The Effects of Coating Composition, Substrate, and Welding Machine on the Resistance Spot Welding Behavior of Hot-Dip Galvanized and Galvannealed Sheet Steels

This joint research study by Bethlehem Steel Corporation and the U. S. Steel Group of the USX Corporation reveals that several significant factors affect the welding performance (electrode life) of hot-dip galvanized and galvannealed sheet steels. The statistical analyses of the electrode life data reveal that coating aluminum content affects electrode wear behavior of both the hot-dip galvanized and the galvannealed coatings. Higher levels of aluminum content cause more rapid electrode wear and shorten electrode life. Iron content in the galvannealed coatings seems to have some positive effect on increasing electrode life, but its effect is not nearly as significant as the negative effect of aluminum content. As the Fe/Al coating content ratio of galvannealed coatings increases, electrode life increases. Substrate type also affects electrode life, with the IF grade consistently producing shorter electrode lives. This behavior is related to the lower bulk resistance (lower resistivity) of IF steels and the higher welding currents required to weld them. The welding machines of both laboratories were also noted to have a significant effect on electrode life, with Bethlehem's machine generally producing longer electrode lives.