Corrosion Behavior of Commercial Aluminum Alloy Processed by Equal Channel Angular Pressing

A commercial aluminum alloy was subjected to severe plastic deformation through equal channel angular pressing (ECAP). The alloy contains a low volume fraction of α-AlFeSi located essentially at the grain boundaries. The corrosion behavior of the ECAP’ed alloy was investigated in NaCl solution using potentiodynamic polarization and immersion tests. The effects of scan rate and NaCl concentration on the alloy susceptibility to corrosion were also studied. The results obtained were compared with those of the nonpressed alloy. ECAP leads to an intensive grain refinement accompanied by an increased dislocation density. All electrochemical tests confirm that corrosion resistance of the alloy remarkably diminished with increasing the ECAP number of passes. This is presumably due to the breakdown of the α-AlFeSi after ECAP leading to higher number of galvanic cells and enhanced dissolution of the aluminum matrix. 1. Introduction It is now well known that severe plastic deformation (SPD) leads to enhanced grain refinement to the submicrometer (100–1000？nm) or nanometer (<100？nm) levels. The intensive grain refinement is responsible for the enhancement of physical and mechanical properties of the processed materials, such as high strength and ductility. SPD techniques include, among others, torsion under high pressure [1], accumulative roll bonding (ARB) [2], and equal channel angular pressing (ECAP) [3, 4]. The latter procedure, introduced almost 30 years ago to achieve enhanced plastic strains, is especially attractive for several near superplastic applications. Since the cross-section of the sample remains unchanged during ECAP, repetitive pressings on the same sample are possible to achieve the required strains and to invoke different slip systems by rotating differently the sample between consecutive passes [4]. Thus, the microstructure obtained after ECAP depends on the introduced strains and whether and how the sample is rotated between two successive passes. In the early stages of pressing, reported results in the literature showed that the microstructure was reasonably homogeneous and consisted of parallel bands of subgrains. For further pressings, these subgrains evolved into an array of refined grains separated by high angle boundaries [5]. As a result of the grain refinement, a significant improvement of the mechanical properties was observed after ECAP [6]. In addition, ECAP process alters the bulk of the material leading to changes in material flow, residual stress, texture, size and distribution of a second phase if any exists in the material, and