In this work, we present the decreased susceptibility to intergranular corrosion in AZ31 magnesium alloys welded by friction agitation process, varying the rotation and advance speed. To induce the corrosion effect was used as electrolyte a solution of 30g of NaCl and 10 ml of concentrated HCl, monitoring of degradation analysis was performed using electrochemical impedance spectroscopy and potentiodynamic polarization curves Tafel. Moreover, microstructural analyzes were performed of the grain boundaries by means of metallographic microscope and scanning electron microscope. It was found that a higher relationship among forward speed / rotation speed produces a weld bead with improved resistance to intergranular corrosion, possibly associated to a larger grain size in the stirred zone, in turn related to increased heat input by friction process.