Kunio Okimoto

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.