Nuclear Physical Study of the Composition of Near-Surface Layers of Rapidly Solidified Foils of Al–Mg–Li–Sc–Zr Alloy after Thermal Treatment

The influence of thermal treatment on the lithium distribution over the depth of near-surface layers was 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 rotating copper drum. It was found by electron backscatter diffraction that as-cast foils had a micrograin structure with an average grain size of 12 μm and a texture [111]. Using atomic force microscopy, it was determined that the air-side surface was characterized by a fine cellular structure, which was also observed in the area of caverns and cavities on the drum-side surface. The surface roughness of the foils was from 44 to 57 nm. The patterns of the lithium depth distribution in annealed specimens were established by nuclear reaction analysis using a proton-induced reaction (p, α). It was found that during low-temperature annealing, the near-surface and deep layers of the samples were depleted in lithium, which was evenly distributed over the foil depth. A multiple increase in the lithium concentration found in the near-surface region of the foils was established during high temperature annealing, resulting in the formation of a composition-gradient foil structure. The effect of 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.