Cross-section of an aluminium casting

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Description:	Solidification initiates on the mould walls because this is where the melt is coolest and because inhomogeneities promote nucleation. Selective growth then occurs, whereby the grains which have their easy growth direction <100> parallel to the heat flow direction grow fastest, and cut off the paths of less well-aligned grains. This results in a 'columnar zone' which may extend to the centre of the casting but often gives way to an 'equiaxed zone'. The equiaxed grains may result from sedimentation from the free surface, from the detachment of dendrite tips, or simply from heterogeneous nucleation ahead of the advancing front (though the latter is only likely if deliberate 'melt inoculation' has been implemented).
Keywords:	alloy • aluminium • cast • casting • chill zone • columnar • equiaxed • metal
Categories:	Science approaches > Microstructure Materials > Metals & alloys > Aluminium & alloys Processes > Shaping > Casting Testing, analysis & experimentation > Metallography Scale > Micro
Created by:	Prof T W Clyne, Department of Materials Science and Metallurgy, University of Cambridge DoITPoMS, University of Cambridge
Published by:	DoITPoMS, University of Cambridge
License:	This resource is released under the Creative Commons Attribution Non-Commercial Share Alike license (2.0 UK: England & Wales). You are free: to share – to copy, distribute and transmit the work to remix – to adapt the work Under the following conditions: attribution – You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). noncommercial – You may not use this work for commercial purposes. share alike – If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one. View the full legal code here.
Date created:	03 October 2002
Date added:	21 August 2009
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Resource ID:	1648
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