Pitting Corrosion Resistance of Anodized Aluminum Alloy Processed by Severe Plastic Deformation

Abstract

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.

Effect of Annealing on the Pitting Corrosion Resistance of Anodized Aluminum-Magnesium Alloy Processed by Severe Plastic Deformation

“…10,11) As can be seen from Fig. 8, the compressive stress in anodic oxide films of Al-Mg alloy was larger with ECAP than without.…”

“…The pitting corrosion of Al is reported to originate around these precipitates not oxidized. 10,11) It is clear that the pitting corrosion originates around the precipitates and generates cracks through the pitting area in the anodic oxide films, as shown in Fig. 6.…”

“…[3][4][5][6][7] Authors previously reported that the pitting corrosion resistance of Al and Al-Mg alloy was improved by ECAP, but the corrosion resistance of anodized Al-Mg alloy was worse with ECAP than without. [8][9][10][11] In the case of anodized Al-Mg alloy, cracks occurred in the anodic oxide films during initial corrosion and the cracks were larger with ECAP than in its absence, suggesting that the internal stress generated in Al-Mg alloy as a result of severe plastic deformation has harmful effect on the pitting corrosion resistance of anodized Al-Mg alloy. However, no mechanism has been reported that explains the reduction in pitting corrosion resistance of anodized Al-Mg alloy.…”

Pitting Corrosion Resistance of Anodized Aluminum-Copper Alloy Processed by Severe Plastic Deformation

“…On the other hand, authors have already reported that the pitting corrosion resistance of Al-Mg alloy after anodization was worse with ECAP than without. 11,12) This suggests that the effect of ECAP on the pitting corrosion resistance of anodized Al alloys changes according to the kind of alloying elements. The time to pitting corrosion of anodized Al-Cu alloy increased with increased anodizing current density.…”

“…Authors reported previously that the pitting corrosion resistance of Al and Al-Mg alloy was improved by ECAP, but the corrosion resistance of anodized Al-Mg alloy was worse with ECAP than without. [9][10][11][12] The pitting corrosion resistance of anodized Al alloys depends on the alloying elements, and the effect of ECAP on the pitting corrosion resistance also seems to change according to the kind of alloying elements. In this study, copper was selected as the alloying element, and the effect of ECAP on the pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP was investigated using electrochemical techniques.…”