This present study focused on the effect of aluminum nitrate pre-treatment on the properties of the subsequent silica coating, including the adhesion and high temperature oxidation resistance of the coating. Aluminum nitrate pre-treatment was employed to precipitate aluminum oxide and hydroxide on the substrate in order to provide a homogenous surface and improve the oxidation resistance. The silica coating was synthesized by a sol-gel method from tetraethoxysilane (TEOS) and 3-glicidoxipropyl-trimetoxisilano (GPTMS) precursor solution. The silica coating was applied via dip coating on a commercial hot-dip galvanized steel received from the China Steel Corporation, Kaohsiung, Taiwan, and was subsequently cured to confer high temperature oxidation resistance. The high temperature oxidation resistance was evaluated using the thermal gravimetric analysis (TGA, TA Q50) and the microstructural evolution during austenitization. Experimental results showed that the silica coating with pre-treatment had better high temperature oxidation resistance and hindered the liquid phase evaporation. Therefore, it is evident that the aluminum nitrate pre-treatment had positive effects to suppress high temperature oxidation. The Auger spectroscopy analysis further revealed that the surface of the hot-dip Zn coating became chemically homogeneous after the aluminum nitrate pre-treatment, signifying the necessity of a homogeneous aluminum hydroxide surface layer to enhance the adhesion and oxidation resistance of the silica coating on hot-dip galvanized steel during austenitization.
Keywords: Press hardening steel; Hot-dip galvanized steel; Silanes; Sol-Gel; Pre-treatment