Microstructural Explanation of the Mechanical Properties of Al – GNPs Composites with Al4C3 Produced by Powder Metallurgy Method and Extrusion

The microstructure of aluminum-based composites with graphene reinforcement in the range of 0.1 to 1.1 wt. %, obtained by powder metallurgy and extrusion, has been characterized. The first series of composites was produced by extrusion at a temperature of 500 °C, at which in situ aluminum nanoscale carbides were formed, and the second by extrusion at 400 °C and subsequent annealing at 610 °C for three hours, at which nano- and microscale carbides were formed. The methods used for investigation are mechanical testing, optical microscopy, SEM and TEM. The mechanical properties and failure mechanisms of composites with in situ obtained aluminum carbides and with carbides obtained after annealing have been explained by means of the microstructural features. The first series of composites has higher strength and plastic properties than the second series. The better complex of mechanical properties of the first composites is due to the in situ formation of nano-sized carbides with a rounded shape, which limits the manifestation of carbide embrittlement and, accordingly, the deterioration of the mechanical properties of the composites. In addition, the rounded nano-carbides form dimples in the fracture surface of the composites, which is a prerequisite for favoring the plastic properties.