Tensile And Intergranular Corrosion Properties Of Al-Zn-Mg-Cu Alloy After Heat Treatment

Super strength aluminum alloy consists mainly of Al-Zn-Mg-Cu serial alloys, its tensile strength is higher than 500 MPa, and have been applied in different business(aviation especially) due to higher specific strength, higher specific stiffness and excellent process ability, as one of the most important materials for this industry. Al-Zn-Mg-Cu serial alloys have also been used widely as structural materials on aeroplanes because of their high strength and low density. During practical service of these alloys, corrosion phenomena are inevitable.Thus, studying both corrosion resistance and mechanical properties after corrosion are very fundamental to the evaluation of material reliability and life.In this paper, microhardness test, tensile test, optical microscope and the scanning electron microscope are used, and the effects of T6(120 ℃ ×24h) aging and T76(120 ℃×5h+153 ℃ ×16h) aging after strengthening solution(470 ℃ ×2h+480 ℃ ×2h+490 ℃ ×2h) on hardness, tensile properties and intercrystalline corrosiveness of the aluminum alloy were investigated. Furthermore, the kinetics of intergranular corrosion and corrosion rate were also studied.It is shown that: after strengthening solution and T76 aging process, the second phase are fine, dispersive and larger in Al-6Zn-2Mg-2Cu aluminum alloy and almost evenly distributed in intragranular and the continuous distribution of grain boundary precipitates are observed.The size of the grains become finer. On the contrary,after strengthening solution and T6 aging process, the second phase are bigger and the distribution is segregated in intragranular.Precipitate in grain boundary distributed intermittently and the size of the grains became lager.The tensile strength for Al-6Zn-2Mg-2Cu alloy of T6 aging is 570 MPa and the elongation is10.10%. For the Al-6Zn-2Mg-2Cu alloy of T76 aging, the tensile strength is 545 MPa and the elongation is 11.97%. Relative to the Al-6Zn-2Mg-2Cu alloy of T6 aging, the ductility increased by 18.7%, while the strength remains essentially unchanged at the same time. The maximum corrosion depth of two aged alloy after 6h corrosion are both accordance with normal distribution rather than extreme value distribution. The weight loss equations are as below: For T6 aging, y=0.2826x0.6106, and y=0.2435x0.6495 for T76 aging. Depth equations, forT6 aging, y=7.72673x0.43702, and y=6.43898x0.43698 for T76 aging. The corrosion rate are both increasing rapidly in 0~1.5h, and then begin to fall and decline slowly. For T6 aging,average corrosion rate is 0.0513mm/a, and the uncertainty is 0.45%. For T76 aging,average corrosion rate is 0.0339mm/a, and the uncertainty is 0.44%.