Different grain morphologies in grain-refined 7075 billet

Abstract

Different grain morphologies are identified in the central portion of a direct-chill cast, grain-refined 7075-alloy billet, i.e. coarse-cell and fine-cell dendrite grains and grains that are less developed than the bulk of the structure. Three-dimensional reconstruction of a representative volume is used for separating these distinct grain types. Microsegregation measurements show that coarse-cell grains are depleted of solutes (Cu, Mg, Zn), whereas fine-cell grains and less developed grains are enriched in solutes. Analysis of non-equilibrium solidification demonstrates that the observed grain types could be formed in different stages of solidification and correspondingly in different parts of the billet sump. Coarse-cell grains nucleate in the upper part of the sump, whereas fine-cell grains and less developed grains originate from deeper portions of the sump.