120

FIGURE 9.5 Variation of pitting density and maximum depth of attack with exposure time during EXCO test.

throughout the entire exposure period of 90 days. It should be noticed that the alternate immersion test resulted in a much higher final pitting density than the EXCO test. However, the pits were at the same time finer. The depth of attack showed a similar behavior to the exfoliation test in that it increased slowly in the beginning of exposure and proceeded faster with longer exposure. Alternate immersion resulted in a higher depth of attack than the EXCO test. Figure 9.8 shows a characteristic micrograph of a sectioned specimen. As in the EXCO test, a network of intergranular attack developed in areas adjacent to the corrosion pits. However, intergranular attack parallel to the rolling direction was not observed.

9.6.3.2 Tensile Behavior of Corroded Specimens

Reference Materials The tensile properties of all reference materials are summarized in Table 9.39. The drop of elongation to failure and energy density obtained on alloy 2024-T3 following anodization coating and sealing is significant; coated 2024 material is referred to as "ref. 2." Investigations on this latter material were limited to the L direction.

FIGURE 9.6 Micrographs of sectioned specimens exposed to the EXCO test for 96 h: (a) network intergranular cracks and (b) exfoliation crack.

FIGURE 9.6 Micrographs of sectioned specimens exposed to the EXCO test for 96 h: (a) network intergranular cracks and (b) exfoliation crack.

TABLE 9.38 Depth of Attack after 48-h Exposure to Exfoliation Corrosion Solution

Alloy Depth of Attack

TABLE 9.38 Depth of Attack after 48-h Exposure to Exfoliation Corrosion Solution

Alloy Depth of Attack

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