Investigation on the adhesion improvement of organic coatings on the surface of hot-dip galvanized steel

Abstract

In order to solve the problem of poor adhesion of organic coatings on the surface of hot-dip galvanizing, we conducted a series of experiments to select the suitable pre-treatment method and type of the coatings. We adopted temperature shock & alternating damp heat combined test and waterproof test to simulate the service conditions, and investigated the adhesion of organic coating on the surface of hot-dip galvanizing in the wet environment. With the XPS analysis, we discussed the avoidance of formation of weak boundary layer on the hot-dip galvanizing surface by pre-treatment, and the improvement on adhesion of the organic coatings. We also proposed the pre-treatment method of coupling treatment with silane or combined alkali washing & grinding procedures, by which the organic coating on the hot-dip galvanizing surface performed excellent adhesion and water proof ability against wet conditions.

Multiscale and Multi-Technical Approach to Characterize the Hot-Dip Galvanized Steel Surface and Its Consequence(s) on Paint Adhesion and Tendency to Blistering

“…In the second case, the loss of adhesion is attributed to the accumulation of water at the interface which induces swelling and internal stress. If the presence of remaining native aluminum oxide on the surface hindered the correct formation of the pretreatment layer as depicted in the literature [8,[12][13][14][15][16][17], it can be supposed that it can lead to an incomplete layer and thus to a weaker interface with reduced stability towards water. In addition, the native aluminum oxide on the surface of HDG steel is known to be inert and to form weaker bonds towards organic molecules [2,8,12,14,41].…”

“…Indeed, Cr-free pretreatments do not have a self-healing ability and rely mostly on a barrier type of protection. As the presence of the inert native aluminum oxide is known to impede the formation of a protective pretreatment layer, it was possible that the performance obtained in the QCT was linked to the inhomogeneity induced by the presence of any remaining inert aluminum native oxide film [8,[11][12][13][14][15][16][17]. According to Saarimaa et al [12], an inhomogeneous distribution of the pretreatment layer can promote the absorption of water and oxygen through the pore of the coating by the increased reactions occurring between anodic and cathodic sites created by their inhomogeneity.…”

“…In addition, to affect the adhesion properties of the complete system, the surface state of HDG steel will also impact its performance related to corrosion resistance and its tendency to blistering. Recent studies have highlighted the impact of the distribution of the pretreatment layer on the tendency to blistering and were able to partially link it to the presence of the native aluminum oxide film at the surface [12][13][14][15][16][17]. Furthermore, studies have shown, that in the case of phosphate-based and chromate-based conversion layer, the presence of the native aluminum oxide film at the surface could delay the formation of the conversion layer and thus reduce its thickness [2,4,16,18].…”

Crystal Structure and Properties of Zinc Phosphate Layers on Aluminum and Steel Alloy Surfaces

“…This zinc phosphate layer is also intended to ensure proper adhesion of the applied paint layer [2]. On the other hand, phosphate coatings on the zinc surfaces, e.g., on the hot-dip galvanized or electrogalvanized zinc surface of the car body, must not only provide excellent corrosion resistance but also ensure good paintability and good adhesion of the paint layer [7][8][9][10]. During surface protection by phosphating, a phosphate layer consisting of crystals and/or mixed crystals containing iron, zinc, and manganese is formed on the metal surface, depending on the composition of the phosphating solution [6].…”

“…This study investigates the simultaneous phosphating of aluminum and steel alloy surfaces on the same technological line using nitrite (N) and nitroguanidine (NG) accelerators. Nitrite is the most used and most effective accelerator and is particularly beneficial for steel surfaces [1,8,13]. However, the disadvantage of these systems is that, usually, nitrite levels must be kept high, especially for spraying processes, thus polluting the effluent and producing toxic nitrous gases [4].…”