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Al-Li-Cu-Mg-Zr 계 합금분말 압출재의 기계적 성질에 미치는 석출물의 영향
나형용,이동수,이성의 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.12
The changes of microstructures and mechanical properties of Al-Li-Cu-Mg-Zr P/M alloy with various composition and extrusion variables were observed. Increasing Li content, yield stress increases but tensile stress decreases because of increasing intermetallic phases and δ phase formation. As the extrusion temperature get higher from 573K to 773K, the larger size of subgrain is obtained. Besides in case of extrustion at 773K, composite precipitates are precipitated in the matrix. The mechanical properties of extruded bars-Y.S. (570MPa), E.L. (2.6%)-were obtained by the finer microstructure. The reason is considered that composite precipitates derived cross slip or Orowan by pass of dislocation and Zr acted as grain refiner to suppress recrystallization.
급속응고한 Al-Fe-Mo-Si 계 합금분말 압출재의 고온 성질에 관한 연구
나형용,최주태 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.3
The microstructure and properties of the rapidly solidified Al-8Fe-2Mo-1.5Si alloy for elevated temperature applications were investigated. The effects of Mo on thermal stability and Si on fracture toughness through the observation of microstructure, hardness test and tensile test were described. The mechanical properties of extrudates with the variation of extrusion ratio and size distribution of powder were investigated. Hardness of smaller powder(50㎛) was superior to that of larger powder(150㎛). The extrudate consolidated with finer powder size distribution (10∼100㎛) yields higher strength than that with a coarse size distribution(100∼200㎛). The tensile strength of 2nd extruded bar which was consolidated with finer powders was 520MPa at 25℃, 310MPa at 275℃. The deterioration of mechanical properties at elevated temperature was due to the decomposition of Zone A and metastable phase Al_6Fe into stable phase Al₃Fe and the growth of needle-like Al₃Fe precipitates. Quarternary Mo and Si containing alloys showed uniform dispersion of fine cuboidal-polygonal precipitates, bcc Al_(12)(Fe,Mo)₃Si phase which displayed a remarkable resistance to coarsening.
Al-Li-Cu-Mg-Zr 계 합금분말의 응고조직과 압출재에서의 석출물에 대한 고찰
나형용,이동수,이성의 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.9
AL-Li-Cu-Mg-Zr alloy powders were manufactured by gas atomizer and then extruded. The microstructures and mechanical properties of alloy powders and extruded bars were studied. The microstructures were typical cellular structure and icosahedral phases were crystallized out on the cell boundaries in Al-3Li-3Cu-1Mg-0.3Zr, Al-3Li-3Cu-1Mg-0.1Zr and Al-4Li-3Cu-1Mg-0.1Zr alloy powders. But increasing Li/Cu ratio, icosahedral phase and T_B, phase were crystallized out simultaneously. In Al-3Li-3Cu-Mg-Zr alloy extruded bars, almost the precipitates were icosahedral phase and Type 1 phase appeared. In Al-3Li-1.5Cu-Mg-Zr alloy extruded bars, the precipitates were almost R phase. In Al-3Li-1Cu-Mg-Zr alloy extruded bars, the precipitates were almost C phase. Therefore, In AI-Li-Cu-Mg-Zr alloy extruded bars, precipitation mode is Icosahedral phase → Type 1 → Type 2 → R → C phase appeared according to increasing Li/Cu ratio.
급속응고한 Fe-3.7wt% C-Cr 계 합금분말 압출재의 미세조직과 기계적 성질
나형용,김동익 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.12
The purpose of this work was to develop an engineering materials having a high volume fraction of carbide. For this purpose, rapidly solidified Fe-3.7wt%C-(1∼4)wt%Cr alloy powder was made using high pressure gas atomizer and followed by hot extrusion. In this study, the microstructures and mechanical properties of extruded bars were discussed. The microstructures of extruded bars were found to be the mixture of carbide and fine pearlite. The average carbide particle size was about 2㎛ and the pearlite lamellar spacing was about 0.1㎛. The tensile strength increased with increasing extrusion ratio and reached 85∼90㎏/㎟ when extrusion rate was 13. Toughness was 4∼5㎏/㎟ when extrusion race was 13. Toughness was 4∼5㎏ m/㎠ and hardness was 55∼60 HRc.