Three types of aluminum alloys such as AlSi7Mg, AlSi12Cu2MgNi and AlZn4 are refined by introducing nanoparticles of high melting temperature compounds—nitrides and carbides as well as diamonds in the melt. Their influence on microstructure, mechanical and some electrochemical properties of castings of these alloys is investigated. It is established that the microstructure is refined, the porosity is decreased, and some mechanical and electrochemical properties such as protection potential in drinking water are increased. The mechanism of grain refinement and silicon modification is discussed.

Reinforcement of aluminum and aluminum alloys with graphene has been intensively practiced by researchers in the past dozen years. The role of Al₄C₃, which could be produced unintentionally or purposefully during the composite production, was controversial until it was found that nano-sized carbides were beneficial for strengthening the composites. aluminum-graphene-nano-sized Al₄C₃ composites were produced by us using the powder metallurgical method and subsequent annealing. The microstructure was investigated using light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution transmission electron microscopy HRTEM. Nano-sized carbides were found at the interface aluminum-graphene. The formation of a chemical bond between aluminum and graphene during annealing was proved. Lower values of the microhardness and strength characteristics of the composites after extrusion and subsequent annealing during which nano-sized carbides are formed were found in comparison with those obtained after extrusion. It could be supposed that the annealing processes contribute more to the reduction in microhardness and strength characteristics than nano-sized carbides contribute to its increase. The presence of a strong chemical bond between the graphene and the aluminum is manifested in the failure pattern, which is characterized by graphene nano-platelets and nano-sized carbides fracture and semi-pulled out or semi-slipped Al₄C₃ from the matrix.