Enhanced forming properties of galvannealed steel sheet by polymanganese phosphate coating

Polymanganese phosphate coating is obtained on galvannealed (GA) steel surface by dipping process. Coating weight of 1.1 g/m2 is found to give dense with uniform crystallites of size 1–2 μm. Energy Dispersive X-ray Spectroscopy and X-ray Diffraction results show that the coating composes of manganese phosphate hydrate and rockbridgeite. The coefficient of the friction of polymanganese coated galvannealed steel sheet is reduced significantly from 0.22 to 0.11 on the die. Manganese phosphate in the coating behaves as an anti-sticking base, thereby the contact zone is found to be smooth. Further, the treated sheet removes only 5.9 mg of Fe powder in the form of flakes as compared to the untreated sheet producing 12 mg Fe powder from its surface.