Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 712

Full Record for Micrograph 712

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Micrograph no
Brief description
As-cast wrought-grade aluminium alloy (Al-Mg-Fe-Si containing < 1wt.% of each solute). Addition of TiB2 particles facilitates the formation of a fine, equiaxed grain structure (grain refinement).
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
Metal or alloy
Not specified
Standard codes
Sample preparation
Electrolytically etched using Barker's reagent.
Cross-polarised light microscopy
Length bar
400 μm
Further information
This micrograph illustrates one of the possible growth morphologies that a solidifying metal can adopt (c.f. micrograph 711). The grains in this structure exhibit no dendritic branching, i.e. the solid-liquid interfaces of the growing grains are smooth. When a solid grain is growing from the liquid phase, it will initially exhibit a smooth interface; such an interface can become unstable as the grain becomes larger due to rejection of solute into the liquid phase. Hence, smooth grain boundaries are associated with fine grain structures and low solute contents.

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; hence the grain structure is imaged.
T Quested
Department of Materials Science and Metallurgy, University of Cambridge
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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