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Full Record for Micrograph 711

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Micrograph no
711
Brief description
As-cast wrought-grade aluminium alloy (Al-Mg-Fe-Si containing < 1wt.% of each solute). No addition of grain refinement particles (e.g. TiB2).
Keywords
alloy Link to MATTER Glossary entry for alloy, aluminium Link to MATTER Glossary entry for aluminium, anodising Link to MATTER Glossary entry for anodising, dendrite Link to MATTER Glossary entry for dendrite, equiaxed Link to MATTER Glossary entry for equiaxed, iron, magnesium, metal, silicon Link to MATTER Glossary entry for silicon
Categories
Metal or alloy
System
Al-Mg-Fe-Si
Composition
Not specified
Standard codes
Reaction
Processing
As-cast
Applications
Sample preparation
Electrolytically etched using Barker's reagent.
Technique
Cross-polarised light microscopy
Length bar
1 mm
Further information
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.
Contributor
T Quested
Organisation
Department of Materials Science and Metallurgy, University of Cambridge
Date
20/01/03
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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