Morphological Characteristics of Al ₃SC Particles and Crystallographic Orientation of Al ₃Sc/Al Interface in Cast Al-Sc Alloy

Abstract

As a new type of grain refiner, rare earth element Sc has a strong grain refining effect on the microstructure of cast aluminum alloys. During the solidification process, the precipitation of Al₃Sc primary particles in the molten metal act as heterogeneous nucleation cores, promoting Al nucleation, and greatly increasing the nucleation rate. In this paper, single Al₃Sc particle and multiple Al₃Sc particles cluster are extracted by the focused ion beam, and the whole and internal structure of the particles are systematically studied using scanning electron microscope and high-resolution transmission electron microscope. The study found that under the influence of strong anisotropy, the primaryAl₃Sc particles have different growth rates in different crystal planes, and finally form a special morphological feature -a cubic shape as a whole and a "funnel-shaped" structure in part. The (111) and (110) planes of Al₃Sc particles form a coarse dendrite structure, and a large number of fine rod-shaped structures appear on the (100) plane, the Al matrix is interposed between the rod-shaped structures. At the interface between Al₃Sc and Al matrix, two crystallographic orientation relationships were observed. At the same time, a special pseudomorphic solid layer was observed at the interface between Al and Al₃Sc particles. In addition to individual Al₃Sc particles, it was also found that some Al₃Sc particles grow in a nucleus at the same time and have the symmetrical morphology of rotating twins.

Keywords: Al3Sc particles, grain refinement, anisotropy, pseudomorphic solid layer, Crystallographic orientation relationship