Nuclear Physics Study of the Composition of Surface Layers of Rapidly Solidified Foils of Al–Mg–Li–Sc–Zr Alloy after Heat Treatment

Abstract

Abstract: The influence of heat treatment on the distribution of lithium over the depth of surface layers is studied for rapidly solidified foils of industrial Al–Mg–Li–Sc–Zr alloy (1421) produced by ultra-rapid quenching from the molten state using unilateral cooling on the internal surface of a rotating copper drum. It is found by electron backscatter diffraction that the as-cast foils had a micrograin structure with an average grain size of 12 μm and the [111] texture. Using atomic-force microscopy, it is determined that the air-side surface is characterized by a fine cellular structure, which is also observed in the area of caverns and cavities on the drum-side surface. The surface roughness of the foils is from 44 to 57 nm. The patterns of the lithium depth distribution in the annealed samples are established by nuclear-reaction analysis using a proton-induced reaction (p, α). It is found that during low-temperature annealing, the surface and deep layers of the samples are depleted of lithium, which is evenly distributed over the foil depth. A multiple increase in the lithium concentration found in the surface region of the foils is established during high-temperature annealing, resulting in the formation of a composition-gradient foil structure. The effect of the structure and phase changes caused by the decomposition of a supersaturated solid solution with the precipitation of lithium-containing phases on the behavior of lithium in the annealing temperature range 150–380°C is discussed.