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