Papers by Author: Nobuhide Itoh

Abstract: Lifetime of tungsten electrodes for fusing was investigated in relation to their microstructure. Tungsten electrodes with two types of microstructures (recrystallized equi-axed and unrecrystallized fibrous) were subjected to repeated welding tests where work material was a tough pitch copper. Surface appearance of the electrodes after the test was observed with an SEM. Circumferential edge cracks were observed in the equi-axed electrode, which were presumed to be initiated by plastic flow of the work material. Although cracks were formed in the center of both types of electrodes, the total length of them is longer in the equi-axed electrode. Therefore, the lifetime was expected to be longer in the fibrous electrode than the equi-axed.

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: 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: Aluminum alloy is one of the candidates for the liners of compressed hydrogen tank mounted to fuel cell vehicles. It is crucial to elucidate the behavior of hydrogen in the alloy sheet with one side being exposed to hydrogen gas. In the present work, using the hydrogen microprint technique, in 6061 and 7075 aluminum alloy sheets, relationship between hydrogen pressure and the molar quantity of hydrogen emitted from the inside has been investigated. Under any pressure, the quantity of emitted hydrogen is about 10 times smaller in the 7075 alloy than in the 6061 alloy. This indicates that the amount of hydrogen atoms accumulating in the 7075 alloy may be much larger than that in the 6061 alloy.