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High Temperature Deformation Flow Of A ZK60A Magnesium Alloy After Extrusion

Kawasaki M., Lee H. J., Oh M. C., Ahn B.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1327--1330

EN

Flow behavior of a ZK60A magnesium alloy after continuous casting and subsequent extrusion was examined in tension at a range of strain rates of 3.0×10-6 − 1.0×10-2 s-1 at temperatures of 473-623K. The results demonstrated that the alloy exhibited a maximum elongation of ~250% at 523K when tested at an initial strain rate of 1.0×10-5 s-1 and strain rate sensitivity, m, of ~0.3-0.4 and the activation energy of ~94 kJ/mol were calculated under the testing conditions. The detailed investigation suggested that the high temperature flow of the ZK60A alloy having submicrometer grains demonstrates quasi-superplastic flow behavior controlled by a dislocation viscous glide process.

2

Evolution Of Precipitate Morphology During Extrusion In Mg ZK60A Alloy

Park J., Jung K. H., Lee G. A., Kawasaki M., Ahn B.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1423--1426

EN

In this study, a continuously casted ZK60A magnesium alloy (Mg-Zn-Zr) was extruded in two different extrusion ratios, 6:1 and 10:1. The evolution of precipitates was investigated on the two extruded materials and compared with that of as-casted material. The microstructural analysis was performed by electron backscatter diffraction and transmission electron microscopy, and the compositional information was obtained using energy-dispersive X-ray spectroscopy. Several distinct morphologies of precipitates were observed, such as dot, rod, and disk shaped. The formation mechanisms of those precipitates were discussed with respect to the heat and strain during the extrusion process.

3

Magnetization and structure of Fe-Al powders.

Fujii M., Saito K., Wakayama K., Kawasaki M., Yoshioka T., Isshiki T., Nishio K., Shiojiri M.

Inżynieria Materiałowa

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1998

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R. XIX, nr 4

860-863

EN

A few micrometers-sized Fe1-xAlx (x=0.35-0.42) powders prepared by atomizing method have the B2 structure and are paramegnetic. The powder milled for several hours is magnetized and has a spontaneous magnetization as great as 100 emu/g. The milled powder particles become flakes, which are composed of lamellae expanding parallel to the (110) plane and having heavily distorted lattice. High-resolution transmission electron microscopy and electron diffraction revealed that structures appear in very thin areas within the lamellae. These superlattices indicate the creation of large number of antiphase boundaries, which induce ferromagnetism. When the milled powder is heated at 100-400 degrees centigrade the magnetization decreases to a few tens emu/g, the lamella structures being kept.

4

New specimen preparation methods for materials transmission electron microscopy using ion-milling

Kawasaki M., Yoshioka T., Shiojiri M.

Electron Technology

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1998

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Vol. 31, No. 2

183-188

EN

Three mew preparation methods of specimen for transmission electron microscopy (TEM) applicable to materials characterization have developed using ion milling. One is an ion-digging method, where diamond powder particles are dispersed on the surface of specimen such as multilayer heterostructure and then the specimen are bombarded gy Ar ions perpendicular to its surface. Narrow poles with a diamond particle at the top form by ion digging, and can be observed in the surface profile by TEM. This method does not need the adhesion of two sliced substances and the mechanical polishing, which are troublesome pre-treatments used in conventional method. The others are preparation methods of selactions of powder particles, using photo-resistor Ni(P) elestroless plating for embedding the particles. These methods allow high-resolution TEM observations of micrometr-sized particles.