Effect of the number of ECAP pass time on the electrochemical properties of 1050 Al alloys

The effect of equal channel angular pressing (ECAP) pass number on the electrochemical properties of AA 1050 (UNS A91050) were investigated by electrochemical techniques (potentiodynamic polarization test, potentiostatic test, electrochemical impedance spectroscopy (EIS) measurement) and surface analyses (OM, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS)) in 0.1 M Na₂SO₄ solution containing 100 ppm chloride ions. The ECAPed specimens that have a various numbers of passes from N=1-5 were selected for electrochemical experiments in this study. The results of potentiodynamic test indicated that the breakdown potential increased with increasing the ECAP pass number. EIS measurements also showed that the corrosion resistance of the AA 1050 increased with increasing the ECAP pass number at the passivation and breakdown states. The results of surface analyses (SEM, EDS) showed that silicon-containing impurities were observed on the surface of the alloy. It was found that the size of these Si-containing impurities decreased with increasing the ECAP pass number. The Si-containing impurities induced the microgalvanic reaction (i) between the Al matrix and the Si-containing mixed oxide and (ii) between the Al matrix and the Si-containing impurities. Due to its ultrafine-grained microstructure, ECAPed AA 1050 had smaller Si-containing impurities, and reduced microgalvanic currents. Thus, in the case of ECAPed AA 1050, it has increasing corrosion resistance with increasing ECAP pass number because of its small cathodic impurities.