| Hypereutectic Al-16Si-5Fe based alloys fabricated by hot extruding air atomized powders were investigated for microstructure and tensile deformation behavior up to 520℃. TEM, SEM and EDS analyses revealed that very fine Al_5FeSi intermetallics and Si particles are uniformly distributed in the matrix which has the average grain size of 800nm. Elongation to failure increased with increasing temperature, with accompanying decrease in both yield and tensile strength at the initial strain rate of 1.4×10^(-3)s^(-1). Above 450℃, a high strain-rate superplasticity was observed, and the maximum elongation of 377% was achieved in the specimen deformed at 520℃ with the initial strain rate of 1.4×10^(-1)s^(-1). The superplastic deformation was considered to occur by a grain boundary sliding due to the extremely fine grains. Retarded grain growth during deformation owing to the uniformly distributed fine-precipitates was also considered to be an important factor for the superplasticity. A superplastically deformed specimen at 520℃ showed an evidence of a partial melting in the vicinity of grain boundary, suggesting that the liquid phase formed by the partial melting in the vicinity of grain boundary contributed as an accommodation helper, which relieved the stress concentration arised from the grain boundary sliding. |
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