Resistance Seam Weldability of Polymer-Coated Steel Sheet

Methanol represents one of the most attractive alternative fuels intended to replace gasoline, but it is corrosive to the terne-coated steel sheet traditionally used for automobile fuel components. Application of a methanol-resistant polymer coating on a steel substrate was found to be a viable solution for methanol-resistant fuel tanks. One-sided electrogalvanized sheet was coated on the bare side with a nonconductive and adhesive thermoplastic. The present work studied the weldability of this sheet with the thermoplastic at the faying interface. A systematic parametric study was performed. Welds were evaluated using a set of criteria based on the joint integrity and corrosion resistance. It was found that the coating melted and resolidified in a continuous film adjacent to the welds. The resistance seam-welding operational envelopes were shifted toward lower welding travel speeds and welding currents. It was concluded that the polymer-coated steel sheet can be welded without significant changes in welding equipment and parameters presently used in manufacturing fuel tanks.