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

V G Shepelevich,D A Zernitsa

doi:10.1134/s2075113321040407

Abstract

The results of the study of the parameters of the structure of the fast-solidificated foil of hypoeutectic, eutectic, and hypereutectic alloys of the Sn–Zn system containing 4.4, 8.8, and 15 wt % Zn are presented. The fast-solidificated foil consists of equiaxial zinc particles and a supersaturated solid solution of tin. The zinc particles are uniformly distributed in the foil, which is induced by the formation of a supercooled and supersaturated liquid solution and its subsequent spinodal decomposition. The tin- and zinc-enriched regions of the liquid solution transform to crystalline phase nuclei. The volume fraction of zinc particles, the mean chord of the random secants on the sections of the zinc particles, and the specific surface of the interphase boundary formed by zinc and tin increase with the increase in the concentration of zinc in the alloys under study. The foil of the Sn–Zn alloys has a microcrystalline structure, in which crystallographic texture of the grains is observed. The formation of the (100) texture of tin and (0001) texture of zinc is observed. The fast-solidificated foils of the alloys are in an unstable state, which leads to the decomposition of the supersaturated solid solution, dissolution of small particles, and growth of large particles. Annealing at 180°C for 22 h induces an increase in the mean chord of the sections of the zinc particles and volume of the zinc particles and a decrease in the specific surface of the interphase boundary.

Highlights

Achieving a reliable soldered joint without using harmful lead-based additives prohibited by the Restriction of Hazardous Substances (RoHS) Directive of the Council of Europe [1] is possible owing to tin–zinc alloys that find wide application in industry [2]
A eutectic Sn–Zn solder is of interest because of its low melting point (198.5 C) which is close to that of a tin– lead alloy (183 C) [3, 4] and higher microhard-ness and tensile strength, which is confirmed by the results of the tests of the alloys of the Sn–Zn system obtained at low rates of cooling [5, 6]
Isothermal annealing of the foils of the Sn–8.8 wt % Zn alloy at 180 C induces an increase in the mean chord dZn 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 SIPB

Summary

INTRODUCTION

Achieving a reliable soldered joint without using harmful lead-based additives prohibited by the Restriction of Hazardous Substances (RoHS) Directive of the Council of Europe [1] is possible owing to tin–zinc alloys that find wide application in industry [2]. Despite a whole series of studies of the alloys of the binary Sn–Zn system obtained at low and medium rates of cooling, study of the foils of Sn–Zn alloys with various concentrations upon high-speed solidification is scarce in the published sources. In this connection, the investigation of the structure of the foils of the Sn–Zn alloys obtained at ultrahigh rates of cooling is relevant and is of scientific and practical importance. The annealing of the foils was performed in a drying oven

RESULTS AND DISCUSSION

Fractio n

Parameters of the grain structure

CONCLUSIONS