| A series of cylindrical shaped monolithic AA6061 aluminum alloy ingots, haying 50 ㎜ diameter and 85 ㎜ length, were cast either by gravity die casting or squeeze casting under 100 ㎫ pressure. Also, AA6061/Al₂O₃composite was manufactured by melt infiltration under 100 MPa using Al₂O₃ short-fiber preform. The resulting microstructures and mechanical properties of these castings were examined in the as-cast and heat-treated conditions. The specimens were solution heat treated at 540℃ for 1hr, quenched in cold water, and finally aged in salt bath at 180℃ fur various hours. Squeeze casting produced sound casting of refined microstructure and also decreased microsegregation in the interdendritic regions due to rapid heat extration and increase in solubility of the solutes. Melt infiltration of AA6061 aluminum alloy into Al₂O₃ short-fiber preforms was successful under 100 MPa, and the matrix produced even finer microstructure, compared to monolithic squeeze cast AA6061. Maximun microvickers hardness and tensile strength values were high in the order of melt infiltrated composite, squeeze cast monolithic and gravity die cast monolithic in the as-cast condition. Also, subsequent heat treatment improved hardness and tensile strength and the maximum values were reached with shorter ageing time in the same order. |
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