The passive film-induced stress and the susceptibility to SCC of 7050 aluminum alloy in 3.5%sodium chloride solution at various pH values were investigated by slow strain rate testing（SSRT） and flowing stress differential method.The results showed that the passive film-induced stress and the susceptibility to SCC decreased with increasing pH values when pH≤7,while they increased with increasing pH values when pH7.However,the corrosion type was interpreted as exfoliation corrosion when pH=l and 14,and there was no film formed on the surface of the specimens.The whole variation plots of film-induced stress and the SCC susceptibility with pH values were both presented as a valley shape.The symbol and amount of the film-induced stress were related to the compositions of the passive film,which were analyzed using X-ray photoelectron spectroscopy（XPS）.
In this paper,the effect of cathodic polarization on corrosion behavior of AA7003 under three kinds of aging treatments(including peak aging(PA),double peak aging(DPA)and regression re-aging(RRA))was studied in 3.5 wt%sodium chloride solution through slow strain rate testing(SSRT)and electrochemical testing.X-ray diffraction(XRD)and scanning electron microscopy(SEM)methods were also applied to investigating corrosion behavior and fracture morphology.The results showed that under open circuit,stress corrosion cracking(SCC)of AA7003 might by classified as anodic dissolution.In this case,the extent of SCC susceptibility(ISCC)of AA7003 alloy with different aging treatments was as follows:ISCC(PA)>ISCC(DPA)>ISCC(RRA).On the other hand,stress corrosion cracking(SCC)of AA7003 under cathodic polarization might be classified as hydrogen embrittlement(HE)which had been proved in this paper by presence of AlH3 diffraction peak in XRD patterns.In this case,for AA7003 with any of the three aging treatments,hydrogen embrittlement susceptibility(IHE)increases with negatively shifting of cathodic polarization.
In order to study the effects of aging treatment on the intergranular corrosion（IGC） and stress corrosion cracking（SCC） of 7003 aluminum alloy（AA7003）, the intergranular corrosion test, electrochemical test and slow strain rate test（SSRT）, combined with optical microscopy（OM） and scanning electron microscopy（SEM） as well as transmission electron microscopy（TEM） observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged（PA） temper is the lowest, with double peak aged（DPA） the moderate, and retrogression and re-aging（RRA） the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones（PFZ） of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility（ISCC） of AA7003 for three tempers follows the order： ISCC（RRA）
