Room Temperature Washing-Free Composite Phosphating Coating Modified with Barium Salt

Room-temperature fast phosphating of steel was conducted in a barium salt-modified composite phosphating solution consisting of phosphate, zinc oxide, calcium nitrate, barium nitrate and ammonium molybdate to generate color washing-free phosphating coating after drying in air for more than 3 h. The morphology and composition of the composite phosphating coating were analyzed by means of scanning electron microscopy and energy dispersive spectrometry. Results show that the washing-free phosphating coating consists of the phosphates of Fe2+, Zn2+, Ca2+, Ni2+, Mn2+ and Ba2+, and a small amount of molybdates. The phosphating coating was continuous and compact with a crystalline size of less than 2 μm and weight of 1.5 g/m2, and only experienced slight corrosion after being immersed in 3% NaCl solution for 2 h. After being coated with iron red epoxy resin lacquer, the adhesion of the phosphating coating reached first grade.