The aim of this paper was to define the technology of casting of aluminum alloys and the process, to collect data of the melt preparation and to explain its influence on the mechanical properties and microstructure of the casting. The paper consists of theoretical and experimental part.The theoretical part explains the casting process of aluminium alloys with an emphasis on melting furnaces and melt treatment. A brief introduction to the casting process of the basic types of metal casting alloys is given. The role of aluminum and its alloys in foundry industry is described in detail. The classification of aluminium alloys is also given. The purpose of the melt treatment of aluminium alloys is explained as well as the influence of these treatment on the casting properties. In order to achieve the objectives of this paper, a laboratory study was performed in which the influence of melt treatment including grain refinement, modification and degassing on the microstructure and mechanical properties of AlSi12 aluminum alloy was investigated. For this purpose, samples of basic and treated AlSi12 alloy were cast. In order to obtain the results, a thermal analysis of the melt and an analysis of the chemical composition were performed. Also, tensile test and metallographic analysis of the test samples were carried out. Based on the results, it was shown that the melt treatment had positive effect on the microstructure and mechanical properties; the fine grain structure was obtained after melt treatment improving the tensile strength, ultimate strength and elongation.