Aluminum based metal matrix composite reinforced with SiC particles was fabricated by the powder-in sheath rolling method. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1mm was used as a sheath. Mixture of aluminum powder and SiC particles of which volume content was varied from 5 to 20vol.% was filled in the tube by tap filling and then rolled to 75% reduction at ambient temperature. The rolled specimen was sintered at 56 for 0.5hr. The tensile strength of the (SiC)/Al composite increased with the volume content of SiC particles, and at 20vol.% it reached a maximum of 100㎫ which is 1.6 times higher than unreinforced material. The elongation decreased with the volume content of O particles. The mechanical properties of the (SiC)/Al composite fabricated by the powder-in sheath rolling is compared with that of (AlO)/Al composite by the same process.ess.

In this paper processing and mechanical properties of Al-20 wt％ Si alloy was studied. A bulk form of Al-20Si alloy was prepared by gas atomizing powders having the powder size of 106-145 and powder extrusion. The powder extrudate was subsequently equal channel angular pressed up to 8 passes in order to refine grain and Si particle. The microstructure of the gas atomized powders, powder extrudates and equal channel angular pressed samples were investigated using a scanning electron microscope and X-ray diffraction. The mechanical properties of the bulk sample were measured by compressive tests and a micro Victors hardness test. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength and hardness of the Al-2OSi alloy without deteriorating ductility in the range of experimental strain of 30％.

The study for producing the flake powders by milling of aluminum foil and gas atomized powders was carried out. The effects of lifter bars on the ball motions and milling of aluminum foils were also investigated. The aluminum foils were laminated each other, elongated, fragmented into small foils and finally formed into the flake powders during the dry ball-milling. The spherical atomized-powders were milled to coarse flake powders with high aspect ratio and then changed to fine flake powders with lower aspect ratio. Even though long times were required for making flake powders by milling of foils, the water covering areas of them were higher than those of powders milled using gas-atomized powders, suggesting aluminum foils were more plastically deformed by micro-forging. On the other hand, as the number of lifter bars increased, the necessary rotation speeds of milling jar for cascading mode and cataracting mode decreased drastically. It was possible to achieve same quality of milled flake powder by using the lifter bars under the lower milling speeds. The painting test showed that the appearance of painted surface was good and optimum content range of aluminum paste in car paint to maximize the degree of gloss was 3-5%.

We report on the formation and chemical leaching of non-equilibrium alloy produced by rod milling. X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry, scanning electron microscopy, and vibrating sample magnetometry were used to characterize the as-milled and leached specimens. After 400 h, only the peak of the body-centered cubic type was present in the XRD pattern. The entire rod milling process could be divided into three different stages of milling: agglomeration, disintegration, and homogenization. The saturation magnetization, decreased with increased milling time, the of the powders before milling was about 113.8 emu/g, the after milling for 400 h was about 11.55 emu/g. Leaching of the Al in KOH of the Al at room temperature from the as-milled powders did not induce any significant change in the diffraction pattern. After the leached specimen had been annealed at for 1 hour, the nanoscale crystalline phases were transformed into the bcc Fe, cubic Co, and phases. On cooling the specimen from 85, the degree of magnetization increased slightly, then increased sharply at approximately 364.8, indicating that the bcc phase had been transformed to the Fe and Co phases.

The composites fabricated by powder in sheath rolling method were cold-rolled by 50% reduction and annealed for 1.8 ks at various temperatures ranging from 200 to 50, for improvement of the mechanical properties. The mechanical properties and texture of the composites after rolling and annealing were investigated. The tensile strength of the composites increased significantly due to work hardening after cold rolling, however it decreased due to restoration after annealing. The strength of the composites was improved by thermo mechanical treatment. On the other hand, the texture evolution with annealing temperatures wa,i different between the unreinforced material and the composites. The unreinforced material showed a deformation (rolling) texture of which main component is ｛112｝<111> at annealing temperatures up to 30. However, the composites have already exhibited a recrystallization texture of which main component is ｛001｝<100> after annealing at 20. This proves that the critical temperature for recrystailization is lower in the composites than in the unreinforced ones.

Aluminum-based composites were fabricated by a powder-in sheath rolling method. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. A mixture of aluminum powder and particles of which volume content was varied from 5 to 20%, was filled in the tube by tap filling and then rolled by 75% reduction in thickness at ambient temperature. The rolled specimen was then sintered at 56 for 0.5 h. The mixture of Al powders and particles was successfully consolidated by the sheath rolling. The composite fabricated by the sheath rolling showed a recrystallized structure, while unreinforced Al powder compact fabricated by the same procedure showed a deformed structure. The unreinforced Al powder compact was characterized by a deformation (rolling) texture of which main component is {112}<111>, while the composite showed a mixed texture oi deformation and recrystallization. The sintering resulted in recrystallization in Al powder compact and grain growth in the composite.

The powder-in sheath rolling was applied to the fabrication of composite. A stainless steel tube with outer diameter of 12 mm and wall thickness of 1 mm was used as a sheath. Mixture of aluminum powder and particles of which volume content was varied from 5 to 20 vol.% was filled in the tube by tap filling and then rolled to 75% reduction at ambient temperature. The re]]ed specimen was sintered at 56 for 0.5 hr. The composite fabricated by the sheath rolling and subsequent sintering showed the relative density higher than 0.96. The tensile strength of the composite increased with the volume content of particles, and it reached a maximum of 90 MPa which is 1.5 times higher than unreinforced material. The elongation decreased with the volume content of particles. It is concluded that the powder-in sheath rolling is an effective method for fabrication of composite.

