EIS was utilized as a novel approach to study the role of mechanical and electrochemical processes in flow accelerated pitting corrosion behaviour of AA5083-H321 aluminum-magnesium alloy in 3.5% NaCl solution. This alloy is a suitable material for manufacturing of high speed boats, submarines, desalination systems etc. Impedance spectra were obtained during 24 h of exposure of the samples to the test solution at different rotation speeds. The surface and cross section of the samples were studied by scanning electron microscopy (SEM) and EDAX analysis. The results indicated that increasing the rotation speed causes the depth of pits to increase. By further increasing the rotation speed to 5 and 7 m s(-1), the flow condition causes the passive layer inside the pits to breakdown. Simultaneously, the thickness of the passive layer on the areas other than the pits becomes thinner. Shear stresses at 10 m s(-1) are so severe that the passive layer on the entire surface breaks down and leads to micropitting corrosion.