| 7N01 aluminum alloy is one of the critical structural materials used in the fields such as modern aerospace and vehicle engineering, but the application ranges of this alloy are largely limited by the high susceptibility of localized corrosion. Aging treatment is the critical process during the manufacturing process of the alloy. Corrosion resistance as well as excellent mechanical properties may be achieved simultaneously by an appropriate aging treatment for the alloy. In this thesis, the aging processes of the alloy including peak-aging (T6), two-stage aging, retrogression and re-aging (RRA) and non-isothermal aging have been investigated. Furthermore, the influences of aging process on the microstructure, inter-granular corrosion (IGC), exfoliation corrosion (EXCO), stress corrosion (SC) and electrochemical corrosion, have been analyzed. The relations between the microstructure and the corrosion properties of the alloy have been obtained. The main conclusions are as follows:(1) For 7N01 aluminum alloy, a T6 aging process with 120℃/24h led to a higher strength, and a two-stage aging process with 110℃/4+160℃/8h led to better corrosion resistance properties, while a RRA treatment process with 120℃/24h preaging,180℃/25min retrogression, and 120℃/24h re-aging, or a non-isothermal aging process with (40℃,180℃)@20℃/h+(180℃,120℃)@ 20℃/h led to better comprehensive properties.(2) The inter-granular corrosion of the alloy extended to the inside with the form of a mesh. The exfoliation corrosion of 7N01 aluminum alloy experienced the process described as pitting→ bubbling→auriventris→ layered and lifted erosion→ stratifying and flaking seriously, and the corrosion product was lamellar in shape. The stress corrosion fracture of the alloy belonged to the dimple ductile fracture and there were a large number of dimples and a little corrosion tunnels on the fracture surface, besides there were obviously inter-granular corrosion cracks and secondary cracks on the fracture surface for the alloys in natural aging or T6 aging state. The surface of samples with different aging states all occurred pitting corrosion after an electrochemical corrosion test.(3) The resistances to inter-granular corrosion, exfoliation corrosion and stress corrosion of the alloy were closely associated with the aging process. For different aging states, the corrosion susceptibility of the alloy ranks from low to high as follows:two-stage aging, non-isothermal aging, RRA, T6 aging, natural aging.(4) The corrosion resistance of the alloy is associated with the structure and characteristics of grain boundary precipitates (GBP) and precipitate free zones (PFZ). Under two-stage aging, RRA and non-isothermal aging states, the corrosion susceptibility of the alloy was low, because GBP were coarsened and distributed discontinuously, and the PFZ were rather wide (exceeding 68nm). However, the corrosion susceptibility of the alloy was high under natural aging and T6 aging states due to continuously distributing GBP and inconspicuous PFZ. |
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