Aluminum matrix composites are important applicable materials for automotive and aerospace industries. Lightweight, environmental resistance, high specific strength and stiffness, good wear resistance and high thermal and electrical conductivity are characteristics that promote research and development to extend their applications by further improvement in the properties. Ceramic particles are the most widely used materials for reinforcement of aluminum alloys. Boron carbide (B 4 C) is one of the most promising ceramic materials due to its attractive properties, including high strength, high melting point (2450 ° C), low density (2.52 g/cm 3 ), extremely high hardness (the third hardest material after diamond and boron nitride), good chemical stability and neutron absorption capability. The combination of these properties makes it an interesting candidate for neutron absorption materials, wear resistant materials, electrode materials and cutting tools. In addition to many uses of sintered shapes, particulate B 4 C has been used as reinforcement for metal and ceramic matrix composites for increasing wear resistance. More recently, Considerable attention has been paid to Al-B 4 C composites. In this study, aluminum matrix nanocomposite reinforced by boron carbide nanoparticles was produced using mechanical milling and hot pressing methods. For fabrication of this nanocomposite two general paths were considered. First path involved insitu formation of B 4 C nanoparticles in Al matrix by ball milling of Al-B-C powder mixtures. The second path included two ste preparation of B 4 C nanoparticles by mechanochemical route and then ball milling of B 4 C with pure Al powder to obtain Al–B 4 C nanocomposite. In order to produce of B 4 C nanoparticles, various routs such as milling of elemental B-C mixture, carbothermic reduction of boron oxide (B 2 O 3 ), aluminuthermic and magnesiothermic reduction of B 2 O 3 in the presence of carbon were investigated. Morphological and structural changes of powders during mechanical milling were examined using scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) analysis. Results showed that ball milling of Al-B-C powder mixture did not yield B 4 C in Al matrix even after long milling time. Subsequent heat treatment of this mixture led to the formation of undesirable phases. In mechanochemical route only magnesiothermic reduction of B 2 O 3 in the presence of carbon led to the formation of B 4 C phase. XRD analysis and transmission electron microscopy (TEM) observations confirmed that magnesiothermally synthesized B 4 C had nanometer size ranging from 10 to 80 nm. The prepared B 4 C nanoparticles wer
