Friction stir welding of electrolytic tough pitch copper plates was performed using a conventional CNC milling machine. A microstructural analysis was performed using optical and scanning electron microscopes and the mechanical properties were assessed. It is observed that the processing temperature, and thus welding parameters, is critical to obtain a sound joint. The characteristic weld nugget found in the friction stir welding of other metals was not observed in this material. Dynamic recrystallization was detected in the welding zone and the grain size varied depending on the relative location of the region examined with respect to the tool location. The tensile strength of the copper weld was determined to be 90% of the tensile strength of the base plate. Both the tensile and hardness results are correlated with the weld microstructure. The corrosion resistance of the weld was assessed in connection with the grain distribution, using Electrochemical Impedance Techniques; no significant differences were observed in the corrosion behavior the weld compare to the unaffected metal. Copyright © 2006 ASM International®.