Mechanisms of the coupled phenomena during the resistance spot welding are examined using coupled finite element analyses. During the welding process, the electric current conducting just below the electrodes moves outward between the high temperature region and the high contact resistance region accompanied by the growth of contact surface, high Joule heat region and high temperature region. The nugget area is formed and grows under such complicated coupled effect among electric, thermal and contact phenomena. When electric current applied is higher, the conducting current moves outward together with the high temperature region, which leads to larger heat generation on account of the higher electric resistivity in the base metal region, and then leads to larger nugget area. When the electrode force applied is larger, the temperature along the interface becomes lower because of the reduction of current density.
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