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

DoITPoMS Micrograph Library Micrograph 157 and full record

Micrograph 157 and full record

Link to image file for micrograph 157
Micrograph no
Brief description
Roll-bonded aluminium alloy diffusion couple annealed for 60 minutes at 600ºC.
alloy Link to MATTER Glossary entry for alloy, aluminium Link to MATTER Glossary entry for aluminium, diffusion couple Link to MATTER Glossary entry for diffusion couple, metal, recrystallisation Link to MATTER Glossary entry for recrystallisation, roll-bonding Link to MATTER Glossary entry for roll-bonding
Metal or alloy
Al, Fe 0.5, Mn 1.0 / Al, Si 1.0 (wt%)
Standard codes
Mechanical roll-bonding followed by annealing at 600ºC for 60 minutes
The couple was made to investigate diffusion of silicon through the Al-0.5Fe-1.0Mn (wt.%) alloy during annealing.
Sample preparation
Electrolytically etched using Barker's reagent.
Cross-polarised light microscopy
Length bar
750 μm
Further information
This micrograph shows the grain structure of a roll-bonded aluminium alloy diffusion couple annealed for 60 minutes at 600ºC. The upper half of the couple is Al-0.5Fe-1.0Mn (wt.%), the lower half is Al-1.0Si (wt.%). Annealing has recrystallised the microstructure. The Al-Fe-Mn alloy has many intermetallic particles (the dark phase). These help create recrystallisation nuclei, hence this alloy has a high density of small grains relative to the Al-Si alloy.

The Barker's etch produces 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. Strain of the aluminium matrix during rolling around the intermetallic particles in the Al-Fe-Mn alloy produces a high density of dislocations. Because recovery of the dislocations creates nuclei for recrystallisation, this high defect density results in a much finer recrystallised grain structure than in the particle-free Al-Si alloy.
D T L Alexander
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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