• 동력기계공학회지
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• 제18권6호
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• pp.29-33
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• 2014

The electrochemical characteristics of Al-Si casting alloys (Al-10%Si, Al-9%Si, Al-7%Si) in 3.5% NaCl solution at room temperature was studied using potentiodynamic techniques. The electrochemical values of corrosion potential($E_c$), corrosion current density($I_c$) and corrosion rate(mpy) were examined. The Al-Si alloys had several compounds such as $Mg_2Si$, ${\pi}$-$Al_8Si_6Mg_2Fe$ and $Al_2CuMg$ which could affect corrosion resistance significantly. The potentiodynamic polarization curve exhibited typical active behavior in anodic polarization curve. The major corrosion mechansim for the Al-Si alloys were pitting and grain boundary corrosion. As increasing Si and Cu contents, their corrosion resistance was decreased.

• 청정기술
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• 제28권1호
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• pp.1-8
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• 2022

미활용 저급자원인 석유코크스를 대상으로 고순도의 수소 생산을 위한 수성가스전이반응에 적용가능성을 확인하기 위하여 Cu/ZnO/MgO/Al₂O₃ (CZMA) 촉매를 공침법을 사용하여 제조하였다. 제조된 촉매는 BET, H₂-TPR을 사용하여 분석되었다. 촉매의 반응성 테스트는 고농도의 CO를 포함하는 합성가스로부터 단일 Low Temperature Shift 반응을 거치는 경우와 High Temperature Shift 반응을 거친 후 스팀의 응축 없이 즉시 LTS 반응을 거치는 두 가지의 경우를 비교 및 분석하였다. 두 조건에서 steam/CO 비, 유량 및 유속, 온도에 따른 반응특성을 확인하였다. 전환된 저농도의 CO와 스팀이 응축 없이 LTS로 즉시 주입되는 경우 많은 양의 스팀이 존재함에도 불구하고 대부분의 조건에서 다소 낮은 CO 전환율을 나타냈다. 또한 steam/CO비, 온도 및 유속에 대한 영향이 크게 나타나 최적의 조업조건을 결정하기에 추가적인 분석이 요구되었다. 반면, 고농도의 CO 기체를 포함하는 조건에서는 탄소침적 또는 촉매의 활성 저하가 나타나지 않았으며 대부분의 조건에서 높은 CO 전환율을 나타내었다. 결론적으로 Cu/ZnO/MgO/Al₂O₃ 촉매를 적용하여 고농도의 CO를 포함하는 합성가스 조성에서 적절한 조업조건을 적용시키면 단일 LTS 반응을 적용해도 고농도의 CO를 CO₂로 충분히 전환 가능함을 확인하였다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.536-537
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• 2006

In the present work, the sintering behavior of high strength Al-5.6Zn-2.5Mg-1.6Cu (in wt.%) alloy compacts prepared from elemental powders was investigated. Microstructural evaluation was accompanied by XRD and DSC methods in order to determine the temperature and chemical composition of the liquid phases formed during sintering. It was found that three transient liquid phases are formed at 420, 439 and 450 $^{\circ}C$. Microstructural study revealed the progressive formation of sintered contacts due to the presence of the liquid phases, although the green compact expands as a result of the melt penetration along the grain boundaries. While Zn melts at ${\sim}420\;^{\circ}C$, the intermetallic phases formed between Al and Mg were found to be responsible for the formation of liquid phase and the dimensional change at higher temperatures.

• 한국재료학회지
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• 제7권8호
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• pp.660-667
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• 1997

AI-Mg-합금의 용융산화에 의해 생성되는 AlO$_{2}$O$_{3}$-복합재료의 미세구조에 미치는 합금원소의 영향을 연구하였다. AI-1Mg 합금과 AI-3Mg 합금을 기본으로하여 Si, Zn, Sn, Cu, Ni, Ca, Ce를 1, 3, 5 %를 무게비로 첨가하였다. 각 합금을 1473K에서 20시간 유지하여 산화시킨 후 산화층의 거시적 형상과 미세구조를 광학현미경으로 관찰하였다. 각 미세구조의 상분율을 상분석기로 측정하였다. 산화층의 최첨단면은 SEM과 EDX로 관찰하고 분석하였다. Cu나 Ni를 첨가한 합금으로부터 성장한 산화층의 미세구조가 가장 치밀하였다. Zn이 포함된 합금으로부터 성장한 산화층 최첨단 성장면에는 ZnO가 관찰되었다. Zn이 포함되지 않은 다른 합금의 성장 전면에는 항상 MgAi$_{2}$O$_{4}$상이 관찰되었다.

