Study on the Corrosion Behavior and Mechanism of 6061 Aluminum Alloy under Alternating Current Interference in 3.5% NaCl Solution

The effect of alternating current (AC) on the corrosion behavior of 6061 aluminum alloy in 3.5% NaCl solution was studied by electrochemical measurements, immersion test and surface morphology analysis. Imposed AC increases the number of defects inside the passive film and reduces its compactness and integrity. Even at low iAC (30 A/m2), the anode branch of the polarization curve evolves from passivation state to activation state. Under the application of AC, the increase of corrosion rate and pitting depth reflects the corrosion form evolution of 6061 alloy from slight localized corrosion to complex corrosion morphology (including intergranular corrosion, exfoliation corrosion and a large number of different size pits). This is due to that AC increases the adsorption and mobility of ions, and generates the ion and atom of hydrogen. Moreover, AC promotes the micro-galvanic corrosion between the alloy matrix and the precipitated phase of AlFeSi, which leads to the occurrence of dense pits. In addition, under AC application, the AlFeSi phase itself dissolves rapidly, which is attributed to the selective dissolution of Al.