Structural features and properties of the Sn-Zn-Si-Al system alloys obtained by the method of rapid solidification from the melt

The article presents the results of studying the microstructure of rapidly solidified foil of Sn55,18Zn44,50Si0,23Al0,09 alloy. The phase composition of rapidly solidified foil was studied. A uniform distribution of alloying silicon and aluminum in tin in the form of a solid solution was established. The formation of the (100) texture of tin and (10 (1) over bar0) of zinc was revealed, associated with the predominant growth of crystallites, in which the close-packed planes of tin and zinc are perpendicular to the direction of heat removal during crystallization. An analysis of the structure and properties of the foil during isothermal annealing and natural aging was performed, with a description of the processes occurring. Formation of a dispersed structure due to high degree of supercooling of liquid phase with increase of degree of dispersion of zinc during isothermal annealing (average chord d on sections of zinc phases is 1,24 mu m before heat treatment and 0,42 mu m after isothermal annealing for 170 min at 150 degrees C) along with invariance of texture during heat treatment is established. Change of the microhardness of foil during natural aging, noticeable formation of large number of clusters of precipitations of tin and zinc phases due to their supersaturation, as well as reinforcing action of alloying elements (Si, Al ) are explained. During heat treatment zinc dissolves in the matrix phase, with decrease of its volume, while share of softening phase of tin increases which leads to a decrease in the microhardness.