Effects of compressive stress on localized corrosion in AA2024-T3

The effect of compressive stress on intergranular corrosion (IGC) of AA2024-T3 was studied using a constant load and simultaneous electrochemical measurement. A specially designed electrochemical cell was used to compress a pillar-shaped sample and control the potential at a value that promoted IGC. The extent of IGC was assessed by metallurgical cross-sectional images. The effect of the compressive stress depended on the orientation of the stress relative to the elongated microstructure. Application of a compressive stress halfway to yield in the S or through-thickness direction significantly reduced the growth kinetics of IGC in the longitudinal direction, but did not eliminate it totally. The strain change during exposure also was used to quantify the change in radius of the cylindrical sample as a function of time during IGC growth. The effect of compression on reducing IGC was also assessed by the current density measured during potentiodynamic and potentiostatic polarization. The effects of residual compressive stress on IGC were studied using samples treated by low plastic burnishing (LPB), which produces a surface layer with high residual compressive stress. The results depended on the plane of the LPB treatment. A micro-capillary cell was used to measure corrosion behavior at different zones of the section of an LPB-treated sample. The breakdown potential was significantly higher in the zone with residual compressive stress than in the interior of the sample.