Treatment of Al-7%SiMg Silumin with an Exothermic Mixture Containing NaNO3 and NaClO3

Abstract. Hypoeutectic silumins are one of the most popular groups of casting alloys. A problem with the use of hypoeutectic silumins is their microstructure, which negatively impacts their performance. The primary negative impact is exerted by the unmodified eutectic β phase, which constitutes natural microstructural notches. Methods for refining the microstructure of these alloys, thereby enhancing their properties, have been known in industrial practice for many years. One method is the treatment with exothermic mixtures. This method allows not only for modifying the microstructure but also for introducing chemical elements and compounds into the alloy that influence the properties of the silumins. Therefore, the research topic in this area remains partially unexplored. This confirms the need for further research on this modification method. The paper presents the treatment of hypoeutectic silumin containing 7% Si and the addition of magnesium using sodium nitrate (NaNO3). This compound was added to the alloy, which was then combined with aluminum and magnesium. The resulting mixtures produced an exothermic effect. A NaClO3 compound was also added to the alloy, which was expected to strengthen the alloy. The experimental results indicate that sodium nitrate affects the refinement of the eutectic β phase and improves mechanical properties. The addition of the NaClO3 compound increased the alloy's tensile strength and hardness while reducing its ductility.