Study on the Formation and Precipitation Mechanism of Mn₅Si₃ Phase in the MBA-2 Brass Alloy

Mn₅Si₃ is an attractive dispersion in the special brass, owing to its high hardness and high wear resistance. In the present study, synchrotron X-ray radiography and rapid cooling were applied to investigate the formation mechanism of Mn₅Si₃ phase in the MBA-2 brass alloy. The primary Mn₅Si₃ phase is proved to exist stably in the alloy melt and nucleate from the melt at temperatures above 1373 K (1100 °C). In addition, the precipitation mechanism of Mn₅Si₃ phase is addressed systematically by the isothermal heat treatment. The Mn₅Si₃ particles are observed to precipitate from the matrix at temperatures above 1023 K (750 °C), and a crystallographic orientation relationship is found between the precipitated Mn₅Si₃ particle and β phase: \( (110)_{\beta } //(1\overline{1} 00)_{{{\text{Mn}}_{5} {\text{Si}}_{3} }} \) and \( [\overline{1} 11]_{\beta } //[11\overline{2} \overline{2} ]_{{{\text{Mn}}_{5} {\text{Si}}_{3} }} \). However, the precipitation of Mn₅Si₃ phase is thermodynamically inhibited at lower temperatures, which can be ascribed to the increase in the Gibbs free energy of formation of Mn₅Si₃ with decreasing the temperature.