Method and apparatus for resistance spot welding overlapping steel workpieces

A method of resistance spot welding overlapping steel workpieces, the method comprising:

• providing a workpiece stack-up comprising a first steel workpiece and a second steel workpiece that overlap each other at a weld site, the first steel workpiece having an exterior outer surface that provides a first side of the workpiece stack up and the second steel workpiece having an exterior outer surface that provides a second side of the workpiece stack-up, wherein at least one of the first and second steel workpieces comprises an advanced high-strength steel substrate having an ultimate tensile strength of greater than 550 MPa and a microstructure that includes greater than 5 vol % austenite, martensite, or bainite at ambient temperature;
• positioning the workpiece stack-up between a pair of opposed first and second welding electrodes such that a weld face of the first welding electrode faces toward the first side of the workpiece stack-up and a weld face of the second welding electrode faces toward the second side of the workpiece stack-up, and wherein a cover is disposed between at least one of the first steel workpiece and the first welding electrode or the second steel workpiece and the second welding electrode at the weld site;
• clamping the workpiece stack-up between the first and second welding electrodes at the weld site such that at least one of the weld faces of the first and second welding electrodes presses against the cover;
• and
• welding the first and second steel workpieces together by passing an electrical current between the first and second welding electrodes at the weld site,
• wherein the cover comprises an iron alloy having an ultimate tensile strength less than that of the advanced high-strength steel substrate.