• 한국분말재료학회지
• /
• 제9권6호
• /
• pp.394-408
• /
• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• 전기화학회지
• /
• 제2권3호
• /
• pp.117-122
• /
• 1999

본 연구에서는 알칼리 용액에서 알루미늄의 부식속도를 측정하면서, 합금원소, 알칼리도(KOH농도),용액온도, 그리고 용액에 첨가하는 부식 억제제의 종류와 그 농도 등이 미치는 영향에 대해 조사하였다. 알루미늄 제품에 따라서는 순도 $99\%$ 이상인 AA-1050의 부식속도가 가장 낮은 반면에 Mg나 Mn이 포함된 합금은 상대적으로 높게 측정되었다. KOH 수용액에 ZnO를 포화농도로 첨가하면 부식속도가 $50\%$ 이상 억제되는 효과가 나타났지만. ZnAc는 부식 억제제로서 역할하지 못하였다. 알칼리도와 용액온도가 높을수록 ZnO의 부식 억제효과는 상승하였다 부식속도는 KOH농도에 대해 1차 선형 증가함수 그리고 온도 역수에 대해 지수형 감소함수로 나타났다. SEM과 EDS를 사용하여 부식 표면에 부착된 물질의 성분을 분석하였으며, XRD의 기기분석을 통하여 KOH 용액에서의 알루미늄의 부식 생성물이 $Al(OH)_3$임을 확인하였다.

• 한국주조공학회지
• /
• 제10권6호
• /
• pp.528-537
• /
• 1990

7XXX aluminum alloy powders produced by the self-manufactured rotating disc atomizer were investigated to determine the influence of the atomization parameters on the particle size distributions in air atmosphere. The particle size distributions are almost always bimodal with the dominant mode on the large particle size. Average powder size of 7XXX aluminum alloy is $74/{\mu}m~125/{\mu}m$ when melt is poured with the rate of 9g /sec at 730$^{\circ}C$ on a rotating disc of 30㎜ diameter at 6300rad/sec. The mass of finer particle increased when disc diameter, angular velocity, pouring temperature increased and pouring rate decreased. The powder shapes of bimodal change from acicular to tear-drop and from tear-drop to ligament with increasing powder size. Powder shape was determined by the atomization mechanism and oxidation in liquid state. Microstructure of powders appeared to be cell and cellular dendrite. The SDAS of Al-7.9wt%Zn-2.4wt%Mg-1.5wt%Cu-0.9wt%Ni Powders is $0.8{\mu}m~1.0{\mu}m$ for the powders of $size＋44{\mu}m~53{\mu}m$ and $1.6{\mu}m∼1.8{\mu}m$ for the powders of $size＋105{\mu}m~125{\mu}m$, repectively.

• 한국주조공학회지
• /
• 제32권5호
• /
• pp.231-240
• /
• 2012

In present study, the effect of heat treatment on the microstructure and mechanical properties of the gravity cast superchargers housing using A356 alloy were investigated. In order to identify the characteristics of superchagers housing casting with heat treatment, Vickers hardness test, electrical conductivity test, opical and scanning electron microscopy were performed. And also, to investigate their mechanical properties, the T6 treated superchagers housing casting in optimum heat treatment condition were carried out tensile test using UTM (Universal Testing Machine).

• Steel and Composite Structures
• /
• 제22권4호
• /
• pp.745-752
• /
• 2016

An investigation has been done to study the evolution of the microstructure, mechanical and electrical properties of AlMgSi alloy destined for the transport of electric energy, in function of the deformation caused by the cold drawing process. We identified that drawing of aluminum wire causes development of a fibrous texture of type <111> and <100>. We notice also that the electrical resistivity and mechanical resistance increases with the increasing of the deformation level. Characterization methods used in this work is: The Electron Back Scattered Diffraction EBSD, X-Ray diffraction, Vickers microhardness, Tensile test, Measuring electrical resistivity, the Scanning Electron Microscope (SEM) and Energy Diffraction Spectrum (EDS).

• 대한금속재료학회지
• /
• 제49권2호
• /
• pp.104-111
• /
• 2011

An ultrafine grained Mg-9Al-1Zn magnesium alloy with the mean grain size less than $1{\mu}m$ was produced by using high-ratio differential speed rolling. The processed alloy exhibited excellent superplasticity at relatively low temperatures. The micro-forming tests were carried out using a micro-forging apparatus with micro V-grooved shaped dies made of silicon and the micro-formability was evaluated by means of micro-formability index, $R_f$ ($=A_f/A_g$, $A_f$: formed and inflowed area into the V-groove, $A_g$: area of the V-groove). The $R_f$ value increased with temperature up to $280^{\circ}C$ and then decreased beyond $300^{\circ}C$. The decrease of the $R_f$ value at $300^{\circ}C$ was attributed to the accelerated grain coarsening. Increasing the micro-forging pressure increased the $R_f$ values. At a given die geometry, die filling ability decreased as the die position moved away from the die center to the end. FEM simulation predicted this behavior and a method of improving this problem was proposed.

