Koichi Makii

A two-step processing route for achieving a superplastic forming capability in dilute magnesium alloys

Superplastic ductilities were achieved in a dilute magnesium alloy containing 0.6% Zr through the use of a two-step processing procedure in which the basal planes are initially aligned through extrusion and the grain size is then refined using equal-channel angular pressing. The results show a maximum tensile elongation of >400% at 573 K when using an initial strain rate of 3.3×10?4 s?1.

In situ observations of compressive behaviour of aluminium foams by local tomography using high-resolution X-rays

We have investigated the compressive behaviour of closed-cell aluminium foams using a high-resolution X-ray CT. The microstructures of cell walls or Plateau borders in the foams were visualized in 3D using the local tomography technique which is a high-resolution CT method to reconstruct a region of interest within a large sample. The shapes and the 3D distribution of micropores, particles, and regions of solute segregation in the foams are evaluated, comparing the cell walls with the Plateau borders. Under compressive loads, the damage behaviour of such microstructures has been observed using an in situ test rig. It is found that the microcracks were mainly initiated from the cell walls and the micropores with large diameters were also damaged. The crack initiation sites are classified from the results. In addition, a method for non-destructive characterization of elastic and plastic deformation in the foams, which is called a 3D microstructure gauge (MG) method, is presented. Thousands of micropores as markers on each load were automatically matched by the information of those volumes and surface areas. The local strain mapping by the MG indicates that the edges of the micropores with large diameters have large strain under compression and this is consistent with the crack analyses.

Influence of Si on nano sub-structure of cementite lamellae in pearlitic steel wires

Abstract Microstructures of hot dip galvanized pearlitic steel wires were investigated by TEM to understand the influence of Si on sub-structure of cementite lamellae in pearlitic steel wires. The following conclusions were obtained: 1. 1) Each single crystal cementite lamella turned into aggregation of nano sub-structure after cold drawing and blueing over 673K. 2. 2) The diameter of the nano sub-cementite is controlled by blueing temperature and Si content.

Capability of superplastic forming in the seismic device using Zn–22Al eutectoid alloy

Abstract For the purpose of the improvement and mass-producing of a superplastic damping device, the mechanical properties in the extruded samples and the capability of superplastic forming were investigated. The mechanical properties after superplastic forging satisfied the performance needed to utilize in practice.

In Situ Observation of Fracture of Aluminium Foam Using Synchrotron X-Ray Microtomography

Synchrotron X-ray microtomography has been utilized for the 3D characterisation of microstructure in the cell materials of aluminium foams. Tomographs, consisting of about 109 isotropic voxels with a maximum of 1.0µm edge, were collected at the SPring-8 in Japan. A combination of high-resolution phase contrast imaging technique and several state-of–the-art application techniques has enabled the quantitative image analyses of micro-pore, intermetallic particles and grain boundary as well as the assessment of their effects on compressive deformation and fracture behaviours in two kinds of aluminium foams.

Application of Local Tomography Technique to High-Resolution Synchrotron X-Ray Imaging

X-ray CT method is a kind of nondestructive inspection, but has strong limitation in sample size due to a small field of view (FOV). The higher the resolution, the smaller FOV is, mainly due to the element number of available detectors commercially. Therefore, sample machining is more or less necessary so that the sample size is fit within the small FOV in the case of the high-resolution observation. Local tomography technique enables a high resolution reconstruction of small region of interests within a sample without the sample machining. In this study, we have evaluated the size effects of aluminum foam samples in terms of the 3D image quality by the local tomography techniques.

Application to Seismic Dampers in High-Strain-Rate Superplastic Zn-Al Alloy

High strain rate superplasticity has been realised at room temperature for the first time with a ultra fine grained Zn-22wt%Al alloy. Zn-Al alloys have some advantages over low-yieldpoint steels in their low work-hardening rate and high ductility. In addition, Zn-Al alloys are environment-conscious because of no harmful metal like Pb. However, when Zn-Al alloys are subjected to plastic deformation, the strain is localised and local fracture can take place because of their low work-hardening property. In this study, a seismic damper was designed with a Ultra fine grained Zn-Al alloy. As a result, an ecological and high performance seismic damper, the so-called “maintenance-free seismic damper”, has been successfully developed.

Application of High-Strain-Rate Superplastic Zn-Al Alloy to Seismic Dampers and its Optimised Shape Design

As a new damping material, the authors first developed a Zn-22wt.%-Al eutectoid alloy with ultra-fine grains exhibiting superplasticity at room temperature by means of thermomechanical controlling processes (TMCPs). The Zn-Al alloy has a few advantages such as low work-hardening rate and high ductility over a conventional seismic damping material, for instance, a low-yield-point steel. In addition, Zn-Al alloys are environment-conscious because of no harmful metal like Pb. However, when Zn-Al alloys are subjected to plastic deformation, since its work hardening is small, plastic deformation proceeds locally so that required absorption energy cannot be sufficiently obtained, and local fracture and local deformation instability can take place easily, which is the intrinsic characteristic of superplastic materials. Therefore we attempted to develop a shear panel type, a brace type damper for tall buildings and a bending type damper for Japanese wooden houses using FEM analysis in order to minimize localized strain and local deformation and to determine the optimum shape for this Zn-Al superplastic seismic damper. As a result, an ecological and high-energy absorption seismic dampers, so-called “maintenance-free seismic damper,” was successfully developed.

Three-Dimensional Zinc Mapping inside Aluminum Foams Using Synchrotron X-Ray Microtomography

Three-dimensional zinc mapping based on X-ray K-edge scanning has been performed. By microtomographies with energies above and below the K-absorption edges of the elements, the concentration distribution of the elements is evaluated during in-situ experiments, respectively. It is found that the Zn concentration distribution during the heat treatment was changed inside the cell wall of the aluminum foams and it has been homogenized. Also several precipitated phase transformation can be three-dimensionally visualized by the CT-method tuning X-ray energies.

Post-Mechanical Properties of Superplastically-Forged Zn-22wt%Al Alloy

Recently, the superplastic damping device, which has been using Zn-22wt%Al alloys with an ultra-fine grain size, has been put into practical use for a high-rise building. For the purpose of the improvement and mass-production of a superplastic damping device, the investigation about the superplastic forming and the characterization after the forging was carried out. As the results of FVM analysis, it was verified that the high effective stress and strain occurred at the corner and in the interior of the formed samples, respectively. However, the microstructure and mechanical properties after the forging were almost equivalent to those before the forging.