| Microstructures of rapidly quenched Al-Co alloys made by a melt spinner were investigated and in-situ decomposition behavior of the solidified microstructures were also studied. Two regions of microstructures were observed in the as-quenched strips; one was a chilled structure formed on the side facing the copper substrate and the other was a free surface structure on the opposite side The chill structure consisted of micrograins and fine precipitates, i.e. B phase, which are metastable and have (001)_(At),//[001]_B and (130)_(At)//[110]_B orientation relationship with Al matrix. The free surface structure was composed of large and stable Al_9Co₂ precipitates surrounded by microdendritic, eutectic and cell structures. Upon annealing it was found that the finer the micro-structure, the faster the decomposition accompanied by nucleation of the slowly growing precipitates. The microhardness of the as-quenched structure increased with increasing Co contents and with addition of the third elements, and the value decreased monotonically with aging time and temperature. Among the various third elements tried, Mn showed the most effective results in hardness increase. |
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