• 소성∙가공
• /
• 제31권3호
• /
• pp.117-123
• /
• 2022

In this study, a commercial AZ61 magnesium alloy is extruded at 300 ℃ and 400 ℃ and the microstructures, mechanical properties, and high-cycle fatigue properties of the extruded materials are investigated. Both extruded materials have a fully recrystallized microstructure with no Mg₁₇Al₁₂ precipitates. The average grain size and maximum basal texture intensity of the extruded material increase with increasing extrusion temperature. The material extruded at 400 ℃ (AZ61-400) has higher tensile yield strength and lower compressive yield strength than the material extruded at 300 ℃ (AZ61-300) because of the stronger basal texture of the former. Because of coarser grain size, the tensile elongation of AZ61-400 is lower than that of AZ61-300. Despite the differences in microstructures and tensile/compressive properties, the two extruded materials have the same fatigue strength of 110 MPa. This is because the finer grain size of AZ61-300 causes an increase in fatigue strength, but its weaker texture causes a decrease in fatigue strength. In both extruded materials, fatigue cracks initiate at the surface of fatigue specimens at all stress amplitudes tested.

• 한국강구조학회 논문집
• /
• 제28권5호
• /
• pp.373-382
• /
• 2016

도장 또는 금속용사는 강구조물의 방식에 널리 사용되고 있으며, 금속용사와 도장의 복합방식법은 혹독한 부식환경하에 놓인 강구조물에 고내후성 피복방식법으로 적용되고 있다. 본 연구에서는 아연(Zn), 아연-알루미늄(ZnAl)합금, 알루미늄(Al), 알루미늄-마그네슘(AlMg)합금의 4종류 금속용사 후 실링 처리한 시편, 4종류 금속용사 후 중방식 도장한 시편과 도장만 실시한 시편을 대상으로 175일간의 ISO 20340 부식촉진실험을 실시하여, 각 방식법의 상대적인 내후성능을 비교, 검토하였다. 강재표면까지 도달하는 원형 및 선형 초기결함으로부터의 표면상태 변화 및 도막의 노화면적에 근거한 내후성능의 평가 결과, 금속용사 후 실링 처리한 시편의 경우에는 알루미늄(Al) 및 알루미늄-마그네슘(AlMg)금속용사 후 실링 처리한 시편이 가장 우수한 내후성능을 보였으며, 금속용사 후 도장을 실시한 금속용사와 도장의 복합방식법의 경우에는 아연(Zn)용사에 도장을 실시한 복합방식 시편이 가장 우수한 내후성능을 나타내었다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.217-217
• /
• 2012

플라즈마 전해산화(Plasma Electrolytic Oxidation)는 수용액 중에서 Al, Mg, Ti 등의 금속표면에 산화막을 형성시키는 기술로서, 기존의 양극산화법과 유사한 장치에서 고전압을 가해 미세플라즈마 방전을 유도하여 치밀한 산화막을 형성하는 표면처리 기술이다. 본 연구에서는 6061 알루미늄 합금의 대면적 시편을 이용하여 PEO공정으로 산화막을 형성시켰다. 산화막의 조성 및 미세구조는 XRD와 SEM, EDS를 이용하여 분석하였다. 형성된 산화막은 회색에서 밝은 회색으로 시편 전면에 고르게 나타났다. 피막 성장인자를 정교하게 조절함으로써 강한 피막 접착력과 낮은 표면조도를 가지는 매끈한 표면을 얻을 수 있었고, 그에 따른 물성 변화를 분석하였다. 또한 시편의 크기에 관계없이 동일한 조건에서 동일한 물성이 나오는 것으로 분석되었다. 이를 통해 균질한 대면적 피막의 높은 신뢰성을 요구하는 다양한 산업분야에 적합한 표면처리 방법으로서 PEO공정이 활용될 수 있음을 확인하였다.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 1992년도 추계학술발표강연 및 논문개요집
• /
• pp.14-14
• /
• 1992

During the past five years a very successful effort has been made to improve existing and develop new aluminium alloys. The progress achieved has been possible because of the development of new production methods, such as powder metallurgy and spray/deposition. These methods make use of rapid solidification process which alloys compositions other than those achieved by conventional ingot metallurgy. The ingot metallurgy of the 2000 and 7000 series used thus far, as well as the age hardening Al-Li alloys, show several disadvantages caused by the production process. Such problems are primarily coarse intermetallic constituent phases, coarse grains and macrosegregation, resulting in low fracture toughness. The present contribution reports results of an experimental investigation performed on a modern high strength spay deposited aluminium alloy of the Al-Zn-Mg-Cu (7075 and the modified 7150X) type. Results are given in terms of its microstructural characterization by using X-ray diffractomertry and transmission electron microscopic. The mechanical propierties of those alloys in the as-extruded and extruded+aged condition were evaluated by using microhardness Vickers, tensile test and fracture toughness measurements.