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7XXX계 단조재의 피로 및 파괴인성에 미치는 제조공정의 영향
이오연,임재규,송기홍,손영일,은일상,신돈수 ( O . H . Lee,J . K . Lim,K . H . Song,Y . I . Son,I . S . Eun,D . S . Shin ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.3
The purpose of this study is to investigate the effect of impurity level and fabrication processes on the strength, fracture toughness and fatigue resistance of 7075, 7050 and 7175 high strength aluminum forgings. It has been verified that plane strain fracture toughness and fatigue characteristics of a specially processed 7175S-T74 alloy is superior to a conventionally processed 7075-T6/T73, 7050-T74 and 7175-T74 alloys. These beneficial effects primarily arise from two view points, i.e., the effect of reducing the impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as Al_7Cu₂Fe and Mg₂Si. Futher reduction of the amount of nonequilibrium second phase particles has been observed by applying a special fabrication process.
7175 합금 단조재의 미세조직과 기계적 성질에 미치는 중간가공열처리 영향
이용연,송영범,손영일,이경훈,은일상 ( Y . Y . Lee,Y . B . Song,S . T . Im,Y . I . Son,K . H . Lee,I . S . Eun ) 한국열처리공학회 1997 熱處理工學會誌 Vol.10 No.3
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.
Al-Li 2 원합금에 있어서 δ' 상의 초기분해과정과 조대화거동에 미치는 Be 첨가의 영향
조현기,정동석,은일상 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.2
To clarify the influence of Be addition on the coarsening behavior and the early stage of decomposition process of δ´phase in binary Al-Li alloys, the detailed measurement of micro vickers hardness and specific heat and the observation of transmission electron micrographs have been carried out. Al-Li-Be alloys were found to have higher hardening rate than the binary Al-Li alloy when aged at 190℃ and Be addition on binary Al-Li alloys promoted the early stage of decomposition process of metastable phases such as formation of ordered domains (δ´precursory structures). δ´precursory structures in the binary and ternary alloys were stable with aging time at 190℃. The split of endothermic peak R on the S-T their incompletely orderd structure and size effect, respectively. It was deduced that the coarsening rate constants of δ´phase in Al-Li-Be alloys were higher than that of the binary Al-Li alloy because of the change of interfacial characteristics of δ´phase which resulted from microsegregation of Be at interface between δ´phase and the matrix or Be incorporation into δ´phase.
조현기,은일상,유병호,박수동,백정우 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.8
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.