Apparatus and methods for reducing corrosion of joining composite workpieces

A method, for joining a first workpiece and a second workpiece, comprising:

• positioning, near an upper surface of the first workpiece, a mandrel configured to be received through at least a portion of a rivet body,
• the rivet body comprising a rivet shank, having a diameter, and a rivet head comprising an upper surface and a lower surface, the lower surface of the rivet head becoming located in the positioning near the upper surface of the first workpiece, wherein the rivet body is at least partially composed of a non-conductive material that eliminates electrochemical pathways between the rivet body and at least one of the first and second workpieces and the rivet body;
• and
• the mandrel comprising a mandrel shaft and a mandrel cap that is positioned on a portion of the mandrel shaft in connection with the rivet shank, wherein the mandrel cap is composed of a cap material having a hardness greater than that of the first and the second workpieces, thereby allowing passage of the mandrel cap through the first and second workpieces;
• and
• applying, to the upper surface of the rivet head, a torque such that the mandrel cap generates frictional heat at the upper surface of the first workpiece, the frictional heat deforming the upper surface of the first workpiece and creating a cavity extending into the first workpiece from the upper surface of the first workpiece.