Synchrotron-based holotomography and X-ray fluorescence study on the stress corrosion cracking behavior of the peak-aged 7075 aluminum alloy

The demand to reduce weight in the automobile industry necessitates an enhanced understanding of the stress corrosion cracking (SCC) mechanism of 7xxx series aluminum wrought alloys. Thus, the SCC susceptibility of 7075 aluminum wrought alloy wires, with respect to the heat treatment condition, solution annealed, peak-aged and overaged, was investigated via slow strain rate testing in 3.5 wt % sodium chloride solution. The SCC crack, initiated in a notched tensile specimen of the peak-aged condition, was investigated in detail by means of synchrotron-based high resolution holotomography and X-ray fluorescence as well as STEM in order to understand the correlation of microstructural features and cracking behavior. The local crack initiation and macroscopic crack propagation was found to be dependent on the stress fields, which were simulated by the finite element method. In the peak-aged condition, the SCC crack propagated microscopically along the grain boundaries leading to a brittle intergranular fracture. The SCC mechanism in the peak-aged condition was related to a combination of hydrogen embrittlement and an anodic-dissolution-induced notch effect that was attributed to a continuous seam of grain boundary (GB) precipitates. (C) 2019 Elsevier B.V. All rights reserved.