Dominant role of laser-generated nano-structures on enhancement of interfacial bonding strength by laser surface modification

Abstract

Laser surface modification has been widely applied to the pre-treatment of material surfaces for interface bonding, however, laser-treated surfaces face an inevitable risk of environmental exposure during engineering application, and it remains unclear how laser-induced modifications change under environmental exposure. This study investigates the robustness of laser-treated aluminum surface under typical atmospheric and aqueous environments at different temperature from −40 °C to 80 °C. Although the carbon elemental content and water contact angle greatly fluctuate with exposure environments from 23 at.% to 33 at.%, and from 0° to 148°, respectively, laser-treated surfaces exhibit stable improvement of ∼25 % in bonding strength compared to untreated condition even after 30 days exposure. Notably, hygrothermal exposure of 80 °C and 95 %RH significantly declines bonding strength by ∼45 %, and this strength degradation is accompanied by 1.8 % increase of carbon elemental content and water contact angle of ∼150°. Results reveal that laser-generated nano-structures play crucial role in strength improvement, instead of carbonaceous contaminants and surface polarity, and nanostructure transformation causes an apparent strength degradation and change of fracture mode from cohesive to interface. This work uncovers the dominant role of laser-generated nano-structures in enhancing interfacial bonding strength, and provides supports for engineering application of laser surface modification.