| In order to advocate energy conservation, low-carbon environment and agree with lightweight of automobile, the "Going Global" strategy of large aircraft and high-speed rail. The studying of high-strength aluminum lightweight materials has become a hot spot and made remarkable achievements. However, it remains our goal to pursue aluminum alloy material which has high-strength and high-toughness, resistance to fatigue, corrosion resistance and low cost. In this paper, the effects of main elements, trace elements, rolling process, homogenization process and solution treatment process on the micro-structure, mechanical property, fracture mechanism, electric property and exfoliation corrosion resistance were investigated by using room temperature tensile test, Vickers-hardness, exfoliation corrosion and electric conductivity measurement, optical microscopy (OM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy spectrum analysis (EDS) and electronic microscopy (SEM, TEM) analysis. Several conclusions can be summarized as follows:(1) The grains are refined and the amount of precipitation phase is promoted with the increase of Zn and Mg content in the range of experiment. While much higher content results in coarsening grains and gathering precipitation phase. When the Zn and Mg content is 8.1% and 2.8%, the optimal tensile strength, yield strength, elongation and hardness in the T6 condition is 715MPa,658MPa,13.3% and 227HV, respectively. The conductivity and the ability of exfoliation corrosion resistance of Al-Zn-Mg-Cu-0.25Ce alloy decrease gradually with the increase of Zn and Mg content. It shows that the addition of Zn and Mg can reduce resistance to stress corrosion of the alloy.(2) As-cast grain is refined obviously by adding Ce or Zr or combined addition, it can obtain equiaxed fine-grained structure and optimum mechanical properties by combined addition of Ce and Zr. The optimal tensile strength, yield strength, elongation and hardness in the T6 condition is 722MPa,662MPa,13.3% and 228HV, respectively.(3) The ingot of Al-8.1Zn-2.8Mg-2.0Cu-0.25Ce alloy by conventional melting and casting presents dendritic micro-structure, with non-equilibrium eutectic phase distributed along the grain boundary, and the dissolution temperature of low melting point eutectic is 467.3℃. After homogenized at 455℃×16h+465℃×4h+475℃×4h, the alloy elements are uniformly distributed with little pseudo-eutectic, and tensile strength, elongation and conductivity is relatively optimal.(4) The triple-strengthening-solution treatment (450℃×90min+465℃×40min+ 475℃×20min) promotes the dissolution of coarse second phase and eutectic phase, after being treated by peak aging, the strengthening effect of alloy will be better due to the precipitation of more fine dispersed particles in the matrix. The optimal tensile strength, elongation in the T6 peak aging and solid solution state is 715MPa/592MPa, 13.3%/22.9%, respectively. The conductivity and rank of exfoliation corrosion in the T6 condition is 34.5%IACS and EA+.(5) After optimized triple-homogenization, triple-strengthening-solution treatment and rolling process of four passes hot rolling with 80% total processing ratio, five passes cold rolling with 50% total processing ratio, the micro-structure and mechanical properties of Al-8.1Zn-2.8Mg-2.0Cu-0.25Ce-0.25Zr alloy sheets in the rolling annealed and T6 condition are the best. The tensile strength, elongation and hardness in the rolling annealed and T6 condition is 315MPa/748MPa,10.2%/14.2%,102HV/245HV, respectively. Compared with other domestic developed 7XXX alloys, this alloy exhibits ultra-high strength and good ductility. The conductivity properties of four different rolling process programs is #2>#4=#1>#3, meanwhile, the rank of exfoliation corrosion is EB+, EA, EC and EB, respectively. In summary, under the premise of no rolling crack, the comprehensive performance can be improved by using fewer hot rolling passes with large pressing down quantity and more cold rolling passes with small reduction in the rolling process of high strength aluminum alloy. |
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