Al-Zn-Mg-Cu high strength aluminum alloy have been widely applied toaerospace industry because of the excellent characteristics, such as high strength, lowdensity, good toughness, corrosion resistance, and so on. In order to provide scientificand practical basis for making an appropriate heat treatment process and improvementof the alloys mechanical properties, the heat treatment process, microstructure andproperties of7XXX alloys were investigated.In this paper, a satisfied heat treatment process which improve greatly themechanical properties of7XXX alloy was determined through DSC and orthogonaltest and the effects of duplex ageing condition on the microstructure, ageingprecipitation and strengthening behavior of alloys were investigated by lightmicroscope, TEM and HREM.The result of DSC shows that475℃is the7XXX alloy overburnt temperature.Dissolution of surplus phases in alloy is fully development when the solutiontemperature is470℃and heat preservation time is1hour. The optimal single solutionheat treatment is470℃/1h.Though orthogonal test, factors which affect hardness from strong to weak in thefollowing order were found: second-step ageing temperature, second-step ageing time,first-step ageing time and first-step ageing temperature. And factors which affectconductivity are from strong to weak in the following order: second-step ageingtemperature, second-step ageing time, first-step ageing temperature and first-stepageing time. The second step aging temperature is the key factor in double agingparameters, which mainly decide the final properties of7XXX alloy. Alone with thesecond-step ageing temperature increased, the alloy hardness is reduce andconductivity increased.Tensile strength, yield strength, specific elongation and electrical conductivity ofthe alloy are750.27MPa,562.57MPa,26.43%and31.9%IACS, respectively afterduplex aging (120℃/4h+147℃/8h) which improves conductivity of alloy obviouslywith preservation of satisfied mechanical properties.The results of TEM and HREM shows that during the peak double-ageingprocess, strong age-strengthening response is due to the precipitation of GP (both GPIand GPII) zones and GPII zone are major precipitates at this stage. For470℃/2h solution treatment+120℃/30h aging treatment the alloy achievethe first dardness peak point,ane there just have a little change in the alloy’s hardnesswith the increase of aging time after it, and in this aging system the alloy’s resistanceto intergranular corrosion and comprehensive performance is well, so we determinethe optimum heat treatment process of7XXX aluminum alloy:470℃/2h solutiontreatment+120℃/30h aging treatment.With the improvement of the electrical conductivity,resistance to intergranularcorrosion of the alloy can improve. |