improving the adhesive bonded performance of sheet Al substrates. This study was conducted to expand the initial investigation to include sheet, extrusion, and cast Al alloys and measure the effect of laser ablation treatment on the bond strength both in ambient and after water soak. It is found that laser ablation treatment improved the joint strength for all three Al alloys through modification of the surface characteristics and exceeded the target bond strength. Moreover, the results after water soak support the conclusion that the laser ablation treatment exhibited a significant improvement in corrosion resistance of the adhesive-bonded Al joints compared to as-received condition and resulted in the required cohesive fracture mode even after water soak. The reason for this is attributed to the retarding effect of rough laser-ablated surfaces on water diffusion along the bonding interface of laser-treated joints. Besides, the improvement of laser ablation treatment on joint strength before and after exposure increases with the laser fluence. The optimized laser fluence for all three Al alloys is 26.3 J/cm2, which is attributed to a higher degree of laser-induced surface modifications.