Comparative studies on the microstructure and mechanical properties of bimodal and trimodal Al2024 based composites

The bimodal and trimodal aluminum based composites were produced by mechanical milling and hot extrusion. To produce trimodal and bimodal composites, primary powders were first milled using the attrition mill under argon atmosphere up to 50h and then were combined with coarse grained aluminum in 30 and 50wt%. The milled powders were formed by hot pressing and then were exposed to hot extrusion at 570°C with extrusion ratio of 10:1. Microstructure of hot extruded samples was investigated by optical microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with EDS spectroscopy. The mechanical properties of samples were also compared using tensile, compression and hardness tests. The results show that, after 50h milling and addition of 5wt% B4C, the strength of Al2024 alloy increases from 340MPa to 582MPa and its hardness increases from 87HBN to 173HBN but the elongation decreases from 14% to 0.5%. By adding the coarse-grained aluminum powder, the strength and hardness decrease slightly but the ductility increases in return. Furthermore, the strength and hardness of trimodal composites were higher but their ductility was lower.