Microstructure characterization and evaluation of mechanical properties of stir rheocast AA2024/TiB 2 composite

Abstract

In this research, microstructure and mechanical properties of stir rheocast AA2024/TiB₂ metal matrix composite have been investigated. The working temperature was 640℃, which was the selected semisolid temperature that corresponds to 40% of the solid fraction. Two weight percentage, 4 wt%, and 6 wt% of the TiB₂ reinforcements were added to the matrix. The field emission scanning electron microscope micrographs of the developed composites showed a uniform distribution of the particles in the case of the 2 wt% and 4 wt% of the reinforcements. However, the particles agglomerated as the weight percentages of the reinforcement increases to 6%. The optical microscope of the liquid cast sample showed the dendritic structure, whereas the rheocast samples showed a globular structure. The X-ray diffraction analysis confirmed the distribution of the reinforcements in the matrix and the formation of some intermetallic compounds. Mechanical properties significantly improved by the addition of the reinforcements in the matrix. An increase in tensile strength of 13.3%, 40%, 28%, and 5% was achieved for the unreinforced rheocast sample, 2 wt%, 4 wt%, and 6 wt% reinforced rheocast samples respectively, compared to the liquid cast sample. An increase in 20% of hardness was attained for the composite with 2 wt% TiB₂ compared to the liquid cast sample. According to the fractography analysis, small dimples were observed on the fractured surface of the unreinforced rheocast sample, whereas small and large voids were dominant on the fractured surface of the 2 wt% composite, which shows the ductile fracture mode.