| A study has been made on the effects of additional elements on solidification structure, decomposition of supersaturated solid solution, and changes of microhardness in Al-Cr and Al-Cr-(Fe, Co, Ni) alloys made in flake form by the atomization-splat quenching method. Also, the variations in vickers hardness and high temperature tensile strength have been investigated in order to estimate the mechanical properties of the extruded bars. In Al-Cr-(Fe, Co, Ni) alloys, the progress of solidification was affected not only by the heat flow, but also by the intermetallic compounds acting as nucleation sites. As a result, a more homogeneous solidification structure was obtained. The crystallographic structure of intermetallic compounds in Al-Cr-Fe alloy was observed to have icosahedral symmetry. In the case of isochronal aging (1 hr) of splats, maximum microhardness was observed at 420℃ in Al-Cr-Fe, Al-Cr-Ni alloys, and at 400℃ in Al-Cr-Co alloy. The isothermal aging showed no changes of microhardness at 300℃, but a decrease was observed after 10 hr at 400℃ The isothermal aging of the extruded bars showed that Al-Cr-(Fe, Co, Ni) alloys had good thermal stability up to 350℃ and Al-Cr-Fe alloys had the most excellent tensive strength at the high temperature. |
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