Effect of Equal-Channel Angular Pressing on Pitting Corrosion of Pure Aluminum

Abstract

The effect of equal-channel angular pressing (ECAP) on the pitting corrosion of pure Al was investigated using electrochemical techniques in solutions containing 0.1 m mol·dm −3 of Na 2 SO 4 and 8.46 mol·dm −3 of NaCl (300 ppm Cl − ) and followed by surface analysis. The potential for pitting corrosion of pure Al was clearly shifted in the noble direction by the ECAP process indicating that this process improves resistance to pitting corrosion. The time dependence of corrosion potential and the anodic potential at 1 A·m −2 revealed that the rate of formation of Al oxide films increased due to a decrease in the grain size of the Al after ECAP. Since there exists a negligible amount of impurity precipitates in pure Al, the improvement in pitting corrosion resistance of pure Al by ECAP appears to be attributable to an increase in the rate of formation of Al oxide films.

Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview

“…A) As the most simple structure, a various kind of pure metals of high and commercial purity such as aluminum, [87][88][89][90][91][92][93][94] copper, 6,37,[95][96][97][98][99][100][101][102][103][104][105][106] iron, 76,107) titanium, [108][109][110][111][112][113][114] magnesium, 34,72,[115][116][117] have been processed by SPD for corrosion studies. In this simple system, grain size or grain boundary density impacts the corrosion resistance as a primary metallurgical variable with very few other metallurgical changes involved.…”

“…Corrosion behavior has been investigated on UFG materials fabricated mainly by processing of SPD such as ECAP, ARB, HPT for aluminum and its alloy, [87][88][89][90][91][92][93]120,121,143,[150][151][152][153]156,[158][159][160][161][162][163][164][165][166][167][168][169][170][171] magnesium and its alloy, 34,72,[115][116][117]122,123,154,157,[172][173][174][175][176][177][178][179] copper and its alloy, 6,[96][97][98]…”

“…Majority of papers report that the UFG materials in passive media exhibit higher corrosion resistance following the Ralston s rule 44) , its superiority manifests itself by breakdown potential rather than passive current. However, there is some inconsistency among the literature, even for pure aluminum, reporting favorable effect of UFG, 89,92,171) marginal change, 158) unfavorable effect. 87,93,158,162) The favorable effect is attributed to the readily formation of oxide lm because atoms at grain boundaries site are reactive to chemical species in the environment.…”

“…87,93,158,162) The favorable effect is attributed to the readily formation of oxide lm because atoms at grain boundaries site are reactive to chemical species in the environment. 89,92,171) One possible explanation for this contradictory results is the purity; lower purity may results in the degradation of corrosion properties by SPD. Eizadjouet et al 93) attributed lower corrosion resistance to re nement of Al 3 Fe, Al 6 Fe intermetallics and related defective passive lms.…”

Microhardness and corrosion properties of hypoeutectic Al–7Si alloy processed by high-pressure torsion

“…There have been a number of studies on the effect of grain refinement on the corrosion performance of aluminum alloys [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34], but there is little consensus whether SPD techniques can improve the corrosion performance of aluminum alloys. Moreover, most interest has been focused on the use of equal-channel angular pressing (ECAP) for studies of the effect of grain refinement on the corrosion resistance of pure Al [18][19][20][21][22][23] and its alloys AA2024 [24][25][26], AA6082 [27], Al-Si alloys [28][29][30]. For example, Akiyama et al [18] reported that ECAP resulted in deterioration of corrosion resistance of pure Al in a neutral buffer solution containing 0.002 mol L À1 chloride ion, while other research groups [19][20][21] observed that grain refinement with ECAP improved corrosion resistance of pure Al in chloride-containing solutions.…”