Bonding technologies have evolved significantly over the past decades, playing a crucial role in the field of joining technologies. To date, however, there is no consensus among research groups as to whether surface texture or surface wettability, or both, affect the strength of bonded joints. Bonded joints, as a bonding technique, are highly dependent on the chemical composition of the adhesive or binder. It is also important to note that the strength and the quality of a bonded joint is greatly influenced by surface adhesion and its related phenomena. From a materials science perspective, surface adhesion is characterised by the level of surface wetting and the total surface energy. In addition, microtopographies and other geometrical features play a key role in bond formation. In this research, the goal is to create controlled microtopographies on DP600 steel surfaces, mainly using femtosecond pulsed laser surface treatment techniques. The ability of adhesives to fill microtopographies specifically, the extent and manner in which micro-scale geometries and structures are filled is also investigated. This allows for the establishment of correlations between the strength of adhesive bonds and the shape characteristics of the microtopography, both in the surface-activated and non-surface-activated states.

This study explores the tensile strength of adhesive joints in steel, focusing on the influence of heat treatment and diverse surface modifications. Results indicate a notable relationship between annealing temperature and tensile strength, with the most favorable outcomes identified at 90 min and 165 °C. Particularly, surfaces treated through turning, sandblasting, and plasma treatment (type C) consistently outperformed other methods. A standout revelation emerged from the turned, sandblasted, and plasma-treated surface (C), showcasing an exceptional tensile strength of 69.06 MPa. Load-holding tests underscored its resilience under diverse load conditions. Surface analyses, including roughness measurements, wetting characteristics, and Scanning Electron Microscope imaging, provided valuable insights into structural transformations induced by different treatments. Chemical composition examinations unveiled significant alterations post-plasma treatment, impacting surface chemistry and contributing to an outstanding tensile strength of 67.63 MPa. In essence, this research offers a glimpse into the nuanced factors influencing adhesive joint strength in steel. The turned, sandblasted, and plasma-treated surface emerges as a promising avenue, sparking further curiosity into the underlying mechanisms propelling superior tensile strength in adhesive joints.