Effects of Forming Conditions on Exfoliation of Galvannealed Steel Sheet

The exfoliation behavior of heavy coat galvannealed steel sheet was investigated by an actual press forming of the front fender. With the increase in coating weight from 45g/m² to 60g/m², the exfoliation changed from powdery to flakey (flaking) in the bead-slided portion. The flaking phenomenon was reproduced experimentally due to sliding at high speed press forming under high normal pressure (high ironing ratio, small bead radius, and high bead height). Flaking resistance of Fe-Zn electro-plated galvannealed steel sheet was also stuied. The effect of Fe-Zn electro-plating changed depending on the various forming mode.