Grain misorientation in thixo-billets prepared by melt stirring

Abstract

For semi solid metal (SSM) slurries, in addition to the morphology, size, distribution and percentage of the solid phase particles, the microstructure of individual solid particles is another important parameter to be considered. This is particularly an issue when SSM billets are prepared by continuous stirring of the melt to temperatures below liquidus, as in the case of electromagnetic stirring of Al-Si alloys. Microstructural evolution of the electromagnetically stirred Al-Si alloy is investigated by means of optical and electron microscopy. Electron backscatter diffraction (EBSD) analysis of the stirred and unstirred cast billets has shown stirring to generate local misorientation within individual solid particles. This is an indication of growing dendrites undergoing plastic deformation during the course of SSM slurry preparation. The formation of dislocations and their subsequent rearrangement into subgrain boundaries has been shown by EBSD analysis and TEM studies of thin foil specimens respectively. © 2009 Elsevier Inc. All rights reserved.