Understanding the mechanisms behind the bonding performance of wire arc coatings

Anodic metals, such as aluminum (Al) and zinc (Zn), are extensively utilized via thermal spraying to form a protective film on structural steel from corrosion. The robustness and durability of thermal spray coatings are significantly influenced by bonding performance, which largely depends on substrate surface roughness and coating thickness. This research assessed the impact of substrate surface roughness and coating thickness on the interfacial bonding performance of wire arc coatings with different coating materials (Zn, Al, and Zn-15Al) on A36 steel surfaces. Pull-off (tensile) and Lap shear (LS) tests were conducted to explore the mechanical properties of metallic coatings adhered to substrates. The pull-off test results demonstrated that thicker coatings formed stronger bonds on coarse surfaces, while thinner coatings performed better on fine surfaces. The LS test showed that pure Al coatings were 25–30 % stronger in shear and fracture elongation than pure Zn coatings. In comparison, Zn-15Al coatings outperformed in shear stress by 15 % over pure Al but exhibited the least resistance to fracture elongation. The effects of substrate roughening, arc spray profiles, and the morphology of the sandblast grits were explored by scanning electron microscopy (SEM) analyses. The elemental composition of the coatings from energy dispersive spectroscopy (EDS) revealed a uniform and continuous coating layer with minimal porosity and oxidation, confirming the effectiveness of thermal spray process. This study contributes to the fundamental understanding of the critical factors in controlling the bonding performance of wire arc coatings, paving the way for the optimization and design framework of metallic coatings.