The Influence of External Mechanical Stresses on Agglomeration and Bending of Solidifying Crystals

Abstract:

The influence of external mechanical stresses on agglomeration and bending of solidifying crystals has been investigated by microstructural characterisation of hypoeutectic Al cast specimens. The samples were produced by near-static cooling, gravity die casting and high pressure die casting (HPDC), where the solidifying crystals experience different levels of mechanical stresses. Electron backscatter diffraction (EBSD) technique was used to acquire grain misorientation data which can be linked to crystal agglomeration and bending behaviour during solidification. The length fraction of low-energy grain boundaries in HPDC samples was substantially higher than in gravity diecast and ‘statically cooled’ samples. This is related to the high amount of shear applied on the solidifying alloy, which promotes crystal collisions and agglomeration. In-grain misorientations were significant only in branched dendritic crystals which were subjected to significant shear stresses. This is attributed to the increased bending moment acting on long, protruding dendrite arms compared to more compact crystal morphologies.

• Periodical: Materials Science Forum (Volumes 654-656)
• Pages: 1367-1372
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.654-656.1367
• Online since: June 2010
• Authors: Somboon Otarawanna, Christopher M. Gourlay, Hans Ivar Laukli, Arne K. Dahle
• Keywords: Coalescence, Crystal Collisions, Dendrite Bending, Grain Boundary Energy, High Pressure Die Casting (HPDC), Misorientation

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