Improving the properties of copper alloys by melt refining and modifying treatment with alkaline-earth metal carbonates

The paper analyzes main tasks related to brass melt processing. It provides a comparison of traditional processing methods with the proposed method of alloy quality improvement. The equilibrium conditions for carbonate decomposition reactions are considered when processing the melt in an open and closed ladle. Conditions for the carbonate decomposition reaction are formulated. The study proves that the resulting gaseous product of carbonate decomposition can have a simultaneous flotation effect on the brass melt refining from dissolved gases and non-metallic inclusions. The paper analyzes thermodynamic conditions of slagging impurities by introducing alkali and alkaline earth metal carbonates through the interaction of their oxides with silicon and aluminum oxides in the melt. The study considers the possibility of enhancing the physical and mechanical properties of brass castings due to the modifying effect provided by the formation of calcium, strontium, barium and sodium oxides resulting from dissociation of their carbonates. The paper describes the technology used for brass melt processing with alkaline earth metal carbonates in a pouring ladle, methods for studying the obtained results from the point of view of microstructural analysis and mechanical test values. It is found that the use of carbonates in brass melt processing creates a more favorable microstructure, contributes to the lower average nominal grain size, increases its uniformity, and reduces the likelihood of enlarged α phase formation. Structural parameters of samples were extensively studied with various options of melt processing with carbonates. Mechanical properties of brass samples were studied before and after melt processing with various combinations of alkaline earth metal carbonates. Compositions of carbonate mixtures that have the most favorable integrated effect on the brass strength with a simultaneous increase in plasticity performance were determined. The optimum carbonate mixture composition was chosen experimentally. Processing efficiency was confirmed by industrial tests. The simplicity and other positive features of the proposed technology for refining and modifying brass melt processing with mixtures of alkaline-earth metal carbonates were observed.

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