• Biotechnology and Bioprocess Engineering:BBE
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• 제2권2호
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• pp.126-131
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• 1997

The biosorption and desorption of Cr, Cu and Al were carried out using brown marine algae Sargassum fluitans biomass, known as the good biosorbent of heavy metals. The content of alginate bound to light metals could be changed by physical and chemical pretreatment. The maximum uptake of Cr, Cu and Al was independent of the alginate content. The maximum uptaker of Al was two times(mole basis) than those of Cu and Cr. The aluminum-alginate complex was found in the sorption solution of raw and protonated biomass. Most of Cu, Al and light metals sorbed in the biomass were eluted at pH 1.1. However, only 5 to 10% of Cr sorbed was eluted at pH 1.1. The stoiceometric ion exchange between Cu and Ca ion was observed on Cu biosorption with Ca-loaded biomass. A part of Cr ion was bound to biomass as Cr(OH)2+ or Cr(OH)2+. Al was also bound to biomass as multi-valence ion and interfered with the desorbed Ca ion. The behavior of raw S. fluitans in ten consecutive sorption-desorption cycles has been investigated in a packed bed flow-through-column during a continuous removal of copper from a 35 mg/L aqueous solution at pH 5. The eluant used was a 1%(w/v) CaCl2/HC solution at pH 3.

• 소성∙가공
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• 제13권1호
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• pp.53-58
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• 2004

The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment were investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) were hot extruded to make T-shape bars at extrusion temperature of $380^{\circ}C$, then the bars were solution treated at $480^{\circ}C$ for 2hrs followed by artificial aging at $120^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consisted of elongated grains, however, fine equiaxed grains were also observed around surface. The microstructural gradient suggested that different restoration process could proceed during the hot extrusion. For B1 and B2, different grain growth behaviors were found around the surface during the post heat treatment. Rapid grain growth behavior was observed for B1 around the surface, however, it was not observed for B2. Orientation pinning, which was related with the evolution of preferred orientation, and precipitation were thought to be responsible for the rapid grain growth.

• 대한금속재료학회지
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• 제50권9호
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• pp.669-675
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• 2012

Hot tearing was the most significant casting defect when the castability evaluation of the Al-Zn-Mg-Cu alloy system was conducted. It was related to the solidification range of the alloy. Therefore, the hot tear susceptibility of the AA7075 alloy, whose solidification range is the widest, was evaluated. The hot tear susceptibility was evaluated by using a mold for a hot tearing test designed to create the condition for the occurrence of hot tear in 8 steps. According to the tearing location and shape, a hot tear susceptibility index (HTS) score was measured. The solidification range of each alloy and hot tear susceptibility was compared and thereafter the microstructure of a near tear defect was observed. As a result, the HTS of the AA7075 alloy was found to be 67. Also, the HTS in relation to a change in Zn, Mg, Cu composition showed a difference of about 6-11% compared to the AA7075 alloy.

• 한국주조공학회지
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• 제39권3호
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• pp.33-43
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• 2019

In this study, the effects of Zn additions on the mechanical properties of Al-Si-Mg-Cu alloys were investigated by increasing the amount of Zn up to 8wt.%. As the Zn content was increased up to 6 wt.%, the yield strength and elongation changed linearly without any significant changes in the size and shape of the main reinforcement phase. However, it was confirmed by SEM observation that the Mg-Zn phase formed between the reinforcement phases when the amount of Zn added exceeded 7wt.%. A Mg-Zn intermetallic compound formed between the $Mg_2Si$ phase, becoming a crack initiation point under stress. Thus, the formation of the Mg-Zn phase may cause a sharp decrease in the elongation when Zn at levels exceeding 7 wt.%. It was also found that the matrix became more brittle with increasing the Zn content. From these results, it can be concluded that the formation of the Mg-Zn intermetallic compound and the brittle characteristics of the matrix are the main causes of the remarkable changes in the mechanical properties of this alloy system

• 한국주조공학회지
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• 제34권3호
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• pp.100-106
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• 2014

In recent years, Mg and its alloys have attracted a great deal of attention due to their low density, relatively excellent castability, and straightforward recyclability. Mg alloys have been widely applied to various industrial fields, and are representatively used in automotive and electronic parts. According to previous researches, the electrical conductivity of Mg alloys greatly decreases with increasing Al content. However, with the addition of Zn and/or Cu, the electrical conductivity of Mg alloys is maintained or slightly increased, and improved mechanical properties are obtained as well. On this basis, Mg-Zn-Cu alloys have been investigated in the present study with a focus on the effect of adding Zn and Cu on the electrical conductivity. The Zn and Cu contents ranged from 4 to 6wt.% and 0 to 1.5wt.%, respectively. Ternary Mg-Zn-Cu alloys have been prepared by gravity casting in a steel mold. In the as-casting condition, the electrical conductivity of Mg-Zn-Cu alloys showed a linear increasing trend with decreasing Zn and increasing Cu contents. Furthermore, impact values of Zn = -1.5 and Cu = 2.5 were determined for these alloys by electrical conductivity tests.

• Journal of Welding and Joining
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• 제18권2호
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• pp.213-213
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)