The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al and Al-Mg alloy was investigated by means of polarization curves in solutions containing 300 ppm of Cl À and by surface analysis. The potentials for pitting corrosion of Al and Al-Mg alloy were clearly shifted in the noble direction by the ECAP process, indicating that this process improves resistance to pitting corrosion. SEM observations revealed that pitting corrosion occurred near impurity precipitates and that the size of the impurity precipitated decreased as a result of the ECAP process. The time-dependence of corrosion potential and the polarization resistance determined using the AC impedance technique suggest that the ECAP process increases the rate of formation of Al oxide films. The improvement in pitting corrosion resistance of Al and AlMg alloy by ECAP appears to be attributable to a decrease in the size of impurity precipitates and an increase in the rate of formation of Al oxide films.

The effect of equal channel angular pressing (ECAP) on the pitting corrosion resistance of anodized Al and Al Mg alloy was investigated by electrochemical techniques in a solution containing 0.25 mol/L of AlCl 3 and by surface analysis. The time required before initiating pitting corrosion of anodized Al was longer with ECAP than without, indicating improvement in the pitting corrosion resistance by application of ECAP. However, in anodized Al Mg alloy, the pitting corrosion occurred earlier with ECAP than without, showing that the corrosion resistance was worse with ECAP than without. SEM and EPMA observation revealed that pitting corrosion of anodized Al occurred around the impurity precipitates and that the size of the impurity precipitate decreased as a result of the ECAP. The improvement in pitting corrosion resistance of anodized Al by ECAP appears to be attributable to a decrease in the size of impurity precipitates. On the other hand, in anodized Al Mg alloy, cracks occurred in the anodic oxide films during initial corrosion and the cracks were larger with ECAP than without. It is assumed that the pitting corrosion was promoted by the cracks resulted from ECAP.

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The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L of AlCl 3 and also by surface analysis. The time required before initiating pitting corrosion of anodized Al-Cu alloy was longer with ECAP than without, indicating improvement in the pitting corrosion resistance by application of ECAP. Second phase precipitates were present in Al-Cu alloy matrix and the size of these precipitates was greatly decreased by application of ECAP. The precipitates composed of Si and Al-Cu-Si-Fe-Mn were not oxidized during anodization, and the anodic oxide film were absent at the boundary between the normal oxide films and these impurity precipitates. The pitting corrosion of anodized Al-Cu alloy occurred preferentially around these precipitates, the improvement of pitting corrosion resistance of anodized Al-Cu alloy by ECAP appears to be attributable to a decrease in the size of precipitates, which act as origins of pitting corrosion.

The effect of annealing on the pitting corrosion resistance of anodized Al-Mg alloy processed by equal-channel angular pressing (ECAP) was investigated by electrochemical techniques in a solution containing 0.2 molÁL À1 of AlCl 3 and also by surface analysis. The degree of internal stress generated in anodic oxide films during anodization was evaluated with a strain gauge. The ECAP decreased the pitting corrosion resistance of anodized Al-Mg alloy. However, the pitting corrosion resistance was improved by annealing after the ECAP. The internal stress present in the anodic oxide films was compressive, and the stress was higher in the alloys with ECAP than without. The compressive internal stress gradually decreased with increasing annealing temperature. Cracks occurred in the anodic oxide film on Al-Mg alloy during initial corrosion. The ECAP produces high internal stresses in the Al-Mg alloy; the stresses remain in the anodic oxide films, increasing the likelihood of cracks. It is assumed that the pitting corrosion is promoted by these cracks as a result of the higher internal stress resulting from the ECAP. The improvement in the pitting corrosion resistance of anodized Al-Mg alloy by annealing appears to be attributable to a decrease in the internal stresses in anodic oxide films.