Effect of ultrasonic treatment on the morphology and corrosion resistance of zinc-manganese phosphate coatings on 16Mn steel in 3.5 % sodium chloride

Different zinc-manganese phosphate coatings are prepared on the surface of 16Mn steel which are commonly used as construction structure materials. Ultrasonic treatment has been introduced in the process of phosphating to enhance the corrosion resistance of different zinc-manganese coatings. The experimental results indicate that ultrasonic has a certain impact on the surface morphology, thickness, and corrosion resistance of zinc-manganese phosphate coating, but it has no significant effect on the composition of zinc-manganese phosphate coating. The proper ultrasonic power applied promotes the formation of a zinc-manganese phosphate coating with a compact surface and large thickness which can effectively block the penetration of corrosive media and enhance the corrosion resistance. The zinc-manganese phosphate coating prepared using an ultrasonic power of 135 W demonstrates the best surface density with a thickness of 12.2 & mu;m, and its anti-dripping time, charge transfer resistance and low-frequency impedance modulus reach 236 s, 5696 51 cm2 and 4625 51 cm2, respectively. In comparison to the zinc-manganese phosphate coating obtained without ultrasonic, the zinc-manganese phosphate coating prepared with ultrasonic exhibits excellent corrosion resistance and can provide ideal surface protection for 16Mn steel as construction structure materials.