Shigehiro Kawamori

Mechanical Properties of Hot-Pressed Compacts Made by Alumina Particle Dispersion Magnesium Powders

To enhance the mechanical properties of Mg alloys, powders of pure Mg (Al2O3/Mg) dispersed with over 10 vol% Al2O3 particles were formed by ball milling powder mixtures of pure Mg and Al2O3 particles with particle sizes of 0.3 and 1 μm. The effect of the Al2O3 content of hot-pressed discs of Al2O3/Mg powders on the mechanical properties was investigated. The hardness increased sharply at certain Al2O3 content. This is considered to be because of the development of Al2O3 particle strengthening due to the excellent interfacial bonding between Mg and Al2O3 particles when the Al2O3/Mg discs contain a sufficient amount of Al2O3 particles and have a sufficient interparticle distance. The maximum hardness was 220 HV. The tensile strength increased as Al2O3 content was increased. The Al2O3/Mg plate with Al2O3 particles sizes of 0.3 and 1 μm indicated maximum values of the bending strength at 10 and 14vol%Al2O3 content, respectively.

Effects of Sintering Conditions on the Mechanical Properties of Alumina Particle Dispersed Magnesium SPS Compacts

To enhance the mechanical properties of Mg alloys, 0-30vol% Al2O3/Mg powders were formed by ball milling powder mixtures of pure Mg and Al2O3 particles, and then Spark plasma sintering (SPS) compacts (Al2O3/Mg discs) were made by the Al2O3/Mg powders. The effect of the cooling conditions in the SPS process on the mechanical properties of the Al2O3/Mg discs was investigated. From the results of SEM, XRD and TEM-EDS, the microstructures of the Al2O3/Mg discs were identified to consist of α-Mg solid solution, Al2O3 particles, refined MgO particles and refined needle-like Mg17Al12 ( more than 20vol% Al2O3 content). The mechanical properties of the discs were able to control by the regulation of the cooling conditions (cooling rate (vc) and applied pressure in the cooling (pc)) in SPS process, and as a result, the SPS discs possessing the mechanical properties beyond HP compacts were obtained under the cooling conditions of “vc= 0.83K/sand pc = 20MPa”. Main factor that the cooling conditions in SPS process effect on the mechanical properties of the Al2O3/Mg discs are considered to be the compresive residual stress generated in the α - Mg solid solution by the thermal stress associated with deference of the coefficients of thermal expansion between the α - Mg and ceramics particles (Al2O3 and MgO) in the discs.

Fabrication Of Double Wall Tube By U‐O Press Forming And Pulsed Gas Tungsten Arc‐welding

Double walled tubes were trially fabricated by press‐forming and arc‐welding, as difficulty in fabrication was anticipated in the case of roll‐forming. U‐O press‐formed double walled sheets are TIG arc‐ welded. For determination of welding conditions, overlapped flat sheets were employed and butt‐welded including pulsed arc‐welding. Pulse from 1 to 100Hz is effective to obtain penetrated weld bead. With this, the double walled tube could be arc‐welded, which could not be achieved by conventional TIG arc‐welding.

Joining of Polycarbonate Ring/Disk to Metal Sheet/Shaft and its Easy Disassembly

For the possibility of easy disassembly of a joint assisted by strain recovery, the joint is fabricated with a cold rolled circular polycarbonate (PC) disk embedded in the center of an aluminium or a PC disk. Also, a shaft and a hollow circular disk are assembled by compressing or press fitting a cold rolled PC ring into the gap between them. First, the cold rolled polycarbonate disk is heat treated and the change in geometry is examined. Secondly, in order to evaluate joint strength, shear force and torque of the assembled joints are discussed with regard to reduction in thickness, tool clearance and interference. Lastly, joints are heat treated and the disassembly is checked. The cold rolled disk is recovered with the temperature 190°C for 20min. In embedding, disk compression in addition to rolling reduction is effective in increasing joint strength. In fabricating the shaft/disk joint, deformation of polycarbonate was not effective due to the recovery in room temperature after joining, while press fitting of the polycarbonate ring could fabricate the assembly. Heat treatment helped the joint to be automatically disassembled. The directly joined parts became completely apart, but the shaft/disk joint was disassembled only between the ring and the disk.