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

DoITPoMS Micrograph Library Full Record for Micrograph 615

Full Record for Micrograph 615

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Micrograph no
615
Brief description
Cross-section of an aluminium casting
Keywords
alloy Link to MATTER Glossary entry for alloy, aluminium Link to MATTER Glossary entry for aluminium, cast, casting, chill zone Link to MATTER Glossary entry for chill zone, columnar, equiaxed Link to MATTER Glossary entry for equiaxed, metal
Categories
Metal or alloy
System
Al
Composition
Commercial purity (99.5%)
Standard codes
Reaction
N/A
Processing
Al melt has been poured directly into a cold mould
Applications
Casting is an economical process for the net-shape forming of fairly complex components, particularly large ones such as ships propellers.
Sample preparation
Technique
Reflected light microscopy
Length bar
10 mm
Further information
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).
Contributor
Prof T W Clyne
Organisation
Department of Materials Science and Metallurgy, University of Cambridge
Date
03/10/02
Licence for re-use
Attribution-NonCommercial-ShareAlike 4.0 International