Tomio Satoh

Superplastic-like behavior of rapid-solidification-processed hyper-eutectic Al-Si P/M alloys

Superplastic-like behavior of both P/M Al-25Si and Al-15Si alloys prepared from centrifugally atomized powders has been investigated. The maximum elongation of P/M Al-25Si and Al-15Si alloys are 154% and 307%, respectively. Although relatively high m value, larger than m = 0.4, is obtained at an early strain stage in tensile tests of the P/M alloys, the m value reduces to 0.33 or less with increasing strain. The testing temperature showing the maximum elongation of the P/M alloys is just below the each solidus temperature of the Al-Si alloys. The elongations of the P/M alloys extruded indirectly without pre-compaction of the powder by vacuum hot pressing, are larger than those of the alloys through vacuum hot pressing. A filament-like elongated microstructure, which may be caused by grain boundary sliding, is formed on the whole surface of P/M alloy under the optimum condition of the superplastic deformation. The shapes of primary silicon phase and cavity become more spheroidization under the condition of superplastic deformation. The fracture surface is also rounded at the optimum temperature exhibited the maximum elongation.

High-temperature deformation behavior of aluminum alloys produced from centrifugally-atomized powders

Abstract Powder metallurgy (P/M) aluminum alloys have been expected to have extended application in the production of such items as automobile, aeroplane and machine parts. P/M AlAl10mass%Mg and hyper-eutectic AlSi alloys have been produced using a centrifugal-atomization process, which is one of the rapid-solidification techniques, and the possibility of superplastic deformation has been investigated because the components required have become of more complicated shape. The ductility of the P/M alloys has been examined with respect to the effects of the test temperature, the strain rate and the consolidation process of the powders. P/M Al10Mg and AlSi alloys exhibit superplastic-like deformation behavior, and the optimum strain rate showing the maximum elongation is relatively high, 10 −1 −10 0 s −1 for the Al-10Mg alloy. The maximum elongations of the P/M Al25Si and Al15Si alloys are more than 150 and 300%, respectively. The P/M AlSi alloys show the maximum elongation at temperatures very close to the each solidus temperature of the alloys. A fibrously-elongated microstructure is formed on the whole surfaces of the P/M AlSi alloys under the optimum condition of superplastic deformation.

Joining of iron powder compacts by an infiltration method

Abstract Joining of iron powder compacts by an infiltration method was attempted. The joining strength of the compacts was investigated with respect to variations in roughness of the surface, applied pressure, relative density of preforms, infiltration temperature and the time. The joining strength was found to be almost equal to those of monobloc ompacts by conventional infiltration when the joining was done under the optimum conditions. Joining of the iron powder compact and wrought steel samples such as S10C and S55C was also carried out and high strength could be obtained by this method. Samples with complicated shapes or with holes in the parts could be easily made with the infiltration technique proposed.

Superplastic-like behavior of Al-high Si alloys produced from rapidly solidified powders and ribbons

The high temperature tensile properties of hyper-eutectic Al-Si alloys were studied at temperatures between 683 and 813 K at initial strain rates between 8.3X10−4 and 4.2X10−1s−1. The alloys were prepared from prealloyed powders and ribbons, which were respectively fabricated by the centrifugal atomization and melt spinning, through the hot extrusion process at an extrusion ratio of 110:1. The extruded alloy bars prepared from the powders and ribbons, i.e. the powder-extruded and ribbon-extruded bars, have homogenous micro-structures with the fine silicon particles dispersed in the aluminum matrices for the Al-25Si and Al-15Si alloys. The maximum elongation-to-failure of the powder-extruded bar and the ribbon-bar are almost equal, 150%, for the Al-25Si alloy, In the Al-15Si alloy, the ribbon-extruded bar has superior elongation compared to the powder-extruded bar, that is, these are respectively 520% and 400%. The maximum elongation was attained at the relatively high strain rate of 10−2s−1 independent of the silicon content and solidification process.

Improvement of Superplasticity of Zn-22Al Pre-alloy Powder by The Use of Rapid Solidification Technique and Heat-treatment Method

Zn-22Al pre-alloy powders were fabricated by air-atomized, argon-atomized and rapidly solidified methods. The rapidly solidified powder was fabricated by centrifugal atomization method. To improve the superplasticity of the air-atomized and argon-atomized powders, a simple heat-treatment of the powders, i.e, rapid cooling after heating at 380°C for half an hour, was attempted. Microstructures of the rapidly solidified and the heat-treated Zn-22Al pre-alloy powders were observed by optical microscope, SEM and TEM. It was found that the microstructures of the heat-treated powders were refined and granulated, and that also the grains became equiaxed in shape.Compactibility of the rapidly solidified powder was inferior to those made from the air-atomized and argon-atomized powders, because the shape of the rapidly solidified powder was nearly spherical. However, the refinement and homogenization of the rapidly solidified powder was almost same to those of the heat-treated powders and elongation of the compact reached about 1000%.