Crystal orientation relationships and pattern evolution in directionally solidified Al-Cu-Mg ternary eutectic

Abstract

Understanding the mechanisms of microstructure evolution during alloy solidification is crucial in designing multi-phase, multi-component systems. In the current work, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques are deployed to carry out a detailed experimental investigation to better understand the correlation between crystallographic orientation relationships (ORs) and the microstructural pattern evolution of directionally solidified Al-Al2Cu-Al2CuMg ternary invariant eutectic. The behavior of the patterns in response to imposed low (6 K/mm) and high (25 K/mm) thermal gradients is also presented. Close examination of the microstructure revealed an unexpected modification of lamellar growth, with lamellar sheets being limited in length to approximately four times the width of one sheet, and the Al2Cu rod phase aligning along these pre-existing boundaries which correspond to low index crystallographic planes. Alignment of the pattern was found to increase with increasing thermal gradient. The results shed more light on somewhat contradictory literature data and provide an increased understanding of pattern evolution in multi-phase eutectic systems.