Improving Corrosion Resistance of Al through Sever Plastic Deformation 2-under Accelerated Condition

        THE CORROSION resistance of Aluminum (Al) in 3.5% NaCl …….was improved after surface mechanical attrition treatment (SMAT). Cyclic potentiodynamic polarization (CPP) measurements have shown hysteresis’s loop area owing to localized attack. Surface examinations using scanning electron microscopy (SEM), electron dispersive X-ray (EDX), X-ray diffraction (XRD) and grazing induced X-ray diffraction (GIXRD) have been used to investigate changes of composition on the surface at different depths. The result of polarization shows that as increasing the time of annealing before 10 min SMAT the surface of Al becomes more resistance and behaves similar to that of adding cathodic inhibitor. The study was carried out also for the annealed samples after different time of SMAT 0, 5, 10, 15, 20 and 25 min. proved that the corrosion resistance was improved with increasing the time till 15 min treatment and decreased again after that. CPP experiments at all the time except at 15 min SMAT recorded the formation of different steps at different potential after the corrosion potential. The steps are similar to that recorded due to formation of protective film and the break down due to pitting corrosion. GIXRD proved that the appearance of these steps is due to the formation of different metallic and intermetallic solid solution phases which have different corrosion potential. On the other hand the more corrosion resistance of 15 min SMAT was attributed to the formation of the most anodic phase of Al₃₉ Cu₄₇. The dissolution of the treated SMAT Al in 3.5 % NaCl are localized attack and mainly intergalvanic corrosion where its rate depends on the defence between the corrosion potential of the phases recorded and the Al substrate.