As the use of aluminum structures grows due to their lightweight properties and sustainability advantages, optimizing bonding technologies is essential for ensuring strong and durable joints. This study systematically evaluates fourteen surface treatment methods applied to aluminum sheets and L-section joints, assessing their influence on adhesion performance. Surface preparation significantly impacted bond strength. Veil sanding combined with Sika® Primer-207 led to an 82 % increase in tensile strength and a 258 % increase in shear strength compared to untreated surfaces. Laser and hot deionized water treatments resulted in the highest measured surface energy (88 mN/m), improving wettability and adhesive-substrate interaction. To analyze bonding performance, a flexible polyurethane adhesive was applied to structural joints, which were tested under tensile and shear stress conditions. The results demonstrated that surface roughness, free energy, and chemical modification strongly influence failure modes. While untreated surfaces predominantly exhibited adhesive failure, optimized treatments shifted failure toward cohesive failure, indicating a stronger interfacial bond. Additionally, the correlation between surface free energy, surface roughness, and adhesive strength was examined to understand their combined effects on joint performance. The findings highlight the importance of selecting appropriate surface modification techniques to maximize adhesion and joint durability. This research provides practical insights for industries relying on aluminum bonding, offering guidance on optimizing surface treatment protocols to enhance structural integrity and long-term reliability in demanding applications.