Study On Microstruture And Properties Of 7150 Alloy During Heat Treatment

Al-Zn-Mg-Cu alloys with high strength are widely used in aero field. However, this series alloys have high strength, but their stressing corrosion properties are very bad, restrict this alloy's application. Retrogression and re-ageing treatment can improve their corrosion performance, make the comprehensive properties of alloys better. Though domestic researchers do a great deal of work in this area, also obtained very big achievement, all mainly stay around a laboratory stage, never see report of industrialization. The research purpose of this topic is attention on the alloy's practical. The microstructure and properties of Al-Zn-Mg-Cu with solution treatment and retrogression and re-ageing treatment were studied.The result research of solution treatment shows that the time of single solution has little effect on mechanical properties of the alloy, but the temperature has more effect. The strength and hardness of alloy increased with the solution's temperature rose, but when the temperature above the temperature of overburning, the properties of the alloy began to drop. According to the analysis test technology of DSC, we can know that the first solution can make the temperature of melting up, this can make the temperature of second solution above the temperature of overburning, increased the supersaturated degree of body, result in increasing the effect of ageing strength of alloys.The result research of retrogression and re-ageing shows that according to the one-stage and two-stage ageing, the mechanical properties of the alloy with retrogression and re-ageing treatment is better. The temperature and the time of retrogression have more effect on mechanical properties of the alloy, the mechanical properties of the alloy is dropped with the temperature of retrogression. And the degree of influence is related to the thickness of the alloys, the best process to the sheet alloy is not the best to the thick plate, in this experiment, the best process of the thick plate alloy is 120℃,24h+220℃,1h+120℃,24h, its strength is lower than the single ageing, but the conductivity be higher, closed to 38%IACS, can satisfy practical request, and the properties of alloys were better than the United States aluminum standard. In the same of ageing condition, the mechanical properties of the thick plate of alloys in the thick direction appeared two rules: one is that the properties is dropped from the surface to the central, the other is that the properties of medium is high, and the surface and the central is lower. The conductivity of the thick plate of alloys is nearly changed, the extent of the exfoliation corrosion is dropped gradually. The precipitates within the grain had a little changed and the precipitates at the grain boundaries had nearly changed. The size and the distance of the particle of the precipitates within the grain were increased with the temperature rose and the time of retrogression extended. The dominant tensile fracture mode of alloy changed from shearing fracture to dimpled fracture and intergranular fracture.