Influences Of Aging Treatment And Zn Addition On Intergranular Corrosion Susceptibility Of Two Kind Of Al-Cu-Li Alloys

Abstract:the intergranular corrosion (IGC) dependence on aging te mper (T6aging at150and175℃, T8aging at150℃) of Al+3.7C u+1.1Li+X and Al+2.6Cu+1.6Li+Y series alloys (X represents0.3M n+0.5Mg+0.11Zr+0.07Ti and Y represents0.3Mn+0.3Mn+0.086Zr+0.11Ti) was investigated. The influences of Zn addition on mechanica1property and corrosion behavior of Al-Cu-Li alloys was also studi ed by potentiodynamic scanning experiment, tensile test and intergra nular corrosion test, using optical microscopy (OM), transmission el ectron microscopy (TEM) and micro-hardness tester. The main concl usions were as follows:1) The corrosion diagram associated with aging process was established. The results showed that according to the corrosion mode variation, the aging process curve was divided into four stages. Stage Ⅰ corresponded to the initial aging stage during which pitting etch or local intergranular corrosion (L IGC) occurred. Stage Ⅱ corresponded to under-aging stage during which general intergranular corrosion (G IGC) occurred. Stage Ⅲ corresponded to near-peak aging stage, during which the corrosion mode was changed to L IGC. Stage IV corresponded to over-aged stage, during which the corrosion mode was changed to pitting and IGC disappeared. The maximum IGC depth was increased first and then decreased with aging time extension.2) In the under-aged alloy, the grain boundary precipitates with small size were distributed continuously, destroying continuous corrosion path. As the aging time extension, both the corrosion potential of alloy and the driving force for grain precipitates dissolution decreased. Consequently, the alloy in under-aged condition were most susceptible to IGC. IGC resistance of alloy in peak-aged condition and over-aged condition were also improved.3) The alloy having relatively high Cu content had rapid aging process and had a narrow range of aging time in which IGC happened.4) Zn addition promoted nucleation of T1phases, improving Al-Cu-Li alloys strength and accelerating its aging process.5) Zn addition could significantly improve IGC resistance of B group alloys, while the similar phenomenon was not observed in A group alloys. The reasons may be that two type alloys had different Cu, Li content.