Microstructural characterization and artificial aging of compo-casted hybrid A356/SiCp/Grp composites with graphite macroparticles

Hybrid A356/SiCp/Grp composites were produced via compo-casting using the A356 aluminum alloy as the composite matrix, with silicon carbide microparticles (SiCp) and graphite macroparticles (Grp) as reinforcements. The effect of the thixocasting process on the microstructure of a modified A356 alloy (with 0.03 mass% of strontium) was considered. The microstructures of the thixocast A356 alloy and the synthesized composite materials were examined by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD). The fracture surfaces of the composite matrix and the composites were also analyzed. The thixocast A356 alloy and the composites were subjected to artificial aging after a solution heat treatment. Aging kinetics was followed by hardness measurements. Differential scanning calorimetry (DSC) was applied to reveal the presence of phases formed during artificial aging. The composites reached maximum hardness faster than the thixocast A356 alloy. The time required to attain peak hardness decreases with the increase in the content of particulate reinforcements.