Including The Study Of The Corrosion Behavior Of Al-cu-li-zr Alloy

An ingot of alloy whose composition is Al-3.5Cu-1.5Li-0.10Sc-0.12Zr was prepared by using water chilling copper mould ingot metallurgy processing which protected by active flux and inert gas.The ingot was homogenized,hot rolled,annealed and cold rolled into a sheet with thickness of 2.3 mm.The effects of different aging systems on its intergranular and exfoliation corrosion properties of the alloy were studied.The mircrostructure of the alloy was investigated by using optical microscopy,scanning electronic microscopy and transmission electronic microscopy.The mircrostructure effected by heet treatment was investigated.The development process and the principle of the corrosion were also studied.The conclusions can be summarized as follows:1.The intergranular and exfoliation corrosion tendencies of Al-Cu-Li-Zr alloy containing Sc increased as the aging temperature increased and the aging time increased at 160℃.The corrosion susceptibility of the alloy was as follow: 130℃/50h＞160℃/40h＞190℃/5h;NA＞UA＞PA＞OA.2.The main reasons of corrosion susceptibility were T1 phase and PFZ.There was a little T1 phase distributed in short-term-aged or low-temperature-aged alloy,which was the reason of the well corrosion susceptibility;The corrosion properties went to bad when the aging time prolonged and the aging temperature increased.Thick T1phase,some balance phases and PFZ appeared,which caused the worst corrosion properties.3.Contrast with the T6 state,The T8 state of the alloy had the more corrosion susceptibility for the more dislocation density and the wider PFZ in the alloy after pre-deformated.The most depth of intergranular corrosion is from 137.5um in T6 state to 191.5um in T8 state;and the exfoliation corrosion grade level from EC in T6 state to ED in T8 state.Electrochemical test also showed the similar law.4.The suitable double ageing treatment of the alloy is 120℃/2h+160℃/24h. At this condition,the tensile strength,yield strength,elongation and conductivity of the alloy is 551MPa,517MPa,7.2%and22.9%IACS.Compared with T8 peak-aged state,double ageing can heighten the elongation with 1.1 percent,the conductivity with 25.1 percent and remain high level of strength.5.After double ageing,the GP zones and the T₁ phase distribute more dispersively and homogenously in the alloy,intermittent precipitation and narrower PFZ in the grain boundaries,which do something with the high level of elongation and the better of the corrosion properties.6.In the entire process of electrochemical impedance testing,the total corrosion impedance of alloy drop firstly and then increase,which reflects the transformation of The main reasons of the total impedance om surface oxide film of the alloy to the corrosion product layer of the alloy.7.The corrosion of the alloy begins with the dissolution of T1 followed by the dissolution of PFZ.