EFFECT OF ZIRCONIUM ON THE MICROSTRUCTURE OF CAST ALUMINUM ALLOYS

Abstract

A comprehensive study was carried out to investigate the effect of zirconium strengthening additions on the formation of microstructure and phase composition of cast aluminum alloys of the Al−Cu−Mn (AlCu5) and Al−Si−Cu (Si8Cu3) systems. The importance of this research lies in the development of new lightweight structural materials with enhanced mechanical characteristics.The introduction of zirconium into the melt in the form of zirconium tetrafluoride (ZrF₄) in amounts from 0.6% мас. to 1.8% мас. at a temperature of 750 °C, as part of a flux composition, prevents contamination of the aluminum melt with iron. SEM observations together with local X-ray spectral analysis demonstrated that zirconium initiates the transition from a dendritic to an equiaxed fine-grained structure of the α-Al solid solution.The introduction of zirconium from its tetrafluoride in the above-mentioned amount promotes effective grain refinement of the α-Al solid solution through a heterogeneous nucleation mechanism on primary crystals of the Al₃Zr phase and complex compounds Zr(Al_1-x,Si_x)₃, which exhibit high crystallographic compatibility and a coherent bond with the matrix. Local X-ray spectral analysis revealed the distribution of alloying elements among structural constituents. Analysis indicates that the optimal zirconium content (0.6% мас.) ensures a uniform fine-grained morphology and offers potential for further dispersion strengthening by nanoscale structural components.In contrast, increasing the modifier content to 1.8% мас. leads to the formation of excessive massive intermetallics with needle-like and cross-shaped morphology (Zr content up to 65.54% мас.), which may negatively affect ductility. In the Si8Cu3 alloy, Zr transforms iron-containing phases, converting needle-like inclusions into plate-like forms. These findings can guide the design of technological processes for producing high-strength castings for critical applications.