Optimization of the aluminum oxide properties for adhesive bonding by laser surface pretreatment

The laser pretreatment of AlMg3 has been conducted to investigate the influence of the fluence on the oxide properties. Therefore, the aluminum surface is pretreated by a fiber laser and subsequently analyzed by SEM, EDX, and XPS. Finally, mechanical measurements are performed on adhesively bonded specimens to study the surface properties produced. For the purpose of comparison, the two state-of-the-art pretreatment methods etching and phosphoric acid anodizing are also investigated. The results show that laser pretreatment changes the properties of the aluminum surface and especially those of the oxide layer. The latter grows in comparison to the natural oxide layer of etched surfaces but does not reach the dimensions of an electrochemically formed oxide layer. Mechanical testing showed that the laser treated specimens reach and exceed the strength values of etched and anodized surfaces, respectively. However, strength after aging does not keep up with the good long-term resistance of anodized aluminum, but it exceeds by far the values obtained for etched surfaces. Overall the study showed that optimizing the oxide layer by laser pretreatment leads to improved adhesion and enhances the strength of adhesively bonded aluminum. Therefore, the laser pretreatment of aluminum is an excellent alternative to wet (electro)chemical processes.