Full Record for Micrograph 56

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Micrograph no
Brief description
Al 96, Cu 4 (wt%), solution treated and overaged - precipitation hardening
alloy Link to MATTER Glossary entry for alloy, aluminium Link to MATTER Glossary entry for aluminium, copper, metal, metastable Link to MATTER Glossary entry for metastable, overaged Link to MATTER Glossary entry for overaged, precipitation Link to MATTER Glossary entry for precipitation, precipitation hardening Link to MATTER Glossary entry for precipitation hardening, quenching Link to MATTER Glossary entry for quenching, solution heat treatment Link to MATTER Glossary entry for solution heat treatment
Metal or alloy
Al-Cu   Link to phase diagram
Al 96, Cu 4 (wt%)
Standard codes
Solution treated and over-aged
Sample preparation
Reflected light microscopy
Length bar
200 μm
Further information
This sample has been aged after quenching to enable the growth of precipitates from a supersaturated solid solution. The strength of the alloy has been greatly improved by precipitation hardening. A precipitation sequence is observed eventually resulting in the formation of the stable θ phase through a series of metastable intermediates. The θ phase is an intermetallic compound with a composition close to CuAl2. The θ precipitates preferentially form on Al grain boundaries, as these are excellent heterogeneous nucleation sites. The depletion of Cu near the boundaries to these precipitates is one reason for the formation of adjacent precipitation free zones (PFZ).
Prof T W Clyne
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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