Abstract
Effects of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al-Cu (AA2024) alloy with and without anodization were investigated using surface analysis and polarization curves in solutions containing 300 ppm or 0.6 mol·dm−3 of Cl−. The pitting corrosion potential and corrosion rate of Al-Cu alloy revealed no effect of ECAP on the pitting corrosion resistance of Al-Cu. The Al-Cu alloy contained such precipitates as Al2Cu, Al2CuMn and Al-Cu-Si-Fe-Mn intermetallic compounds, around which pitting corrosion occurred. Actually, ECAP pulverized these precipitates to decrease their size, but it had no effect on the pitting corrosion resistance of Al-Cu alloy because pitting corrosion occurred even around small precipitates of Al2Cu. In contrast, the time to initiate pitting corrosion of Al-Cu alloy while maintaining a constant potential of 1.2 V was longer with ECAP than without, indicating that ECAP improved the pitting corrosion resistance. Although the precipitates of Al2Cu and Al2CuMn disappeared because of oxidation during anodization, Al-Cu-Si-Fe-Mn intermetallic compounds were present and formed defects in anodic oxide films. Pitting corrosion of the anodized Al-Cu alloy occurred around the Al-Cu-Si-Fe-Mn precipitates. The improved pitting corrosion resistance of anodized Al-Cu alloy by ECAP appears to be attributable to the decreased size of the precipitates that initiate pitting corrosion.
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