EFFECT OF TRANSITION METALS ON AS-CAST ALUMINUM ALLOYS MICROSTRUCTURE COMPOSITION

10.25712/ASTU.1811-1416.2022.04.011

Abstract

The study addresses the effect of aluminum alloys complex alloying with magnesium, manganese, scandium, zirconium and hafnium. For this purpose, A85 ingots as well as Al–Mg, Al–Mg–Sc, Al–Mg–Mn–Sc system alloys and 1570 alloy, including those with 0.5 % hafnium additions were cast into a steel mold. Microhardness, electrical conductivity, grain structure, intermetallic inclusions and mechanical properties were studied for all alloys. For 1570 and 1570 + 0.5 % Hf alloys, Al₃(TE1x, TE2(1-x)) type nanoparticles were additionally studied using transmission electron microscope. Grain structure analysis showed that magnesium, and then manganese content increase, as well as scandium addition (up to 0.4 %) gradually reduce the grain size. However, overall grain structure maintains its dendritic structure. An equiaxed structure appears only with combined addition of scandium-zirconium, while hafnium addition facilitates its extra refinement. Increasing alloying elements content leads to the growing number of large intermetallic particles, forming during crystallization. It should be noted that many coarse non-equilibrium particles contain large amounts of scandium and zirconium. Hafnium additions reduce scandium and zirconium amount in coarse intermetallic particles, increasing their content in supersaturated solid solution. The increasing content of fine particles, formed during ingot cooling, is observed as a result of discontinuous decomposition only after combined addition of scandium-zirconium. With hafnium addition precipitation of nanoparticles from a supersaturated solid solution practically stops during ingot cooling. As-cast mechanical properties grow initially due to solid-solution hardening and grain refinement, and then due to particles Al₃(Sc,Zr) type particles emergence.