Nuclear physics study of the composition of surface layers of rapidly solidified foils of Al–Mg–Li–Sc–Zr alloy after heat treatment

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.