Microstructure of rapidly solidified Al7.5Cu2.5Fe

Abstract

A rapidly solidified aluminium alloy of nominal composition 7.5 wt.% Cu and 2.5 wt.% Fe was investigated by transmission electron microscopy. The material was seen to have a fine, homogeneous cell structure with a high dislocation density within the cells. Interconnected particles of the iron-rich AlFeCu-type quasi-crystalline (QC) phase were found to exist on cell boundaries, coexisting with a low fraction of the tetragonal body-centered θ-Al 2Cu phase. Indications are found that the QC particles are connected through 3-fold axes. The QC is found to accomodate nearly all Fe in the alloy. An in situ heat treatment at 300 °C caused precipitation and growth of the θ-Al 2Cu phase. The Cu contents in matrix and in the QC phase were seen to decrease. No transformation or growth of the QC phase could be observed. No other phase except for the QC phase was found to contain iron in the alloy. Weak orientation relationships between the QC phase and the θ phase and between the two phases and the aluminium matrix have been found.