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3D Atom probe investigation of the nanostructure
of a commercial 6061 aluminium alloy processed by
SPD.
X. Sauvage1, G. Nurislamova1, M. Murashkin2, R.
Valiev2
1. Groupe de Physique des Matériaux - UMR CNRS
6634 - University of Rouen (France) 2. Institute
for physics of advanced materials, Ufa State
Aviation Technical University, Ufa, Russia
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Introduction
6061 aluminium alloy are age hardenable
Solution treatment / water quenched Artificially
aged ( T6 typically 8h at 448K )
(010) Al
High density of needle shaped b precipitates
(aligned along (001)Al ) High yield stress
(001) Al
40 nm
S.J. Andersen, Acta Mater 46 (1998) 3283
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Introduction
6061 aluminium alloys processed by ECAP from
W.J. Kim and co-authors, Met Trans 33A (2002)
3155
6061 alloy solutionized, water quenched and
processed by ECAP
Standard ageing treatment after water quenching
(T6)
Why the hardness of the material processed by
ECAP is higher than the hardness after standard
ageing treatment ?
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Introduction
Ageing after ECAP from W.J. Kim, Met Trans 33A
(2002) 3155
Why a low temperature ageing after ECAP leads to
further increase of the hardness ?
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Investigated material
Material composition Mg Si
Cu Fe Cr Mn wt. 0.8 - 1.2 0.4 - 0.8
0.15 - 0.4 0.7 0.15-0.35
0.15 Solid solution treatment 1h at 803K
followed by water quenching ECAP processing 4
passes, 383 K, route Bc, 90 angle, 10
mm/s Post-ECAP low temperature ageing treatment
24h at 403 K
Tensile test experiments and investigation of the
nanostructure by three-dimensional atom probe
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Mechanical properties
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Solution treatment ageing (T6)
Mg
10 nm
High density of nanoscaled b precipitates
short needles aligned along (001)Al directions
S.J. Andersen, Acta Mater 46 (1998) 3283
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Solution treatment ageing (T6)
Filtered image (regions with more than 5 at. Mg)
Si Mg Cu
10 nm
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Solution treatment ageing (T6)
Compositionprofile across a b needle
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Solution treatment ECAP
Mg
5 nm
Small spherical precipitates ( average diameter
3 nm )
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Solution treatment ECAP
Composition of precipitates 11-20 at. Mg Mg /
Si 2 1-2 at. Cu
Higher Mg / S i ratio than b precipitates of
the T6 state
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Solution treatment ECAP
Mg
13
Solution treatment ECAP ageing
Mg
5 nm
Similar spherical nanoscaled particles
Composition of particles 13-20 at. Mg Mg / Si
2 1-2 at. Cu
Size of particles diameter 3 nm
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Summary of experimental data
During ECAP at 383K - Precipitation of
spherical nanoscaled b precipitates
(smaller than b of the T6 state) -
Segregation of Cu and Mg along planar defects (GB
?)
Significant contribution to the high yield stress
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Precipitation during ECAP processing
1. Atomic mobility promoted by SPD - SPD
induced vacancies M.J. Zehetbauer, Mat Sci Forum
503 (2006) 57 - Pipe diffusion R.C. Picu,
Acta Mater 52 (2004) 161
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Conclusions

• The high yield stress of 6061 alloys processed
  by ECAP is partly attributed to the high density
  of nanoscaled b precipitates.
• SPD induced vacancies and dislocations promote
  the precipitation kinetics in 6061 alloys.
• Because of the competition between dissolution
  and precipitation, the processing temperature is
  probably a key parameter controlling the final
  mechanical properties of age hardenable aluminum
  alloys processed by ECAP.