Effect of heat treament on microstructure and mechanical properties of squeeze cast AA6061 aluminum alloy

摘要

A series of cylindrical shaped monolithic AA6061aluminum alloy ingots, having 50 mm diameter and 85 mm length,were cast either by gravity die casting or squeeze casting under100MPa pressure. Also, AA6061/Al_2O_3 composite wasmanufactured by melt infiltration under 100MPa using Al_2O_3short-fiber preform. The resulting microstructures and mechanicalproperties of these castings were examined in the as-cast and heat-treated conditions. The specimens were solution heat treated at540degC for 1hr, quenched in cold water, and finally aged in saltbath at 180degC for various hours. Squeeze casting producedsound casting of refined microstructure and also decreasedmicrosegregation in the interdendritic regions due to rapid heatextration and increase in solubility of the solutes. Melt infiltrationof AA6061 aluminum alloy into Al_2O_3 short-fiber preformwas successful under 100Pma, and the matrix produced even finermicrostructure, compared to monolithic squeeze cast AA6061.Maximun microvickers hardness and tensile strength values werehigh in the order of melt infiltrated composite, squeeze castmonolithic and gravity die cast monolithic in the as-cast condition.Also, subsequent heat treatment improved hardness and tensilestrength and the maximum values were reached with shorter ageingtime in the same order.