• 한국세라믹학회지
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• 제34권5호
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• pp.483-490
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• 1997

Al2O3/metal composites were fabricated by oxidation and reaction of molten Al-alloy into two types of commercial Al2O3-SiO2 fibrous insulation board. The growth rate, composition and microstructure of these materials were described. An AlZnMg(7075) alloy was selected as a parent alloy. Mixed polycrystalline fiber and glass phase fiber were used as a filler. The growth surface of an alloy was covered with and without SiO2. SiO2 powder was employed as a surface dopant to aid initial oxidation of Al-alloy. Al-alloy, SiO2, fiber block and growth inhibitor CaSiO3 were packed sequentially in a alumina crucible and oxidized in air at temperature range 90$0^{\circ}C$ to 120$0^{\circ}C$. The growth rate of composite layer was calculated by measuring the mass increasement(g) per unit surface($\textrm{cm}^2$). XRD and optical microscope were used to investigate the composition and phase of composites. The composite grown at 120$0^{\circ}C$ and with SiO2 dopant showed rapid growth rate. The growth behavior differed a little depending on the types of fiber used. The composites consist of $\alpha$-Al2O3, Al, Si and pore. The composite grown at 100$0^{\circ}C$ exhibited better microstructure compared to that grown at 120$0^{\circ}C$.

• 한국분말재료학회지
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• 제26권1호
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• pp.22-27
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• 2019

In this study, the effects of powder size and composition on the reflectance of Al-Si based alloys are presented. First, the reflectance of Al-Si bulk and powder are analyzed to confirm the effect of powder size. Results show that the bulk has a higher reflectance than that of powder because the bulk has lower surface defects. In addition, the larger the particle size, the higher is the reflectance because the interparticle space decreases. Second, the effect of composition on the reflectance by the changing composition of Al-Si-Mg is confirmed. Consequently, the reflectance of the alloy decreases with the addition of Si and Mg because dendrite Si and $Mg_2Si$ are formed, and these have lower reflectance than pure Al. Finally, the reflectance of the alloy is due to the scattering of free electrons, which is closely related to electrical conductivity. Measurements of the electrical conductivity based on the composition of the Al-Si-Mg alloy confirm the same tendency as the reflectance.

• 열처리공학회지
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• 제4권1호
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• pp.37-41
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• 1991

In this study, the effect of solution treatment temperature on the tensile property in intermediate thermo-mechanical treated Al-Li alloys are investigated. After the intermediate thermo-mechanical treated Al-Li, Al-Li-Mg and Al-Li-Mg-Zr alloys were solution treated at various temperatures (500, 520 and $540^{\circ}C$), these were aged at $190^{\circ}C$, $240^{\circ}C$ and tested tensile properties. The results obtained from the experiment are as follows ; 1) The optimum solution heat-treatment temperature is $540^{\circ}C$ for a Al-Li alloy, and the recrystallized grain size is about $70{\mu}m$. 2) The optimum solution heat-treatment temperature is $500^{\circ}C$ for a Al-Li-Mg alloy, and the recrystallized grain size is the most coarse in all alloys. 3) The tensile property is independent of the solution treatment temperature in a Al-Li-Mg-Zr alloy, and the recrystallized grain size is the finest owing to addition of Zr.

• 소성∙가공
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• 제28권6호
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• pp.361-367
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• 2019

Microstructure evolution and tensile properties of Al-8mass%Mg alloy casting billet by biaxial alternative forging were investigated in this study. An alternative forging system tailored in this study was used to allow continuous strain accumulations on the alloy workpiece. A finite element (FE) simulation results revealed that the strain was mainly concentrated in the core and that the shear bands developed into a form with an X shape in the cross-section of workpiece after the alternative forging using octangular rod shaped dies. With increasing the forging passes, it was observed that the Al-8mass%Mg alloy workpieces were significantly deformed, and cracks began to form and propagate on the both ends of the forged workpieces after five passes at room temperature. In as-forged microstructures taken by microscopes, twins, clustering of dislocations, and fine subgrains were found. Tensile strengths of the forged specimens showed significant increases depending on the number of forging passes, and a trade-off relationship was observed between the elongation and strength. At room temperature and 100℃ the workpieces showed similar behaviors in microstructural evolution and tensile properties depending on forging passes, while the increase range in strength was reduced at 200℃.

• Corrosion Science and Technology
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• 제9권6호
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• pp.233-238
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• 2010

Hot-dipped Al-Mg-Si coatings to alternate Zn and Zn alloy coatings for steel were examined on metallographic structure, corrosion resistance, sacrificial ability, formation and growth of inter-metallic compounds, and mechanical properties. Near the eutectic composition of quasi-binary system of Al-$Mg_2Si$, very fine eutectic structure of ${\alpha}$-Al and $Mg_2Si$ was obtained and it showed excellent corrosion resistivity and sacrificial ability for a steel in sodium chloride solutions. Formation and growth of Al-Fe inter-metallic compounds at the interface of substrate steel and coated layer was suppressed by addition of Si. The inter-metallic compounds layer was usually brittle, however, the coating layer did not peel off as long as the thickness of the inter-metallic compounds layer was small enough. During sacrificial protection of a steel, amount of hydrogen into the steel was more than ten times smaller than that of Zn coated steel, suggesting to prevent hydrogen embrittlement. Al-Mg-Si coating is expected to apply for several kinds of high strength steels.

