Papers by Author: Naobumi Saito

Abstract: AZCa912, 8.8mass%Al-0.68mass%Zn-0.25mass%Mn-1.9mass%Ca-Bal.Mg, continuous casting bars were formed and their hot compression properties were measured. AZCa912 alloy is a noncombustible magnesium alloy. AZCa912 bars 50 mm in diameter were formed by a direct chill continuous casting method. The surfaces of the bars had excellent metallic luster. Grain sizes in the bars were 148, and the dendrite arm spacing was 16.9 μm. Cracks on the side surfaces of the samples were formed by compression at 250-300°C, 0.01-1/s and 350°C, 1/s. However, inner cracks were not observed and-5 μm fine-grains were formed. Some samples had an unchanged casting structure after hot pressing, and the percent of the structure remaining unchanged decreased with low-temperature compression.

Abstract: Grain refinements during hot compression of continuous casting AZ80 alloy bars and extrusive AZ61, AZ80 alloy bars were observed. The hot compression true stress-true strain curves of extrusive AZ61 and AZ80 alloy had similar tendencies, which were that the true stress increased and had a peak around 0.2 true strain, and then the stress decreased and was almost even from about 0.4 true strain. The stress peaks shifted to the high strain side as the compression speed, true strain speed, increased. However, the stress peaks did not shift at different compression temperatures. Fine grains were obtained under the condition of high strain speed and low temperature, but the grain sizes were uneven at low temperature compression. The stress peaks in the hot compression true stress-true strain curves of continuous casting AZ80 did not shift at different compression temperatures. AZ80 forging products with fine grains are expected to be formed under various conditions by using continuous casting AZ80.

Abstract: A new ECAP process method called rotary-die ECAP (RD-ECAP) was developed to form fine-grained bulk materials such as aluminium alloys, magnesium alloys, aluminium composites, and titanium, all of which can be processed under conditions of 573-773K, at an approximately 0.9-2.4 mm/s punch speed of 300MPa or lower. By the RD-ECAP method, ECAP processing of up to 2 passes can be done without sample removal and samples processed over 30 cycles were obtained.

Abstract: The AZ61 magnesium alloy was subjected to the differential speed rolling at different rolling conditions including reduction per pass, rotation speed ratio and rolling temperature, and the influences of the rolling conditions on microstructure, texture, mechanical properties and formability of the as-rolled sheets were investigated. Increasing the reduction per pass results in a more homogeneous microstructure and a relatively weaker basal texture. With increasing the rotation speed ratio, the inclination angle of basal pole toward the rolling direction increases and the stretch formability enhances correspondingly. Increasing the rolling temperature has an effect on weakening the basal texture intensity and leads to the enhancement of stretch formability.

Abstract: Titanium oxide/ titanium/ plastic composite implants were formed by coating commercially pure titanium thin films on the surfaces of plastic cylinders by DC magnetron sputtering method. The composite is uniformly formed and the surface of the composite implant is smooth. The implants in rat tibias were not broken and the films on the surfaces of the samples did not decompose. The samples with bone were able to cut by diamond knife and observations between bone and titanium oxide on titanium by TEM succeeded. Therefore, the composite is useful for implants or observations the interactions between titanium oxide and bone in detail.

Abstract: It was reported that the cold and warm press formability of the magnesium alloy was improved by the application of a differential speed rolling (DSR). However, it can be considered that the microstructure and the texture of the DSR processed sheets greatly change with the rolling conditions. In this study, commercial AZ31B magnesium alloy extrusions were processed by DSR at a differential speed ratio of 1.167 and a reduction per pass of 10% or less, and the effects of the rolling temperature, the number of rolling passes and reversal of the rolling direction on texture and mechanical properties were examined. As a result, it was found that the optimal rolling temperature in terms of the workability and formability of the material was 573 K. And the elongation and formability were maximal in sheets processed by 4–6 passes of DSR. Moreover, reversing the shear direction made the microstructure more homogeneous and finer than unidirectional shear, and improved the mechanical properties and formability. This improvement was greater in samples where the shear direction was reversed once in the middle than where it was reversed for each pass.

Abstract: The mechanical properties of the AZ31B alloy sheets processed by differential speed rolling (DSR) from the cast ingots homogenized at two different conditions were investigated. There still existed the uneven distribution of Al and Zn in the ingot homogenized at 673 K for 6 h, while it was homogeneous for the ingot homogenized at 723 K for 24 h. Compare with the sheet rolled from the ingot homogenized at 673 K for 6 h, the sheet rolled from the ingot homogenized at 723 K for 24 h exhibited a lower proof stress, a larger elongation, and a lager strain hardening exponent. The improvement in the ductility can be attributed to the elimination of the microsegregation of Al and Zn in the matrix.

Abstract: Cross-roll rolling with different rolling routes (unidirectional rolling and reverse rolling) was carried out on a commercial Mg alloy sheets. In the cross-roll rolling, the roll axis was tilted by 7.5 degrees against the transverse direction. As a result of the Erichsen tests at 433 – 493 K, the stretch formability of the reverse cross-rolled specimen was higher than that of the unidirectional cross-rolled specimen. The reverse cross-rolled specimen showed lower average Lankford value compared with the unidirectional cross-rolled specimen. This is likely to be responsible for the enhanced stretch formability of the reverse cross-rolled specimen. The higher stretch formability was attributed to reduction of (0002) texture intensity, which was originated from random grain distribution.

Abstract: Ti-Ca-P films on commercial pure (cp) titanium plates were uniformly deposited using dual target RF magnetron sputtering apparatus with DC magnetron sputtering system under the conditions of 50 W DC power to a cp titanium target and 200 W RF power to a β-tricalcium phosphate (β-TCP) target for 60 min in 2.2×10-1 Pa Ar. Resulting samples had smooth surface like mirror. Crystal structure of the film was amorphous. The film had the chemical composition of about 3: 1.7: 1: 11 in Ti: Ca: P: O ratio under controlling the β-TCP target RF sputtering power and the titanium target DC sputtering power. The film and the method are expected to be useful for remodeling surfaces of various titanium implants.

Abstract: Possibilities of the consolidation process using hot extrusion and subsequent hot rolling were investigated in order to recycle the cutting chips of the aluminum alloy efficiently. For the rolling process, differential speed rolling (DSR) was also applied in addition to normal rolling. Several kinds of cutting chips with different size and cleanliness were collected through turning 6061 aluminum alloy round bars. From these cutting chips, recycled material sheets were produced under various processing conditions via hot extrusion and subsequent hot rolling. Non-recycled material sheets were also prepared for comparison. All samples were characterized by optical microscopy, SEM(EBSP), X-ray texture analysis, tensile test and corrosion test. As a result, it was found that the recycled material sheets produced under optimum processing conditions had smaller grain sizes than those of the non-recycled ones, therefore the mechanical properties and the corrosion resistance of the recycled material sheets were almost comparable to those of the non-recycled ones. Moreover, concerning the DSR processed sheets, the traces of the chip interface, which were clearly observed in the normally rolled ones, almost disappeared, and the appearances were remarkably improved. Then the DSR processed sheets significantly surpassed the non-recycled ones in the tensile properties and the corrosion resistance.