A Study of Monotectic Al-Bi Alloys Rapidly Solidified from Melt

Abstract

This paper presents experimental results and theoretical considerations to investigate the effect of rapid cooling from melt on physical properties of Al-Bi alloys. A number of monotectic Al-rich binary alloys having limited solubility in the solid state have been pointed up as desirable for many industrial applications, e.g., self-lubricated bearings, electronic materials, superconductors and optical components. Monotectic alloys undergo an invariant reaction at the monotectic temperature, in which a liquid phase, L1, is decomposed into a solid phase, S1, and a liquid phase, L2. During cooling, the minority liquid phase forms discontinuous and isolate droplets or fibers within the Al-matrix. The competition between the growth of the minority phase and the rate of displacement of the solidification interface will determine if the prevalent morphology will be formed by droplets or fibers. Chill-block melt spinning technique was used to examine the possibility of casting Al-Bi monotectic alloys with possible homogeneous microstructure. The resulting microstructure was analysed by scanning electron microscopy and X-ray diffraction. The electrical resistivity, thermal parameters, internal friction, thermal diffusivity, elastic moduli and hardness of the melt-spun ribbons have been investigated as a function of composition. The results reveal that several combinations of strength, hardness, enthalpy, entropy change, resistivity and internal friction can be generated from the alloys to meet the needs of antifriction applications.