Microstructure and Mechanical Properties of Rapidly Solidified Al-16Si-5Fe Based Alloys

초록

Microstructure, hardness and tensile properties up to 793K were investigated by using Al-16Si-5Fe based alloys fabricated by a powder metallurgy(PM) route though the hot extrusion of rapidly solidified powders. Also, microstructure was compared with an ingot metallurgy(IM) processed material having the same composition as the PM alloy. The PM alloy showed very fine Al5FeSi intermetallics and fine Si particles which were uniformly distributed in the matrix having the average grain size of 800㎚, whereas the IM alloy exhibited a coarse microstructure. Hardness of the PM alloy did not decrease markedly after holding up to 673K for 2h. Elongation to failure of the PM alloy increased with increasing temperature, with accompanying decrease in both yield and tensile strength at the initial strain rate of 1.4×10-3s-1. Above 723K, a high strain-rate superplasticity was observed, and the maximum elongation of 380% was achieved in the specimen deformed at 793K with the initial strain rate of 1.4×10-1s-1. The superplastic deformation was considered to occur by a grain boundary sliding due to the existence of extremely fine grains. Superplastically deformed specimens showed a limited grain growth owing to the presence of thermally stable fine-scale Al5FeSi intermetallics. Also, the existence of a filament-like phase in the superplastically deformed specimens suggested the formation of a liquid phase which can accomodate the stress concentration arising from grain boundary sliding.