Study of the Influence of Modification by Nanocompositions both on the Process of Crystallization and on the Structure of Aluminum Alloy AlSi7Mg

A study of the cast alloy A356, modified by various types of nanoparticles has been carried out. SiC, AlN, TiN, clad by Cu, Ag and Al have been used. The cladding has been done by the following methods: currentless chemical method, extrusion of a composite rod, tableting and mechanical-chemical treatment in a planetary mill. The obtained nanocompositions (NCs) have been introduced into the crucible of the furnace. Homogenization has been conducted after that by using an impeller. The samples have been cast in thin-walled steel containers. The non-stationary temperature has been measured during cooling and crystallization. Data about the dependencies of the temperature on time have been obtained and the magnitude of overcooling for the cases with and without NCs has been determined. It has been established for the samples with NCs, decreasing of the overcooling and grain refinement, with an average diameter of the α-grains decreasing from 21% to 60%. For the sample, modified by NC, SDAS (Secondary Dendrite Arms Spacing) decreases by about 14%, while the micro-hardness increases by 7.7%, compared to the unmodified sample. These studies reveal new information about the influence of the NCs on the process of crystallization of А356 alloy.