Stress corrosion cracking characteristics of aluminum alloy specimens with different thicknesses

In view of the influence of specimen thickness on the critical stress corrosion intensity of aluminum alloys materials and how to evaluate stress corrosion sensitivity of thick wall components in practical engineering application, the pre-crack DCB (double cantilever beam) specimens with 40 mm in thickness were used to represent the thick wall of parts in practical engineering application, and 26mm thick specimens specified in GB 15970.6-2007 standard were used for studying the stress corrosion fracture characteristics of 2024-T351. The results showed that the critical stress corrosion intensity K_ISCC of 40 mm thick DCB specimen was bigger than that of 26 mm thick specimen. The influence of the thickness of DCB specimen with S-L direction was not obvious and the difference was about 4%. For S-T direction, the influence of the thickness of sample was significant and the difference was about 24%. Fibrous corrosion products were discovered at stress corrosion fracture surface of DCB specimen. By energy disperse spectroscopy (EDS) and X-ray diffraction (XRD) analysis, the fibrous corrosion products were aluminum hydroxide. Fibrous corrosion products reduced the accumulation of corrosion products at the crack tip of DCB specimen, so as to reduce the influence of corrosion products wedge effect on stress corrosion cracking threshold value K_ISCC and improve the stress corrosion resistance of materials. Fibrous corrosion products on the stress corrosion fracture surface of 40 mm thick DCB specimen were significantly more than those of 26 mm thick DCB specimen's. It was one of the reasons that the stress corrosion cracking threshold value of 40 mm thick specimen was greater than that of 26 mm thick specimen. In the process of stress corrosion cracking, the crack tip of DCB specimen got acidic and the body solution got alkaline, owing to the anode reaction at the crack tip of DCB specimen and forming small anode and big cathode system with the body solution. In the process of stress corrosion cracking, pH value at the crack tip was about 3.0 for 40 mm thick specimen and 3.6 for 26 mm thick specimen. Acidification at the crack tip of 40 mm thick DCB specimen was more serious.