| The7050aluminum alloy based on7075is a new kind of high strength, high toughness, and anti-corrosion aluminum alloy due to the development of heat treatment. Its main alloy components of Zn, Cu and Mg are optimized; Zr is added instead of Cr and Mn; the contents of Fe and Si are substantially reduced impurity. At present, the domestic research of the7050alloy sheet is at the stage of imitation and test. While there is a big gap between china and western countries related to technology for heating processing, mechanical properties and anti-corrosion properties. In this work, aging treatment, microstructure evolution and corrosion behavior of the7050alloy are studied, which aims at providing some theoretical and experimental foundation for the improvement of mechanical properties and corrosion resistance of the7050alloy.The strength, hardness, conductivity and microstructure evolution of the7050alloy after single-stage, two-stage and RRA heat treatment were studied by tensile test, hardness testing, conductivity testing, metallography and transmission electron microscopy analysis. The results showed that the main strengthening phase of the7050alloy in different aging process is η’phase. The alloy strength, hardness and conductivity related to the nature and distribution characteristics of the precipitated phases. The alloy obtained the highest peak hardness of196.3and the conductivity of20.0MS/m after120℃aging24h. Meanwhile, the tensile strength, yield strength and elongation were601MPa,538MPa, and13.9%, respectively. It was proved that the7050alloy had higher strength but poor corrosion resistance after a single-stage aging. The suitable two-stage aging treatment for the7050alloy was:120℃/6h+165℃/16h. Under this condition the hardness was180.7and the conductivity was23.3MS/m. meanwhile, the tensile strength, yield strength and elongation were558MPa,504MPa and12.5%, respectively. At two-stage aging the strength and hardness of the alloy decreased while its corrosion resistance was improved. The suitable regression re-aging process for the7050 Alloy is:pre-aging of120℃C/24h;170℃/120min regressions and120℃/24h reaging. In this condition, the tensile strength, yield strength, elongation and conductivity were596MPa,575MPa,12.4%and23.5MS/m, respectively. The7050alloy obtained high strength and good corrosion resistance under the RRA treatment.The intergranular and exfoliation corrosion behaviors of the7050alloy under different aging treatment are studied using metallurgical and accelerated corrosion test. The results showed that the order of the corrosion resistance of the7050alloy at single-stage aging was: overaging> peak aging> under aging. The maximum corrosion depths of intergranular corrosion at120℃aging2h,24h and48h were58.861,45.851and29.512μm, respectively. The corrosion resistance of the7050alloy after two-stage aging increased with the increase of aging time. The maximum corrosion depths of intergranular corrosion after165℃final aging Oh,3h,12h and24h were50.312,46.658,31.236and20.586μm, respectively. While the levels of exfoliation corrosion after48h were EC, EB, EA and EA. The corrosion resistance of the RRA regression increased with the increase of time. The maximum corrosion depths of intergranular corrosion after170℃regression aging15min,120min and200min were67.051,56.036and26.236μm. While the levels of exfoliation corrosion after48h were ED, EB and EA. |
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