In this work, we evaluated and compared the intergranular corrosion on AZ31B magnesium alloy welded by friction stir processes with tungsten arc and gas welding. The electrochemical impedance spectroscopy technique was used to evaluate and compare the corrosion behavior of both weldings. In addition, microstructural analysis of the grain boundaries was performed by microscopy. The results of this study show an increased corrosion resistance of the specimens obtained by the friction stir process.