Papers by Author: Hajime Kato

Abstract: The influences of solution treatments, prior cold drawings and aging treatments on mechanical properties in Corson alloy with high contents more than 8.0 mass% of Ni and Si have been investigated. As a result of the optimization of conditions, the maximum hardness and tensile strength reached 306HV and 968MPa, respectively. Effects of temperatures of solution treatment and aging on the mechanical properties were analyzed based on solid solute concentrations in matrix phase, which were estimated by using the linear analysis and calculated from the electrical conductivity. The solute concentrations were also measured directly by SEM-EDS. Consequently, the precipitation hardening of the alloys was governed mainly by the solute concentrations of Ni and Si in matrix phase in solution treatment. The hardness depended on not only the solute concentrations but also the excess of Ni and Si in the alloys.

Abstract: Coarsening of grain structure in surface layers in 5454 and 5083 Al-Mg based alloy sheets has been made by continuous cyclic bending (CCB), which is a useful straining technique to produce the high strain on the surface layers and the lower strain in the central layer of the sheet, and subsequent annealing. The microstructure on cross-section of the samples was analyzed by SEM/EBSD technique. For the samples before and after CCB/Annealing corrosion behaviors in NaCl or HCl solution were investigated. As a result, the samples subjected to CCB/Annealing showed higher corrosion resistance on coarse-grained surface layers. Less change in the corrosive solutions was observed on the grains parallel to {001} or {111} plane.

Abstract: Superplasticity in an AZ80 magnesium alloy subjected to friction stir processing (FSP) has been investigated. FSP was carried out at two traveling speeds of 150mm/min and 300mm/min for grain refinement. Optical microscopy on cross section to processing direction revealed obvious differences in size and feature between the stir zones at the two traveling speeds. The hardness of FSPed sample at the room temperature was about 30HV higher than that of as-received one. The maximum stress of the FSPed sample was reduced remarkably at lower strain rates compared with those of the as-received one at 573K and 673K. On the other hand, the elongation to failure of the FSPed sample showed ten to thirteen times larger than that of the as-received one at 573K and low strain rates. Further surface morphology near the fracture tip was observed by scanning electron microscopy to discuss deformation mechanism at high temperatures.

Abstract: Microstructural characterization and temperature analysis have been performed in friction stir welding (FSW) of A383 and 5052 dissimilar aluminum alloys. Marked difference in microstructure was observed between joints with different arrangements of materials. The temperature at four points on each side of the joint line was measured during FSW in various conditions. In addition, an analytical model assumed that the work generated by the rotation of the tool led to the work for stirring materials and heat generation of the material and the tool. The temperature of the retreating side (RS) for the joint of the advancing side (AS):A383/RS:5052 was about 50K higher than that of AS, while the temperatures of AS and RS for the joint of AS:5052/RS:A383 were almost the same. The experimental temperature could be calculated reasonably by using the model with assumption of the work for stirring the material.

Abstract: Severe strain has been introduced to commercially purity (CP) titanium samples by means of friction roll processing (FRP), which represents an alternative severe plastic deformation technique by inducing shear strain. FRP has an excellent possibility of controlling surface microstructure combining with subsequent annealing. The resultant microstructure refinement and texture evolution has been investigated. Hardness of sample was measured to compare mechanical properties of samples before and after FRPed. Parameters including the different indentations given to the sample and sample feeding speed were experimentally conducted to find the optimum condition for investigating effect on microstructure evolution. After subsequent annealing, the evolutions of microstructure and texture were observed by field emission scanning electron microscopy (FESEM) and analyzed by scanning electron microscopy/ electron back scatter diffraction pattern (SEM/EBSP) technique. Transverse texture was found to be the preferred orientation existing in the thin top layer of the sample after FRP and annealed at 823K for 1h.

Abstract: The composite accompanied with a function of thermoelectric conversion has been fabricated. It was a fiber metal laminate (FML) consisting of two aluminum alloy sheets of 0.5mm thickness and a central layer of glass fiber reinforced plastic (GFRP). The central layer with a thickness of 1mm included thermoelectric elements of Bi-Te based alloys between glass fibers. The mechanical properties of FML with and without the thermoelectric elements were evaluated by tensile and bending test. The thermomechanical properties were measured by a potentiometer for a module with heated and cooled sides, and plotted a potential as a function of difference in temperature between both sides.

Abstract: Severely rolled sheets of Al-4.5%Mg-0.7%Mn based alloys have been prepared to achieve grain refinement leading to low temperature superplasticity. Rolling is one of straining technique which has a high possibility of industrial application. The alloys used were T1: base one adding 0.08%Zr and 0.05Ti for suppression of grain growth, F1: 0.80%Fe addition and F2: 1.92%Fe addition to increase nucleation sites of recrystallization. For comparison, M1: Al-4.2%Mg was also prepared. All of samples were 99.8% cold rolled to thin sheet 0.1mm thick. The maximum elongation of 150%, which was markedly large in consideration of specimen thickness of 0.1mm, was obtained at 533K and 1.4×10-3s-1 for T1 sample while the elongations for F1 and F2 showed less than 100%. On the other hand, M1 exhibited larger elongation of 190% at 533K and 1.4×10-3s-1. Further, difference in superplastic deformation of these alloys was investigated by using SEM/ EBSP analysis of intragranular misorientation, which reflects strain or stored energy generated during deformation with dislocation glide, to discuss the deformation mechanism.

Abstract: Grain refinement and high temperature deformation in two kinds of magnesium alloys subjected to friction stir processing (FSP) have been investigated. One was a rolled sheet of LA141Mg and another was a cast plate of AZ91Mg. FSP was developed by adapting the concepts of friction stir welding to obtain a fine grain size in a stirred zone. Grain refinement was achieved by FSP to give fine grain sizes of 11.4μm and 8.4μm for LA141 and AZ91 alloys, respectively. For LA141 alloy, the maximum stress of the FSPed sample was higher than that of the as-received one in the range of 300K to 523K while the elongation to failure of the former was considerably smaller than that of the latter. On the other hand, the elongation for the FSPed sample of AZ91Mg showed three times larger elongation with a lower maximum stress than the as-received cast one at 523K and 2.8×10-3s-1. Further difference in high temperature deformation for both magnesium alloys was discussed based on microstructural change and stress-strain curves.

Abstract: In-situ SEM/EBSP analysis has been performed during the evolution of the cube texture in a pure aluminum foil. In general, foils for capacitor are manufactured in an industrial process of casting, homogenizing, hot rolling, cold rolling (CR), partial annealing (PA), additional rolling (AR) and final annealing (FA). The foil samples after CR or AR in the process were analyzed by the SEM/EBSP technique at a constant temperature which was step-heated repeatedly by 10-20K from a room temperature to 623K or 598K. In a CRed sample, cube ({001}<100>) grains begin to grow preferentially at 503K to cover the sample. On the other hand, in a sample subjected to PA at 503K and AR, cube grains coarsened rapidly and preferentially at more than 533K in contrast to other oriented small grains remaining their sizes. Further, intragranular misorientation analysis revealed that the misorientation, which corresponds to dislocation density or strain, was much smaller in cube grains than in S ({123}<634>) and Cu ({112}<111>) ones.