Electrode degradation in resistance spot welding of magnesium alloy

Abstract

Mechanism of electrode degradation in resistance spot welding (RSW) of magnesium alloy has been investigated using scanning electron microscopy (SEM) and energy-dispersive spectrum (EDS). The results show that electrode degradation experienced mainly four basic steps (i.e. magnesium alloy pickup, electrode alloying with magnesium, electrode tip face pitting, and cavitation). Magnesium alloy pickup began from the first weld as tiny drops of molten magnesium alloy were transferred from the sheet surface to the electrode tip face. A complex alloy layer (Cu2Mg and CuMg2) was formed by the molten magnesium alloy reacting with the electrode. Electrode pitting occurred by brittle fracture of alloyed region formed on the electrode tip face resulting in material removal from the electrode tip face. Once the electrode pitting started, large cavities formed by combining smaller pits. Therefore, it is favorable to periodic cleaning of the electrode tip face for extending electrode life and obtaining well appearance of joint surface. © 2009 ISIJ.