Influence of variations in the chemical composition of LS59-1 type brasses on the nature of their calculated equilibrium phase diagrams

The paper presents calculated equilibrium phase diagrams of multi-component lead brasses of the LS59-1 type, in which the amount of both the main components (Zn, Pb) and impurities (Fe, Al, Si, etc.) varied. The thermodynamic phase equilibrium in Cu-Zn alloys, which form the basis of LS59-1 brass, was determined by using the FTLite database and the FactSage 8.0 (and later versions) thermochemical software package, which allows calculating conditions for multiphase, multicomponent equilibrium. It was found that in the equilibrium state in these alloys, β-, α-solid solutions with BCC and HCC lattices, respectively, as well as a liquid solution based on fusible lead are present as the main phases; moreover, the amount of β-phase decreases, and α-phases increases with decreasing temperature. The impurities are partially dissolved, more often in the BCC phase. In addition, solid and brittle particles of non-metallic inclusions formed during crystallization are formed on their basis. With an increase in the content of lead and impurities, the solidus temperature decreases very noticeably. The obtained equilibrium diagrams provide useful information when analyzing the processes and structure of industrial alloys. Thus, with nonequilibrium crystallization, the temperature of the end of crystallization decreases more significantly, which must be taken into account when assigning a hot deformation mode. Phase and structural compositions of the studied brasses at 730 °C in the equilibrium state and cooled after hot forging from the same temperature in industrial conditions do not coincide not only quantitatively, but also qualitatively. In the first case alloys no. 1 and 5 are two-phase - (α + β), the others (no. 2, 3, 4) are single-phase with β-structure. In the finished products the material no. 2 is α-brass, the other alloys are two-phase.