Image icon  As-cast wrought-grade aluminium alloy

 
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Description: The micrograph shows Al-Mg-Fe-Si containing < 1wt.% of each solute. No addition of grain refinement particles (e.g. TiB2). This micrograph illustrates one of the possible growth morphologies that a solidifying metal can adopt (c.f. micrograph 712). The dendritic structure is the result of instabilities in the solid-liquid interface during growth due to the rejection of solute into the liquid phase. Dendritic grains are more prevalent in alloys of high solute content and larger grain sizes.

The Barker's etch and applied electrical field produce a thick oxide layer on the grains of aluminium (anodising). When viewed in cross-polarised light, interference in the oxide layer produces colours which depend on grain orientation and oxide thickness; hence the grain structure is imaged.
Keywords: alloy • aluminium • anodising • dendrite • equiaxed • iron • magnesium • metal • silicon
Categories: Science approaches > Microstructure
Materials > Metals & alloys > Aluminium & alloys
Processes > Shaping > Casting
Testing, analysis & experimentation > Metallography
Scale > Micro
Created by: T Quested, 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).
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Date created: 20 January 2003
Date added: 21 August 2009
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Resource ID: 1740