7N01铝合金应力腐蚀行为研究

7N01 aluminum alloy is a kind of aluminum alloy used in the structure of rail transport train body. It has been widely used because of its good workability and weldability. However, 7N01 aluminum alloy has inferior resistance to exfoliation corrosion and stress corrosion, which leads to many failure accidents. Therefore, it is necessary to understand the stress corrosion behavior of 7N01 aluminum alloy. For investigating the stress corrosion mechanism of 7N01 aluminum alloy is controlled by the mechanism of anodic dissolution (Al atoms converse to Al ion, leading to corrosion pits) or hydrogen-induced cracking (H atoms combine to H₂, leading to Hydrogen bubbling or crack). The effects of structure of 7N01 aluminum alloys on its stress corrosion mechanism were studied with electrochemical hydrogen charged and non-hydrogen charged T7 (Overaging, 475 ℃/1 h+120 ℃/96 h) and T4 (underaging, 475 ℃/1 h +25 ℃/15 d) samples. By means of transmission electron microscope (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), slow strain rate tension (SSRT) and electrochemical analysis, stress corrosion cracking (SCC) behavior of 7N01 aluminum alloy was studied. TEM and XRD results showed that there was no obvious precipitation at grain boundaries of 7N01-T4. A few coarse precipitates could be found in the grains. The PFZ width of 7N01-T7 was 38 nm, and there were a large number of dispersed precipitates in grains, mainly η(MgZn₂) phase; The electrochemical analysis results showed that corrosion rate of 7N01-T7 was higher than that of 7N01-T4, and that of LS (longtitudinal-short) surface was higher than that of ST (short-transverse) surface. SSRT results showed that at the strain rate of 6.67×10^-6 s^-1, T4 showed no obvious SCC behavior, while T7 had higher SCC susceptibility than T4. SCC susceptibility of ED (parallel to the extrusion direction) was equal to that of ND (normal to extrusion direction); SCC susceptibility consists of the susceptibility caused by corrosion, and the additional susceptibility caused by the interaction between stress and corrosion. The susceptibility caused by corrosion, I_corr could be characterized by the plasticity and strength loss of the specimens which preimmersed in 3.5% NaCl aqueous solution. The additional SCC susceptibility, I_c-σ, which could be caculated by the difference of I_SCC and I_corr, indiced of ED and ND of 7N01-T7 are 0.011 and 0.148, respectively. SSRT in 3.5% sodium chloride solution could make the material contain high content of hydrogen, which reduced pitting potential and increased corrosion current density, thus reducing the corrosion resistance of the material. The mechanical performance loss of ED-T7 and ND-T7 specimens caused by hydrogen in I_SCC was 84.7% and 66.7%, respectively. The fracture characteristics of hydrogen charged specimens were the same as that of SCC specimens. The main stress corrosion mechanism of 7N01-T7 was hydrogen-induced cracking.