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미량 Cr 및 Ti 를 함유하는 Al-Mg-Si 합금의 용질편석과 석출조직
최정철,수총유강,신미창언,고교항부,류성곤 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.5
In Al-1.1wt%Mg-0.68wt%Si alloy the effect of Cr and Ti additions on precipitation behavior of the homogenized and/or aged specimens has been investigated homogenizing. Ephase(Al, Mg, Cr₂) is preferentially precipitated around Mg₂Si and distributed unevenly near a cored dendrite structure. With the addition of Cr and Ti the aged microstructure has indicated that the coarsening of needle-shaped G. P. zone and rod-shaped intermediate phase(β') is delayed, and transition from needle-shaped G. P. zone to β' phase is, thus, delayed. This in turn, caused deceleration of the hardness decrease rate during overaging.
Al-Mg-Si 합금의 응고편석과 (凝固偏析) 균질화거동에 (均質化擧動) 미치는 Cr 및 Ti 의 영향
최정철,수총유강 (手塚裕康),신미창언 (神尾彰彦),고고항부 (高稿恒夫),윤의박 ( J . C . Choe,H . Tezuka,A . Kamio,T . Takahashi,E . P . Yoon ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.1
Microsegregation and its homegenization behavior of magnesium and silicon in Al-1, 1wt %Mg-0.68wt%Si alloy as well as those of chromium and titanium in the alloy have been investigated. Minimum magnesium and silicon concentrations in alpha-dendrite arm are 0.4wt% and 0.2wt% that are one half and one third of each composition, respectively. The concentrations are, however, rapidly homogenizecl at 530℃. Titanium and chromium elements make grain size be greatly refined in Al-Mg-Si alloys but they are remarkably concentrated at the center of alpha-dendrite arm and from a cored structure. The maximum concentrations increase two to three times for titanium and one and a half times for chromium. The concentration of titanium does not appear outside the cored structure but that of chromium is approximately one half of the total ahromium amount. These do not disappear at 530℃ for 100 hours. During homogenization treatment, chromium is deposited as E phase of Al_(18)Mg₃Cr₂ around crystallized compounds and its distribution becomes inhomogeneous.
최정철,장세훈,차용훈,오익현,Choi, Jung-Chul,Chang, Se-Hun,Cha, Young-Hoon,Oh, Ik-Hyun 한국재료학회 2009 한국재료학회지 Vol.19 No.2
In this study, Ti powder was fabricated from Ti scrap by a hydrogenation-dehydrogenation (HDH) method. The Ti powders were compacted by Spark plasma sintering (SPS) and the microstructure and mechanical properties of the powders were investigated. A hydrogenation reaction of Ti scrap occurred at temperatures near $450^{\circ}C$ with a sudden increase in the reaction temperature and a decrease in the pressure of the hydrogen gas as measured in a furnace during the hydrogenation process. In addition, a dehydrogenation process was carried out at $750^{\circ}C$ for 2hrs in a vacuum of $10^{-4}torr$. The Ti powder sizes obtained by hydrogenation-dehydrogenation and mechanical milling processes were in the range of $1{\sim}90{\mu}m$ and $1{\sim}100{\mu}m$, respectively. To fabricate Ti compacts, Ti powders were sintered under an applied uniaxial punch pressure of 40 MPa at in a range of $900{\sim}1200^{\circ}C$ for 5 min. The relative density of a SPSed compact was 99.6% at $1100^{\circ}C$, and the tensile strength decreased with an increase in the sintering temperature. However, the hardness increased as the sintering temperature increased.
Al-Mg 및 Al-Zn-Mg 합금의 미시편석과 균질화 거동에 미치는 Ti 의 영향
최정철 亞洲大學校 1989 論文集 Vol.12 No.-
Microsegregation and its homogenization behavior was investigated the amount of non-equilibrium crystallized and solute concentration of perimary dendrite arm in Al-9.4%Mg and Al-4.75%Zn-1.5%Mg alloy with /without Ti. The amount of nonequilibrium crystallized phase increases and miniumm solute concentration of primary dendrite arm decreases with Ti addition; microsegregation degree increases as well. The homogenization of Ti-added alloy is slower than that of non-added alloy attthe early stage. The homogenization of Ti-added alloy is not completed although the alloy is heat-treated for over 100 hours and the microsegregation remains at the low concentration region of magnesium and zinc in Ti-rich structure, which is same as cast. According to the diffusion couple for Al-2%Mg/Al-2%Mg-0.15%Ti alloys, those results indicate that because Ti is hardly diffused at common homogenization temperature, only maegnesium and zine is diffused and the chemical potential is to be equilibrium at the condition of lower zine and magnesium concentration than of a matrix, outside of Ti-rich structure.
용탕단조 마그네슘합금의 조직과 기계적 성질에 미치는 Zn 과 Zr 의 영향
최정철,최영두,장시영 한국주조공학회 1999 한국주조공학회지 Vol.19 No.5
Mg-Zn-Zr ternary alloys containing 6wt% Zn and (0, 0.4, 0.6)wt% Zr, which is added for grain refinement, can be cast into complex shape by squeeze casting. The influence of Zn and Zr as additional elements on microstructure and mechanical characteristics is investigated by OM, SEM, WDX, XRD and microvickers hardness measurement. The microstructure of Mg-Zn-Zr alloys consists of primary α-Mg and MgZn eutectic compound between dendrites. The grain size is decreased from 136㎛ to 97 ㎛ by Zr addition, resulting in that the hardness is increased from 42Hv to 59Hv. Furthermore, the grain size is changed to 83β○ and the hardness is increased to 65Hv by additional infiltration pressure. These results indicate that the Zr addition and additional infiltration pressure are effective for grain refinement acting as an important factor to increase the hardness. The increment in hardness by the Zr addition is slightly larger than that by the additional infiltration pressure. (Received August 20, 1999)
Ti에 의해 결정립 미세화한 Al-Cu 및 Al-Cu-Mg 합금주괴에 있어서의 미시편석
최정철 亞洲大學校 1989 論文集 Vol.12 No.-
Microsegregation of solute elements with titanium and its homogenization behavior of titanium itself are studied in Al-4.5%Cu alloys. The microsegregation and their solutionization process at 530℃ are determined by concentration analyses and structural observations. It is found that microsegregation degree increase, that minimum solute concentration decreases and that the amounts of crystallized compound increase as titanium elements increase. The findings were analysed by another examination: the diffusion of copper is examined in Al-4.5%Cu alloys with/without titanium. As the titanium element segregated markedly. Ti-rich cored structure was formed. The structure did not vanish at the solutioninzation temperature and time of copper and magnesium elements. Therefore the results can be suggested that segregated titanium affects the following treatments such as aging.