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 mu A/cm(2)) in polarization tests than the as-T4 alloy, and increased polarization resistance (increased by about 5.7 k Omega.cm(2)) 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 theta-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.