Materials Science Forum Vols. 654-656

Abstract: Texture distribution through thickness in 6xxx aluminum alloy cross-roll rolled sheet has been investigated using the electron back-scattered diffraction (EBSD) technique. Analyses of texture in three layers from the surface to the center of the sheet were performed. Near the surface, shear type textures including {012}<142> orientation and {112}<110> orientation were found and β-fiber texture were dominating. In the center layer, very weak β-fiber texture {112}<111> orientation, {123}<634> and {011}<211> were found with Cube, Cube-ND and Goss orientation plus others.

Abstract: In recent years, reducing carbon dioxide is being demanded in terms of preventing global warming. Lightening autobodies is one of the most practical ways to conduct it, for which converting the body sheets from conventional steel to Al-Mg-Si alloy is effective. Although the Al-Mg-Si alloys have the advantage that they have hardenability during paint baking and do not cause stretcher strain patterns, poor formability is a crucial drawback. Bendability is one of the most important properties related to formability. However, there has been no assessing method having both speediness and quantitative reproducibility. In this study, we have developed a assessing method based on the electric resistance decrease arising from the decrease in conducting section when cracks are formed by bending. Bendability was assessed by electrical resistance change as well as by crack density on the tension surface measured with an SEM. It was found that the new method have far greater speediness with the same quantitative reproducibility than the crack measurement method.

Abstract: In automobiles, a suspension bush, a set of aluminum parts connected to each other via rubber, is mounted into the suspension members to link the body to the wheels, and realizes hard and soft mounts contributing both to the stabilization during high speed driving and to absorbing the shock from the road. However, decohesion of the aluminum part from the rubber occurs occasionally, arising from the interface corrosion of aluminum, which deteriorates the performance of the vehicle directly. In this study, effects of alloy composition and processing route on this kind of corrosion will be investigated. Also, development of a new corrosion test that shortens the time for the test will be attempted.

Abstract: Porous copper with elongated cylindrical pores were fabricated by a unidirectional solidification method in a mixture of hydrogen and argon with high pressures. The porous copper with longitudinal pores and radial pores were compared on structure. The effect of both hydrogen pressure and argon pressure on structure of the porous copper including pore size, pore density, and porosity was investigated. The reason for the effect is explained.

Abstract: Street lighting system is an essential structure for the safety of traffic. Most of the lighting pole is made of steel and it is vulnerable to corrosion due to its hazardous surrounding environment. To mitigate such corrosion problems, stainless steel and iron steel are usually adopted, but they are also usually manufactured by hand, so it is not economical. Therefore, to overcome such problems new type FRP lighting pole is proposed. In recent years, FRP materials in the construction market are popularly utilized as an alternative for conventional construction materials. FRP material is known to have many advantages such as high chemical resistance, electro-magnetic transparency, high specific strength and stiffness, etc. In this paper, structural behavior of FRP lighting pole is compared with that of conventional lighting pole structures and we proposed the cross-section configuration of the FRP lighting pole with details on the manufacturing procedure.

Abstract: Molecular dynamics (MD) simulations based on a plastic crystal model (PCM) were performed for a Pd0.4Ni0.4P0.2 alloy in Metal-Metalloid (M-MLD) type of bulk metallic glass (BMG). Two kinds of clusters of cubeoctahedron capped with four half-octahedra and trigonal prism were used as initial atomic arrangements of the Pd0.4Ni0.4P0.2 alloy. Random rotations of clusters around their centers of gravity and subsequent structural relaxation vitrified the alloy. The high glass-forming ability of the Pd0.4Ni0.4P0.2 alloy is due to the critically-percolated, cluster-packed structure that is a universal feature for both M-MLD and M-M types of BMGs.

Abstract: A new series of bulk metallic glasses were developed by addition of Fe into the ternary Zr60Cu30Al10 alloy. Although Fe-Cu element pair shows distinct immiscibility with a large positive heat of mixing, substitution of Fe for Cu significantly improves the glass-forming ability of the ternary Zr60Cu30Al10 alloy. The critical diameter for glass-formation increases from 8 mm for Zr60Cu30Al10 alloy to 20 mm for Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys. As compared with the ternary Zr60Cu30Al10 alloy, the new quaternary Zr-Cu-Fe-Al alloys show lower liquidus temperatures. The Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys, the best BMG-formers in this alloy system, are found to locate very near a Zr-Cu-Fe-Al eutectic point. The new Zr-Fe-Cu-Al bulk metallic glasses exhibit high strength of about 1700 MPa. The plastic strain increases from 7.8% to 11.3% with increasing the content of Fe from 0 to 12.5%. The finding of a Ni-free Zr-based bulk glassy alloy with the extremely high glass-forming ability is expected to extend the future application of bulk metallic glasses.

Abstract: Viscous flow behaviour of supercooled liquids and mechanical properties in Zr55+XCu30-XNi5Al10 (X=0, 5 and 10 at. %) and Zr65Cu18Ni7Al10 bulk metallic glasses (BMGs) have been examined. Viscosity has been measured by using a penetration viscometer at a high-speed heating rate of 400 K/min. With increasing Zr-content, Tg tended to decrease and Tx tended to increase, resulting Tx (=Tx-Tg) increaseing up to about 170 K under a heating rate of 400 K/min by the DSC analysis. The viscosity lowered about one order of magnitude, e.g., minimum value of the viscosity decreased from 3~4x106 Pa-s for the Zr55Cu30Ni5Al10 and Zr60Cu25Ni5Al10 BMGs down to 5~6x105 Pa-s for the Zr65Cu20Ni5Al10 and Zr65Cu18Ni7Al10 BMGs under the same heating condition. Compression tests were also carried out at a slow strain rate of about 1 x 10-4 s-1 at room temperature. With increasing Zr-content, the apparent yield stress was decreased but the total strain at fracture was increased significantly, suggesting that there is a strong relationship between viscosity and the mechanical properties in these BMGs.

Abstract: Mechanical treatments such as deep rolling are known to affect the strength and toughness of metallic glass due to the residual stress. It is well known that compressive residual stress states usually enhance the mechanical properties in conventional metallic materials. We present investigations on the change of fracture behavior related with mechanical properties of “brittle” bulk metallic glass by cold rolling at room temperature. Improvement of the intrinsic plasticity is observed not only after constrained cyclic compression but also after cold rolling. Moreover, neither nanocrystallization nor phase separation occurs during deformation. By these findings we provide a unique fundamental basis by considering the introduction of structural inhomogeneity and ductility improvement in metallic glasses. The experimental evidence clearly supports that such an inhomogeneous glassy can be produced by residual stress in well known “brittle” bulk metallic glasses, and does not depend on a specific pinpointed chemical composition.

Abstract: Gas-atomized Cu-based metallic glass powder was heat-treated in air from below its glass transition temperature (Tg) to well above its crystallization temperature (Tx). Severe oxidation occurred at temperatures > Tx while at temperatures < Tg oxidation was sluggish. The oxidation products were determined and the mechanism is discussed based on the microstructural findings.