| 7xxx series aluminum alloys have been widely used in the aviation industry and transportation fields, due to their desirable high specific strength, fracture toughness and corrosion resistance. The aim of the investigation is to ga in experimental evidence for the influence of heating rate, solution temperature and holding time on microstructure and properties of a novel super- high strength Al-10.78Zn-2.78Mg-2.59Cu-0.221Zr-0.047 Sr aluminum alloy, which studied by electron back-scattered diffraction, X-ray diffractometer, optical microscopy, scanning electron microscope, energy dispersive spectrometry, Vickers hardness and tensile test, electrical conductivity test, intergranular and exfoliation corrosion experiment. The main work and conclusions are as follows:(1) Internal relations between properties, microstructural and main factors(heating rate, solution temperature) of the initiation of as-extruded aluminum alloy was studied. The results show that solution temperature and heating rate has little effect on the microstructure. With increasing solution temperature, the Vickers hardness decreased first and then increased, conductivity increased first and then decreased, there was a negative correlation between micro-hardness and conductivity. Increasing the heating rate would be increase hardness and decrease conductivity of the as-extruded alloy. Up to 470℃, heating rate has little effect on the hardness and conductivity.(2) Effect of subsequent hot compression process(pre-heating: 400℃/2h, deformation: 40%) on microstructure and properties was studied. The results show that both plastic deformation and dynamic rectystallization occurred during the hot compression, leading to the deformation energy storage enhanced, lattice distortio n was severe and dislocation density increased. As solution temperature increased, the percentage of small angle grain boundary increased, the ability of inhibit recrystallization enhanced. Increasing heating rate, the grain grew up, improve the degree of recrystallization and grain equiaxed. Up to 470℃, rapid heating rate can suppress recrystallization. Hot compression decreased the hardness and increased the conductivity of as-extruded al oy.(3) After rapid or slow heating rate(3.6℃/h, 180℃/h) continuous heating up to 470℃, followed by solution treatment at 470℃ for 2, 24 hours, quenched with water and then aged for 24 hours at 121℃, the microstructure and properties was investigated. The results showed that tensile strength, yield strength, elongation are 735.6MPa, 691.7MPa, 6.1% respectively and the alloy achieved best performance when heating rate is 180℃/h, solution temperature is 470℃ and holding time is 2h.The fracture mode is dimple fracture. Along radial section of the ingot, the grain showed fine equiaxed, micro- hardness and conductivity were 218.1HV and 25.9%IACS, the depth of intergranular corrosion was 66.23μm and exfoliation corrosion ranked PB; Along axial section, the grains are elongated, micro- hardness and electrical conductivity were 223.9HV and 26.0%IACS, the depth of intergranular corrosion was 77.91μm and exfoliation corrosion ranked EC+.(4) Microstructure and properties of the hot compression aluminum alloy under rapid/slow heating- water quench-T6 aging treatment was investigated. The results showed that tensile strength, yield strength, elongation are 708.7MPa, 661.9MPa, 8.1% respectively and the alloy achieved best performance when heating rate is 3.6℃/h, solution temperature is 470℃ and holding time is 2h.The fracture mode is dimple fracture. Along radial section, the grain showed fine equiaxed, micro- hardness and electrical conductivity were 218.9HV and 25.3 %IACS, the depth of intergranular corrosion was 63.01μm and exfoliation corrosion ranked PC; Along axial section, the grain transformed fibrous elongated grains into equiaxed, micro-hardness and conductivity were 211.4HV and 25.7%IACS, the depth of intergranular corrosion was 61.31μm and exfoliation corrosion ranked EB.Research shows that the aluminum alloy exhibits good strength and elongation after hot compression deformation, the depth of intergranular corrosion decreased and the initial deformation stored energy increased. Increasing the heating rate would be decrease the small angle grain boundary, improve the degree of recrystallization. With the holding time extending, the grain size grew up, intergranular corrosion resistance decreased, and little change in hardness, conductivity and exfoliation corrosion performance. |
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