Effect of Adding Rare-Earth and Alkaline-Earth Metals to Aluminum-Based Master Alloys on the Structure and Properties of Hypoeutectic Silumines

The paper presents the results of comparative studies on the modifying ability of La, Sc (REM group), and Sr (AEM group) in the processing of a GK-AlSi10Mgwa alloy (Al–Si–Mg system). The elements were introduced into the melt in the form of AlLa12, AlSc2, and AlSr10 master alloys in the same amount (0.25 wt.%). The effects of the added elements on the microstructure, mechanical properties, and electrical conductivity in the cast state were evaluated. Structural homogeneity was evaluated along the height of the plate samples according to recorded electrical conductivity values. Varying degrees of modification were used to enhance the mechanical properties and electrical conductivity of the GK-AlSi10Mgwa alloy. While, upon modification with Sr additives, the maximum increase in ultimate strength (by 60–66%) was noted, the HB hardness and the relative elongation of the alloy increased to a lesser extent in comparison with modification by La and Sc. Modifiers of the REM group (La and Sc) altered the morphology of the main phases in different ways. In La-modified samples, the morphology of eutectic silicon crystals was changed from lamellar to fibrous. Modification by Sc additives caused similar changes in the morphology of eutectic silicon with partial modification of α -Al dendrites. In terms of modifying α-Al dendrites and eutectic silicon crystals, strontium – an alkaline-earth metal – had the greatest effect. Such modification leads to changes in the alloy structure, eventually resulting in increased electrical conductivity. Although the maximum increase in electrical conductivity was brought about by Sr-modification of the alloy samples, the fact that this change is not significant indicates an increase in the homogeneity of the microstructure.