Development of nano TiO2-incorporated phosphate coatings on hot dip zinc surface for good paintability and corrosion resistance

Phosphating is one of the most important chemical conversion processes for the purpose of corrosion protection and primer for painting. In the present work, nano TiO2 incorporated phosphate coating was developed on hot dip galvanized zinc surface for achieving good paintability and corrosion resistance. Based on the results from preliminary studies, the amount of nano TiO2 incorporated into the phosphating bath was optimized as 0.1 g. TiO2 incorporation effectively reduced the extent of zinc dissolution during phosphating and activated the process to achieve the expected coating weight faster. Also it yielded coating with greater thickness than the normal phosphate coating. The TiO2 incorporation resulted in a well crystallized phosphate coating with large crystal size and greater surface coverage. Results from the electrochemical analysis revealed the better barrier protection characteristics and enhanced corrosion resistance of TiO2 incorporated phosphate coatings over the normal phosphate coatings.