Incorporation of boron nitride nanosheets in zinc phosphate coatings on mild steel to enhance corrosion resistance

Abstract To enhance corrosion resistance of zinc phosphate coatings on mild steel, boron nitride nanosheets (BNs) were introduced into zinc phosphating bath. The effects of BNs on the phase composition, surface morphology and corrosion resistance of phosphate coatings were investigated by varying the concentration of BNs (0.15–0.60 g/L) in the phosphating bath. Results show that the presence of BNs could effectively reduce the crystal sizes of phosphate crystals and thus make BN-incorporated phosphate coatings denser and finer than pure phosphate coatings. Moreover, BN-introduced phosphating bath yields heavier phosphate coatings (25.10 g·m −2 ). In the electrochemical corrosion measurements, BN-incorporated phosphate coatings display the corrosion current of 3.21 × 10 −6 A/cm 2 , which is one order of magnitude lower than the ones without BNs. Moreover, the time against corrosion of copper sulfate dropping prolongs to 328 s for BN-incorporated samples, which is an increase of 182.75% compared with pure ones.