Improvement of pitting corrosion resistance for Al-Cu alloy in sodium chloride solution through equal-channel angular pressing

Significant corrosion resistance improvement was achieved in solid-solution treated (T4) Al-Cu alloy after severe grain refinement through equal-channel angular pressing. The bulk ultrafine-grained Al-Cu alloy with grain sizes of 200-300 nm has higher pitting potential (elevated by about 34 mV, SCE) and lower corrosion current density (decreased by about 3.88 µA/cm2) in polarization tests than the as-T4 alloy, and increased polarization resistance (increased by about 5.7 kΩ·cm2) in electrochemical impendence spectrum tests, along with alleviated corrosion damage in immersion tests. Two factors responds to the improved corrosion resistance of the alloy: the first is the refinement of residual θ-phase (Al2Cu) particles leading to the lower micro-galvanic currents and reduced susceptibilities to pitting corrosion, the second is the mass of strain-induced crystalline defects providing more nucleation sites for the formation of more volume fractions of stable oxide film.