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Al-Li-(Cu , Zr) 합금에서 시효에 따른 δ' 상의 형상 및 입자크기분포의 변화
우기도,조현기 ( K . D . Woo,H . K . Cho ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.2
The present work was aimed to examine the changes of the shape and particle size distribution(PSD) of δ` particles on ageing in Al-Li-(Cu, Zr) alloys which had low density, high specific strength and stiffness. Increasing ageing time and temperature resulted in particles whose aspect ratio tended toward 1. The aspect ratio of δ` particles was not dependent upon the ageing temperature and time in Al-Li-Cu alloy but was dependent upon them in Al-Li-Zr alloy. The PSD of δ` particles in Al-Li-Zr alloy skewed to the right hand compared with that in Al-Li-Cu alloy, because Al₃Zr phase in Al-Li-Zr alloy formed before ageing promoted the precipitation and growth of δ` phase. Therefore, the PSD of the δ` particles was found to be affected by the presence of Al₃Zr particles. The growth rate of δ` phase was not affected by the existence of the third transition phase T₁formed by the addition of Cu in Al-Li alloy but was affected by the existence of Al₃Zr formed by the addition of Zr in Al-Li alloy.
Al-Li-Cu-Mg-Zr 합금에 있어서 δ' 상 조대화를 위한 Lithium의 확산계수 평가
정동석,김은석,조현기( D . S . Chung,E . S . Kim,H . K . Cho ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.1
The evaluation and analysis of diffusivity of lithium for coarsening and coarsening kinetics of δ` precipitate in Al-Li-Cu-Mg-Zr alloy aged at 170℃ have been investigated by transmission electron microscopy. With ageing time, δ` precipitate coaesened to followed γ ̄∝t^(1/3) and coarsening kinetics was found to be obeyed to the Lifshitz-Slyozov-Wagner(LSW) theory and diffusivity of lithium for coarsening of δ` precipitate in Al-Li-Cu-Mg-Zr alloy was obtained to be 5.85×10^(-17)∼1.53×10^(-16) by experimental coarsening rate constant and various coarsening kinetic theory. Diffusivity of lithium measured by using various model but MLSW and Tsumuraya(VI) et al. model in Al-Li-Cu-Mg-Zr alloy is similar to that calculated by the Costas`s diffusivity equation. It was, therefore, suggested that additing to the Cu, Mg and Zr element in Al-Li system have no great effect on diffusivity of lithium for coarsening of δ` This suggest that in matrix.
Al-Cu-Li-Mg-Ag-Zr합금의 시효에 따른 전기화학적 분극 거동과 공식특성
민병철,정동석,손태원,조현기 ( B . C . Min,D . S . Chung,T . W . Shon,H . K . Cho ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.2
In this paper, we studied on both electrochemical polarization behaviors and pitting characteristics of ultra high strength Al-Cu-Li-Mg-Ag-Zr alloys(named C1 and C2) and 2090 alloy according to their treatments in the deaerated 3.5% NaCl, using by the potentiodynamic and the potentiostatic method; SEM micrograph and surface roughness including depth of pitting attack. With the cyclic polarization curves, the hysteresis of the C1 and C2 alloys appeared more remarkably than that of the 2090 alloy, because of precipitation microstructural difference between C1, C2 alloys and 2090 alloy. In the pitting experiments, the correlations between pitting growth and aging conditions were analyzed with the SEM micrograph and measurement of the pit depth.
Al-Li-Cu-Zr합금의 시효에 따른 인장파괴모드변화에 미치는 미세조직의 영향
정동석 ( D . S . Chung ),이수진 ( S . J . Lee ),조현기 ( H . K . Cho ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.3
To clarify the influence of precipitation microstructure and inclusion on the monotonic tensile fracture behaviors in 2090 alloy aged at 180℃, the detailed measurement of hardness, tensile strength, elongation and the observation of scanning electron micrography, transmision electron micrography have been carried out. The transgranular shear ductile fracture has been observed in specimen quenched after solution treatment at 500℃ for 45min. While the undet-aged specimen was fractured in both transgranular shear ductile and intergranular fracture.mode, the fracture mode of peak-aged and over-aged alloy was predominantly intergranular fracture. The fracture behavior of each ageing condition was influenced by the change of precipitation microstructural features. In the case of peak-aged and over-aged alloys, the coarse and heterogeneous slip band caused by both shearable nature of the δ`(Al₃Li) precipitates and PFZ along the high angle grain boundary aid the localization of deformation, resulting in low energy intergranular fracture. It was also estimated that the fractured T-type intermetallic phases (inclusion) and the equilibrium δ(AlLi) phases which were formed at grain boundaries palyed an important role in promoting intergranular fracture mode.