The role of hydrogen in the corrosion-induced reduction of plane-stress fracture toughness and strain-induced intergranular cracking of AA2024

Abstract

The role of diffusible hydrogen in the embrittlement of AA2024 after short-term exposure in the standard exfoliation corrosion (EXCO) test solution (ASTM G34) was investigated. Slow strain rate KR-curves were established – utilizing the unloading compliance method of the ASTM E561 Standard – on 3.2 mm thick compact tension (C(T)) specimens for the following four (4) sets of samples: (i) as-received (unexposed), (ii) 2 h EXCO exposed, (iii) unexposed and heat-treated, and (iv) 2 h EXCO exposed and heat-treated samples of AA2024. A significant degradation (≈ 12.0 ± 1.8 %) was observed in the effective slow strain rate KC toughness after short-term exposure of the AA2024-T3 specimens to the EXCO-solution. Post-exposure heat-treatments appear to have restored the plane-stress fracture toughness to its original values. The formation of secondary and primary intergranular cracks in the plastic zone of the C(T) samples were studied using SEM. The presence of intergranular secondary surface cracks in the plastic zones of the C(T) samples was, however, not altered by the heat treatment, and did not appear to influence the fracture toughness results. Thermal desorption mass spectroscopy was exploited to evaluate the extent of hydrogen absorption due to the corrosive exposure, and the effect of the subsequent heat treatment in removing it.