Al-l4wt.%Ni-l4wt.% Mm(Mm=misch metal) alloy powders rapidly solidified by the gas atomization method were subjected to mechanical milling(MM). The morphology, microstructure and hardness of the powders were investigated as a function of milling time using scanning electron microscopy(SEM), transmission electron microscopy(TEM) and Vickers microhardness tester. Microstructural evolution in gas-atomized Al-l4wt.%Ni-l4wt.% Mm(Mm=misch metal) alloy powders was studied during mechanical milling. It was noted that the as-solidified particle size of decreases during the first 48 hours and then increases up to 72 hours of milling due to cold bonding and subsequently there was continuous refinement to on milling to 200 hours. Two microstructurally different zones, Zone A, which is fine microstructure area and Zone B, which has the structure of the as-solidified powder, were observed. The average thickness of the Zone A layer increased from about 10 to in the powder milled for 24 hours. Increasing the milling time to 72 hours resulted in the formation of a thicker and more uniform Zone A layer, whose thickness increased to about . The TEM micrograph of ball milled powder for 200 hours shows formation of nano-particles, less than 20 nm in size, embedded in an Al matrix.

We report the structure, thermal and magnetic properties of a non-equilibrium alloy powder produced by rod milling and chemical leaching. An X-ray diffractometry(XRD), a transmission electron microscope(TEM), a differential scanning calorimeter(DSC), a vibrating sample magnetometer(VSM), and superconducting quantum interference device(SQUID) were utilized to characterize the as-milled and leaching specimens. The crystallite size reached a value of about 8.82 nm. In the DSC experiment, the peak temperatures and crystallization temperatures decreased with increasing milling time. The activation energy of crystallization is 200.5 kJ/mole for as-milled alloy powder. The intensities of the XRD peaks of as-milled powders associated with the bcc type structure formative at sharply increase with increasing annealing temperature. Above , peaks alloted to and are observed. After annealing at for 1h, the leached Ll specimen transformed into bcc -Fe and fcc Cu phases, accompanied by a change in the structural and magnetic properties. The saturation magnetization decreased with increasing milling time, and a value of about 8.42 emu/g was reached at 500 h of milling. The coercivity reached a maximum value of about 142.7 Oe after 500 h of milling. The magnetization of leached specimens as function of fields were higher at 5 K, and increased more sharply at 5 K than at 100 K.

The 6061 Al alloy based composites reinforced with 10 vol% SiC whiskers were prepared by powder metallurgy with the powders having the different sizes, i.e. < and> The composites were subjected to equal channel angular pressing (ECAP) at various conditions and the microstructural changes during ECAP were examined In the composites SiC whiskers were clustered and randomly aligned. The clusters were relatively well distributed in the composite with the smaller initial powder size. After ECAP, the clusters were aligned parallel to flow direction and became smaller. In addition, the shape of clusters was changed from irregular to round. The microstructure of the ECAPed samples were compared with those of the conventionally hot-extruded composites. The uniform microstructure and enhanced microhardness could be obtained by using the powders having the smaller size, decreasing ECAP temperature and repeating ECAP.

본 연구에서는 MA 방법을 사용하여 Al3Nb 금속간화합물의 조성에 Zr을 첨가하여 Al3(Nb1-x )Zrx 합금분말을 제조한 후 이에 따른 상변화 거동 및 미세구조특성을 분석하였다. MA는Al3(Nb1-x )Zrx의 조성으로 Al, Nb, Zr 원료분말과 arc meltinly된 Al3Nb, Al3Zr 금속간화합물 분말을 사용하여 300rpm의 회전속도로 20시간 동안 MA하였다. 이때의 정상상태의 원료분말은 약 4μm의 평균입도와 약 12~18nm의 결정립크기를 가졌으며, arc melting된 분말은 약 2μm의 평균입도와 약 14nm의 결정립크기를 가지는 분말을 얻을 수 있었다 원료분말과 금속간화합물 분말의 MA 기구는 상이한 거동을 나타내었으며, 분말의 내부변형량은 원료분말이 금속간화합 분말보다 내부변형량이 더 많이 축적되었다. 이는 원료분말의 MA 경우 냉간 압접과 파괴가 반복적으로 진행되었지만 금속간화합물 분말은 취약한 화합물상이어서 냉간압접 보다는 파괴가 지배적으로 진행되었기 때문이다. 원료분말을 MA하였을 경우에는 Al (Nb.Zr)2상이 형성되었으나 금속간화합물 분말로 MA하였을 경우에는 3원계 화합물상이나 비정질상으로 상변태 되지 않고 단지 두 합금상이 분쇄되어 나노복합화 되었다. 후속 열처리에 의해 원료분말인 경우에는 Al3(Nb.Zr)의 화합물상이 쉽게 형성되었으나, 금속간화합물 분말의 경우에는 새로운 상 생성은 얼었고 단지 열처리 전의 분말내부에 쌓여있던 내부변형에너지가 약 60% 정도 감소하였다.감소하였다.

Mechanically-alloyed NiAl powder and ball-milled (Ni+Al) powder mixture were sintered by spark-plasma sintering(SPS) process. Mechanical alloying was performed in a horizontal attritor for 20 h with rotation speed of 600 rpm. (Ni+Al) powder mixtures were prepared by ball milling for 1 and 10 h with 120 rpm. Both powders were sintered at for 5 min under torr vacuum with 50 MPa die pressure in a SPS facility. Sintered densities of 97% and 99% were obtained from mechanically-alloyed NiAl powder and (Ni+Al) powder mixture, respectively. The sintered compact of (Ni+Al) powder mixture showed large grain size by a very rapid grain growth, while the grain size of mechanically-alloyed NiAl powder compact after sintering was extremely fine(80 nm). The difference in densification behavior of both powders were discussed.