Seminars Archive

Characterization of the evolution of internal architecture in AlMgSi alloys by synchrotron tomography

Abstract
Tomographic characterization of multiphase materials allows to determine microstructural parameters which cannot be investigated properly by two dimensional methods. These parameters, like volume fraction, connectivity, contiguity etc., affect the mechanical properties and therefore they play a vital role in the behaviour of the material. The mechanical properties of the materials can be changed through modifying the internal architecture by varying the casting parameters or in some cases applying a heat treatment on the solidied microstructure. Two types of alloys with different Mg and Si contents have been investigated, above and below the stochiometric ratio of Mg2Si. For the alloy with low Mg and high Si content an additional eutectic solidication takes place at 558 C. The remaining melt freezes as an alpha-Al/Mg2Si/Si triple eutectic. Synchrotron tomography was carried out at the ID19 and ID22NI beamlines of the European Synchrotron Radiation Facility to investigate the effect of solution treatment on the architecture formed by the Mg2Si, Si and alpha-aluminium. The same sample was imaged in as cast and in heat treated conditions, revealing the structure with a spatial resolution of 1 micron and 0.18 micron, respectively. The sequence of solidification and the formation of the microstructure was studied in situ at the ID15B beamline using a fast imaging setup. After three dimensional image processing and image analysis, the eutectic phases and the alpha-aluminium dendrites were characterized and the results were correlated with the mechanical behaviour of the alloys.