Changes of structure and microhardness during the annealing of an aluminium-tin supersaturated solid solution

Abstract

Structural and microhardness changes in an A1-0-26 at.-% Sn alloy quenched from the melt and annealed are presented. The experiments show that solid solution of 0-26 at.-% tin in aluminium, as seen in an electron microscope, can be obtained by means of rapid quenching from the liquid state. The kinetics and morphology of structure transformations are discussed in terms of vacancy-solute interactions in which clusters are formed through coagulation of Sn-vacancy couples. Growth of precipitates is explained by the ‘vacancy pumping’ model. The result of the clustering process is a structure containing spheroidal precipitates of β-tin, accommodated without strain in the aluminium matrix with definite crystallographic orientation relationships. The observed high transformation rate is attributed to the influence of an extra concentration of quenched-in vacancies which are assumed to be retained in the alloy bound to tin atoms as a consequence of their known high mutual binding energy.