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Reduction of coke mixed magnetite ore pellets containing alumina and/or lime has been carried out in a fixed bed with coke powder in the temperature range of 1,100-1,250℃. Degree of metallization of the reduced pellets was obtained from the chemical analysis, and volume change of the reduced pellets was evaluated by measuring pellet diameter before and after reduction. Phase change during the reduction was also investigated by microscopic observation. The results obtained are summurized as follows. (1) As the Al₂O ₃content increases, degree of metallization of the ore pellets decreases and shrinkage of the reduced pellets also decreases. (2) Addition of 5% CaO to the 5% Al₂O ₃ pellets improves the degree of metallization and increases shrinkage of the reduced pellets, especially within the temperature range of 1,200-1,250℃. In the case of 10% CaO addition to the same pellets, however, both degree of metallization and shrinkage decrease. (3) CaO addition to the 10% Al₂O ₃ pellets showed the similar effect to that of 5% Al₂O ₃ pellets on the degree of metallization and shrinkage, showing no conspicuous effect of lime addition. (4) While Al₂O ₃ in the pellets is inhibitive to the reducibility as well as agglomeration, CaO is promotive to the above properties.
For the purpose of ameliorating of toughness by boundary control, Be was added to Al-Li multiphase alloys. Interface behaviors during ageing were investigated by means of the measurements of hardness and tensile strength, and also the observation of optical and transmission electron micrographs. In order to evaluate the fracture toughness, instrumented Charpy impact test was carried out and fracture surface was observed with a scanning electron micrograph. Grain size was refined by α-Be particles that acted on dragging force at grain boundary in Al-Li-Cu-Be alloy. And PFZ half width in Al-Li-Cu-Be alloy was decreased by early precipitation of T₁ phases compared with Be-free alloy. Double eak phenomenon which was observed at the hardness and tensile tests in Al-Li-Cu-Zr-Be alloy may be estmated by the precipitation of secondary T₁ phases due to the change of δ′, T₁ and θ′ phases stability. And considering toughness and elongation, it is possible to think that the secon peak condition may be the most optimum condition of heat treatment because of the remarkable improvement of elongation in Al-Li-Cu-Zr-Be alloy. In case of Al-Li-Cu-Zr alloy containing minor Be, higher impact absorbed energy than that of Be-free alloy was observed. This remarkable improvement of fracture toughness was attributed to the change of fracture mechanism from brittle to ductile mode. the high energy fracture mode of minor Be added alloy was associated with homogeneous deformation due to various interface controls.
The purpose of this study is to investigate the effect of Be addition on the microstructure and mechanical properties of as-cast and homogenization treated Al-Li-(Be)alloys. The ductility of as-cast Al-Li alloy was increased by the addition of Be and the fracture morphology was changed from brittle to ductile mode. Also, hardness and strength have been decreased by homogenization treatment. The morphology of eutectic structure which consists of α(Al) and α(Be) was changed from lammellae to spherical type by homogenization treatment. The shape of α(Be) phase has been revealed as hollow type by TEM observation. It consists of outer surfaces with well defined crystal facets and the core filled with α(Al). The microstructure of as-cast Al-Li-Be alloys showed coarse δ´, fine δ´, and coarse δ phases. The coarse and fine δ' phases were formed at Be-rich phase /matrix interfaces and in matrix, respectively. By homogenization treatment, the δ phase in Al-Li and Al-Li-Be alloys dissolved and the size of δ phase in Al-Li-Be alloys was finer than that of Al-Li alloy.
The microstructure, tensile and impact properties of forgings of 7175 aluminium alloy have been studied as a function of intermediate thermo-mechanical treatment(ITMT) process. The ITMT process is consisted of warm working and recrystallization. In the case that the billet was warm-worked above 60% below 250℃ and recrystallized at 475℃, the grain size revealed about 17㎛ which corresponds to one third of that of conventional process. The refinement of grain size leaded to the improved ductility and impact energy without sacrifice of tensile strength. It was found that the ITMT processed specimen behaved isotropically due to the near equiaxed grains. It was observed that the ITMT processed specimen showed the mixed fracture mode of transgranular and intergranular, instead of intergranular mode. This change of fracture mode contributed to the improved ductility and impact property.