The Effect of Velocity on Galvanic Corrosion on AI Alloys^★

The effect of relative velocity metal/electrolyte on galvanic corrosion has been studied for Al 6061 coupled to Cu, 4340 steel, Type 304 stainless steel, Ti-6Al-4V, and Zn in 3.5% NaCl and in substitute ocean water (ASTM D1141). The electrodes were in the form of cylinders, which were mounted on an electrode holder previously described in the literature. Experiments were conducted in stagnant solutions and at velocities up to 2.5 m/s. For some galvanic couples in 3.5% NaCl, a linear relationship between the galvanic current and the square root of velocity is observed. For other couples in NaCl, and for all couples in substitute ocean water, a more complicated relationship is determined. Anodic and cathodic polarization curves have been measured as a function of velocity. From these curves, the limiting current density (cd) for oxygen reduction has been determined, and a linear relationship with the square root of velocity has been observed. A theoretical analysis of the velocity dependence of the corrosion cd and galvanic cd is presented which is based on the experimental polarization curves.