• 한국주조공학회지
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• 제37권4호
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• pp.101-107
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• 2017

This study investigated the effect of Pd on the microstructure, tensile and creep properties of Mg-4Al-2Sn (AT42) alloy at a high temperature for transportation-related industrial applications. AT42-xPd (x = 0, 1 and 2 wt. %) alloys were prepared using a permanent mould casting method. The microstructures of the as-cast alloys were characterized by the presence of the intermetallic phases $Mg_{17}Al_{12}$, $Mg_2Sn$ and $Al_4Pd$. The addition of Pd was found to improve the tensile properties of AT42 at room and at elevated temperatures, and to increase the creep resistance at elevated temperatures. A small amount of Pd could markedly improve the tensile properties of AT42 by means of grain-refinement and the dispersion of secondary phase strengthening. Moreover, the thermally stable phase $Al_4Pd$ effectively improves the creep resistance of AT42 due to the strengthened grain boundaries and the suppressed formation of $Mg_{17}Al_{12}$.

• 한국표면공학회지
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• 제41권3호
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• pp.109-113
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• 2008

High strength 7xxx series Al-Zn-Mg alloy have been investigated for using light weight automotive parts especially for bump back beam. The composition of commercial 7xxx aluminum has the Zn/Mg ratio about 3 and Cu over 2 wt%, but this composition isn't adequate for appling to automotive bump back beam due to its high resistance to extrusion and bad weldability. In this study the Zn/Mg ratio was increased for better extrusion and Cu content was reduced for better welding. With this new composition we investigated the effect of composition on the resistivity against stress corrosion cracking. As the Zn/Mg ratio is increased fracture energy obtained by slow strain rate test was decreased, which means degradation of SCC resistance. While the fracture energy was increased with Cu contents although it is below 1%, which means improvement of SCC resistance. These effects of composition change on the SCC resistivity were identified by observing the fracture surface and crack propagation.

• 열처리공학회지
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• 제22권4호
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• pp.217-222
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• 2009

The effects of severe plastic deformation by equal channel angular pressing (ECAP) and subsequent heat treatment on the low cycle fatigue behaviors of Al-Mg-Si alloy were investigated. The specimens which were peak aged at $175^{\circ}C$ after solution treatment showed cyclic hardening at all strain amplitudes, while the specimens ECAPed after solution treatment showed cyclic softening at all strain amplitudes during fatigue. The specimens aged at $100^{\circ}C$ after ECAP showed slight cyclic hardening. Various changes of cyclic fatigue behavior after severe plastic deformation and/or heat treatment were discussed in terms of the microstructural changes and precipitation conditions.

• 한국주조공학회지
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• 제41권1호
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• pp.3-10
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• 2021

알루미늄 합금과 주철의 복합주조 공정 중에는 주철로부터 철 성분이 용해되어 알루미늄 용탕에 혼입될 수 있으므로 다양한 Fe함유 금속간 화합물이 형성되며, 이로 인해 알루미늄 합금의 인장 특성이 크게 저하 될 수 있다. 반면 불순물로 첨가되는 Fe와 는 달리 Cu의 경우 알루미늄 합금의 기계적 물성을 향상시키기 위해 첨가되는 합금원소이다. 본 연구에서는 Fe와 Cu의 첨가로 인한 알루미늄 합금의 미세조직 및 인장특성의 변화를 조사하였다. 첨가된 Fe 함량이 1% 이상일 경우 조대한 Al₅FeSi 상과 같은 Fe 함유 화합물들이 다량 형성되어 인장 특성이 현저히 감소하는 것으로 나타났다. Cu가 첨가 된 알루미늄 합금의 경우 Al2Cu 상이 추가로 형성되었으며, 인장 강도가 뚜렷하게 향상되는 결과를 보였다.

• 열처리공학회지
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• 제32권6호
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• pp.249-255
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• 2019

This study is intended to clarify the main microstructural factors that contribute to an increase of hardness during isothermal aging in Mg-Al alloy. For this work, Mg-9.3%Al alloy specimens were solution-treated at 688 K for 24 h followed by water quenching, and then aged at 473 K for up to 24 h. The aging at 473 K yielded nodular discontinuous precipitates (DPs) with (${\alpha}+{\beta}$) lamellar morphology at the grain boundaries, and the volume fraction of DPs increased from 0% to ~30% with increasing aging time up to 12 h. For the aging times longer than 12 h, further formation of DPs was substantially inhibited owing to the occurrence of significant continuous precipitation within the ${\alpha}-(Mg)$ matrix, and the density of continuous precipitates (CPs) becomes greater with increasing aging time. Hardness of the specimen was steadily increased with aging time up to 24 h. Microstructural examination on the aged specimens revealed that the increased overall hardness at the early stage of aging is associated with the increased volume fraction of DPs, but at the later stage of aging, where the amount of DPs was hardly changed, the increased hardness of the ${\alpha}-(Mg)$ matrix in response to the higher density of CPs within the matrix, plays a key role in increasing the overall hardness value.