Investıgatıon of the effect of dıfferent pre-treatment on coatıng structure ın hot dıp galvanızıng process

Steel production is increasing every day in the world and studies are gaining momentum to improve the steels produced. Steel materials are doomed to corrode under atmospheric conditions if they are not protected by any method. In corroded steels, cross-section loss will occur over time and the structure will be damaged. This damage creates a loss of national wealth as well as moral consequences. Although there are various corrosion protection methods, the most widely used method is the hot dip galvanizing method, both for its life guarantee and its cost. The hot dip galvanizing method consists of the steps of immersing the steel material, which ensures process suitability, in a molten zinc bath at approximately 450°C after a series of preliminary surface treatments. The preliminary surface treatment includes degreasing, pickling with acid, rinsing, immersion in flux solution and drying. In this thesis, the effect of various preparation methods on the quality of hot-dip galvanized coatings were investigated. Surface treatment prior to coating included chemical acid pickling and mechanical blasting using different abrasives such as steel shot (SA 2.5 and SA 3) and glass beads applied to St52 grade steel. Following these process, surface morphology was analyzed via SEM and metallographic techniques, and experimental data were collected for surface roughness (Ra), contact angle(), surface energy (), residual stress, coating thickness and corrosion resistance. Surface roughness tests showed that steel shot blasting provided the highest Ra values (15.9 µm) and the lowest contact angle (49.5 ), indicating improved wettability. Surface energy results, calculated using models such as Wu, Owens-Wendt and Zisman, confirmed the correlation between low contact angles and high  values. These findings were also theoretically supported by the Wenzel and Young-Dupre models. Coating thickness reached its maximum in the most roughened and energy-rich surfaces, with up to 109.2 µm observed on SA3 steel on glass bead-treated surfaces (-380 MPa), which was interpreted to enhance coating adherence. Corrosion testing (Tafel curves) showed the lowest corrosion current and highest potential on samples prepared with SA3 steel shot blasting, confirming that surface treatment has a significant impact on corrosion behaviour. In conclusion, this thesis demonstrates the influence of surface pretreatment on coating structure through both microstructural and electrochemical evaluation and emphasizes the importance of optimized surface conditions for high quality and durable galvanization.