Effect of Paint Film Factors on Press Forming of Zinc-rich Primer Painted Steel Sheet

A zinc-rich primer painted steel sheet for automobile body has much zinc powder in paint film for the purpose of doing spot welding. A paint film which has a large quantity of pigment is brittle and susceptible to flaking by press forming, and its corrosion resistance becomes poor. Some paint film factors influencing its flaking by press forming were studied. (1) By the addition of lubricant (ex. MoS2) to paint film, the flaking of the paint film is reduced. The effect of the lubricant addition is due to the reduction of the friction coefficient of paint film. As an other effect the lubricant is coated on the die, and good lubrication appears.(2) Generally, zinc powder content of zinc-rich primer paint film is about 90 wt%. By decreasing zinc powder content of paint film, the flaking of paint film is reduced. As the paint film becomes thicker, the shear stress on it decreases and flaking of the paint film is reduced.(3) The flaking of paint film on electroplated Ni-Zn alloy steel sheet is less than that on cold rolled one.