Tag-and-Trace Method of α-Al Crystals Applied to Study Solidification and Casting of Aluminum Alloys

Abstract

In this study, a new tag-and-trace method of α-Al crystals was developed and used to study the dissolution of a rotating Al-3Si-0.15Ti cylinder immersed into a superheated commercial purity aluminum melt. The developed tag-and-trace method consists of tagging the primary crystals of an alloy with the microsegregation of a peritectic forming solute element, e.g., titanium in aluminum alloys. During solidification, the primary crystals form with a high concentration of the peritectic forming solute, decreasing in the adjacent growth regions of the same crystal. After solidification, the solute microsegregation tag in the interior of the primary crystals can be revealed by color etching. In this work, an Al-3Si-0.15Ti cylinder with all the primary α-Al crystals tagged with titanium was immersed into a superheated titanium-free aluminum alloy. The superheat was varied, and all samples were quenched 10s after immersion of the cylinder. The tagged α-Al crystals from the original cylinder could be distinguished from the non-tagged α-Al crystals formed in the thermally undercooled region surrounding the cylinder and during quenching. Indications of liquid penetration were observed in some α-Al crystals, which indicates that disintegration of α-Al crystals may occur during stirring of the alloy cylinder into a superheated alloy.