MICROSTRUCTURE OF RAPIDLY SOLIDIFIED ALLOY Al-1.5 WT.% Pb

Abstract

Ultra-rapid quenching from the melt makes it possible to obtain a significant refinement of the structural components of alloys, a significant increase in the mutual solubility of components during the formation of solid solutions, and the release of metastable phases. When using the ultrafast quenching method, the cooling rate of the liquid reaches 105 K/s and higher. Aluminum alloys doped with bismuth and lead can be used to generate hydrogen by their interaction with water. During ultra-fast quenching from the melt, a microcrystalline structure is formed containing dispersed precipitates of the second component. Foils of the Al-1.5 wt. % Pb alloy are obtained from a melt droplet weighing approximately 0.3 g, injected onto the inner polished surface of a rapidly rotating copper cylinder, where it spreads and solidifies into a foil. The estimated cooling rate of the melt reached 106 K/s. A cellular structure is formed in the Al-1.5 wt. % Pb foil layer adjacent to the free surface. Dispersed lead particles are located at the cell boundaries and in the cell volume. The shape of the lead particles is close to spherical, which is due to the minimum value of the surface energy of the alloy. Isothermal annealing of rapidly solidified foils of the alloy under study at 295 °C did not have a significant effect on the average diameter of lead particle cross-sections, while annealing at 400 °C caused their monotonous growth. With an increase in the annealing temperature above 400 °C, a stronger growth of lead particles located at the grain boundaries is observed than in the volume of their cells. In rapidly solidified foils of the alloy under study, a (111) texture is formed. This is explained by the fact that in the direction of heat removal, predominantly those grains grow whose {111} planes coincide with the interphase boundary and are parallel to the crystallizer surface.