Alternately direct resistance spot welding of al-to-al, al-to-steel, and steel-t0-steel with welding electrode having oxide-disrupting structural features

A method of resistance spot welding workpiece stack-ups of different combinations of metal workpieces with a single weld gun using the same set of welding electrodes, the method comprising:

• providing a weld gun that carries a set of opposed welding electrodes, each of the opposed welding electrodes having a weld face that comprises an original shape and oxide-disrupting structural features, wherein the oxide-disrupting structural features are in the form of a series of upstanding circular ridges, a series of recessed circular grooves, or a microtexture;
• forming a set of aluminum-to-steel spot welds, each of the aluminum-to-steel spot welds comprising a weld joint contained within an aluminum workpiece that weld bonds the aluminum workpiece to an adjacent steel workpiece;
• and
• forming at least one of (1) a set of aluminum-to-aluminum spot welds before forming the set of aluminum-to-steel spot welds or (2) forming a set of steel-to-steel spot welds after forming the set of aluminum-to-steel spot welds, each of the aluminum-to-aluminum spot welds comprising an aluminum nugget that fusion welds two or more aluminum workpieces together, and each of the set of steel-to-steel spot welds comprising a steel nugget that fusion welds two or more steel workpieces together.