Microstructure and stress-strain responses of Al-Mg-Si alloy matrix composites reinforced with 10 vol.% Al₂O₃ particulates

In this study, the microstructures and mechanical properties of underaged and peak-aged 6061 Al-Al₂O₃ particulate composites were investigated. In the underaged composites, small spherical zones were observed and, in the peak-aged composites, needle-shaped Mg₂Si precipitates were observed throughout the matrix. The stress-strain responses of the 6061 Al matrix composites were observed to be similar to those of commercially pure Al matrix composites reinforced with 10 vol.% Al₂O₃ although 6061 Al matrix composites were found to be stronger. Unlike 7xxx Al matrix composites in which the flow stress fell off at high strain rates, the flow stress of 6061 Al matrix composites increased rapidly at high strain rates. The work hardenability of the underaged composites was found to be greater than that of the peak-aged composites. Dislocations were observed to be distributed rather homogeneously irrespective of the matrix microstructure. Some Al₂O₃ particulates were observed to crack when the flow stress exceeded the critical flow stress, namely 415 MPa. Pores frequently observed near cracks in Al₂O₃ of the composites suggest that cracks may initiate and grow easily in the presence of pores.