Galvannealed Sheet Steel with Fe-P Flash Electro-Coating for Exposed Panels of Automobiles

The Effects of Fe-P flash electro-coating on several properties of galvannealed sheet steel with coating of 60 g/m² were investigated to apply galvannealed sheet steel not only to inner panels but also to exposed panels. The allowable range of Fe content in galvannealed coating for anti-powdering property is from 7 wt% to 9.5 wt%. However, this range of Fe content gives higher coefficient of friction for the galvannealed sheet steel against die due to the existence of soft phase, ζ, at surface. The amount of Zn peeling off by flaking increases with the decrease in Fe content below 10 wt% in the case of no lubrication. Fe-P flash electro-coating on galvannealed sheet steel is effective to decrease the coefficient of friction and the amount of Zn peeling off by flaking, and does not influence the anti-powdering property. Fe-P coating also improves drastically the properties of phosphatability and anti-cratering in cathodic electrodeposition, which are generally very poor in galvannealed sheet steel. On these knowledge, the Fe-P flash electro-coated galvannealed sheet steel with the excellent coating adhesion, superior frictional property, phosphatability, anti-cratering and cosmetic corrosion resistance has been produced and successfully applied to the exposed panels of the automobiles.