Research On Heat Treatment Of7055Aluminum Alloy

In this paper, The effect of temperature, time and cooling methods in the solutiontreatment, aging and cryogenic treatment on the microstructure and mechanical propertiesof the spray forming processed7055aluminum alloy have been investigated, with theanalysis method of tensile test, hardness and conductivity test, OM observation, SEM, TEMand XRD. The conclusions are summarized as following:1) Compared with single stage solution treatment, many of primary phase of Al-Zn-Mg-Cu are dissolved fully and the final microstructure is much easier to be controlled.Therefore, the suitable process of solution treatment is:450℃×3h＋475℃×3h, then cooledin the water at room temperature。2) The best single grade aging treatment on the7055aluminum alloy is120℃holdingtime24h. Under the above process conditions, the peak value of its strength appear, astensile strength is734.3MPa, yield strength is717.4MPa.3) For double stage aging treatment with orthogonal experiment analysis, the agingtemperature of the second step ageing has the most significant effect on7055aluminumalloy property. After ageing treatment in150℃, the phases in intracrystalline precipitationare more tiny and dispersed. The precipitated phases in grain boundary are gathered,coarsening and emerging discontinuous fabrics. So its mechanical properties are improved,including fracture toughness and stress corrosion resistance.4) For tertiary aging treatment with orthogonal experiment analysis, the agingtemperature of the second step ageing has the most significant influence on7055aluminumalloy properties. After ageing process in170℃×0.5h, cooled in the air at room temperature,the intracrystalline precipitated phases are the smaller and more dispersion, the precipitatedphase in grain boundary are bulky, discontinuous and with wider the free zone.5)7055aluminum alloy after cryogenic treatment processing, properties of the alloybecome the stable, while increasing cycle times of cryogenic treatment, the effect is notmore obvious. Based on the comparison and analysis, the best heat treatment process for7055aluminum alloy in this experiment is the solid solution(450℃×3h＋475℃×3h, cooled in theair at room temperature)+tertiary aging treatment(120℃/24h+170℃×0.5h, cooled inthe air at room temperature+120℃/24h). And its tensile strength is688.7MPa,conductivity is38.1%IACS. After the heat treatment process, the mechanical properties of7055alloy are improved. Its strength is increased, and its stress corrosion resistance is alsokept.