The structure of rapidly solidified foil of the eutectic Sn – 8.8 wt. % Zn alloy

Abstract

Microstructure of rapidly solidified eutectic alloy foil Sn – 8.8 wt. % Zn was studied. The alloy foil consists of solid solutions of zinc and tin. Dark equiaxed dispersed precipitates of zinc solid solution are uniformly interspersed in the matrix of tin solid solution. The parameters of the microstructure were determined. The average chord of a random secant at the sections of precipitates of a solid solution of zinc is 0.33 mm, and the specific interface surface is 0.81 mm–1. The precipitations of the tin solid solution have a microcrystalline structure. Specific surface of high angle boundaries less than 1 mm–1. The texture of the precipitates of solid solutions of tin and zinc in the foil was studied, and the pole densities of the diffraction lines of these phases are presented. The tin solid solution has the texture (100), and the zinc solid solution has the (0001) texture, which is explained by the predominant growth of grains, in which the crystalline planes of (100) tin and (0001) zinc are most closely packed and perpendicular to the heat flux. Eutectic alloy Sn – 8.8 wt. % Zn is in an unstable state. Annealing the foil causes the dissolution of small and coarsening of large particles of zinc solid solution, as well as the decomposition of a supersaturated tin solid solution. These processes cause an enlargement of the microstructure: an increase in the average particle size (dZn) of a solid solution of zinc and its volume fraction (VZn), a decrease in the specific surface (S ) of interphase boundaries.

The Formation of the Structure of the Alloys of the Tin–Zinc System upon High-Speed Solidification

“…Isothermal annealing of the foils of the Sn-8.8 wt % Zn alloy at 180C induces an increase in the mean chord d Zn of the random secants on the precipitates of zinc and volume fraction of zinc and a decrease in the specific surface of the interphase boundary S IPB . For example, the volume fraction of zinc increased twofold, the average grain size increased threefold, and the specific surface decreased twofold as a result of annealing for 20 h. The changes in the parameters of dissolution of the small precipitates and enlargement of the large precipitates, which is the reason for the increase in the mean chord d Zn and the decrease in the specific surface of the interphase boundary S IPB [30]. CONCLUSIONS Thus, the fast-solidificated foils of the eutectic alloy of the zinc-tin system as well as the alloys with the composition close to the eutectic composition are characterized by the uniform distribution of the dis-persed equiaxial zinc particles and absence of its rough plates, which improves the mechanical properties of the alloy and has great practical importance.…”