The Influence of High-Temperature Heat Treatment on the Evolution of Surface Composition of Rapidly Solidified Foils of Al–Mg–Li–Sc–Zr Alloy

Abstract

The influence of high-temperature annealing on the composition of surface layers of rapidly solidified Al–Mg–Li–Sc–Zr alloy foils of 1421 grade obtained by centrifugal quenching from the melt has been studied when heated to 380°C in air depending on the holding time. Surface elemental mapping of the foils annealed for 1 h was carried out by scanning electron microscopy with energy dispersive X-ray microanalysis. The depth distribution of lithium after annealing the samples for 1, 2, and 8 h was studied by nuclear reaction analysis. After short-term annealing for 1 h, the formation of a gradient composition with an increased content of the main alloying elements in the surface layers of annealed foils was found. The thickness of the diffusion layer enriched with lithium is about 3.3 μm. In the 0.3-μm-thick near-surface layer, the average lithium concentration is 30 at %. In contrast to the contact surface, the nonmonotonic character of the lithium concentration profiles of the foils near the free surface includes the presence of a sharp maximum at a depth of 0.3 μm: the lithium content increases from 20 at % in the thin surface layer (0.1 μm) up to 40 at %. During the annealing process, with increasing holding time, an intensive mass transfer of lithium atoms to the depth of the foils is observed. The thickness of the diffusion layer increases 4 times.