Microstructure characterization of electro-chemically activated aluminium
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Microstructure characterization of electro-chemically activated aluminium Yingda Yu 1 , Øystein Sævik 1 , Jan Halvor Nordlien 2 and Kemal Nisancioglu 1 1 Department of Materials Technology, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway 2 Hydro Aluminum R&D Materials Technology, N-4256 Håvik, Norway Light Metal Surface Science
description
Light Metal Surface Science. Microstructure characterization of electro-chemically activated aluminium. Yingda Yu 1 , Øystein Sævik 1 , Jan Halvor Nordlien 2 and Kemal Nisancioglu 1 1 Department of Materials Technology, Norwegian University of Science - PowerPoint PPT Presentation
Transcript of Microstructure characterization of electro-chemically activated aluminium
Microstructure characterization of electro-chemically activated aluminium
Yingda Yu1, Øystein Sævik1, Jan Halvor Nordlien2 and Kemal Nisancioglu1
1Department of Materials Technology, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway
2Hydro Aluminum R&D Materials Technology, N-4256 Håvik, Norway
Light Metal Surface Science
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Background
In our Electrochemistry group, a long history to investigate the Al anodic activation phenomenon by high temperature annealing.
This curious anodic activation is found to be related with the segregation of the trace element lead (Pb) at the alloy surfaces.
This activation mechanism has not been fully explained, even though this phenomenon has long been exploited for practical purposes.
The objective of the present work is to provide further microstructure evidence for understanding this Al anodic activation phenomenon.
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0.0001 0.001 0.01 0.1 1 10 100
Current density [mA/cm2]Po
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VSC
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As extruded
10 min
30 min
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High temperature annealing leads to electrochemical activation as indicated by corrosion potential (1) and polarization measurements (2).
(1) measured in acidified sea water after AA 3102 heat treatment at different temperature for 2h.
(2) measured in 5% NaCl solution after AA 3102 heat treatment at 600ºC for different annealing time.
JTB Gunderson PhD Thesis NTNU2002
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Pote
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As extruded
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600°C
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The 50ppm Pb-Al binary model alloy after high temperature heat treatment in air is used in the present investigation for understanding the Pb segregation on Al surface.
GD-OES depth profiles suggested the electrochemical activation is related to the enrichment of the trace element Pb at the oxide-metal interface.
JTB Gunderson PhD Thesis NTNU2002
GD-OES depth profiles for AA3102 heat-treated for 60 min at 600°C
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10 nm
(111)(100) The results reported at the 2002 LMSS annual meeting
(111
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(111)(100)
Even though, no Pb particles were found in the surface region, TEM EDS analyses indicated the increasing Pb segregation at the metal-oxide interface with increasing annealing time.
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Experimental
Sample Detail50ppm Pb-Al model system, 600ºC annealing for 1 hr, 2hr and 4hr
TEM observation
Philips CM30 operated at an accelerating voltage 300 kV
TEM sample preparation
Cross-sectional samplescut to slice ground to 150 m dimpled to about 30 m ion beam thinning at 3-3.5 degree 3.5 kV (PIPS)
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Where are the Pb-containing particles distributed?
Pb-containing particles are segregated at the metal-oxide interface.
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EDS micro-probe composition analysis
Even though the particle size with only 5 nm in diameter, it can emit strong enough TEM EDS peaks, both for Pb L and Pb M.
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Pb-containing particles are in metallic form
HRTEM investigation reveals that the fringe distances of the Pb-containing particles are around 0.286 nm which close to Pb (111).
Moreover, by using the -Al2O3 as the internal reference, the particle lattice distance can be exactly determined as 0.286 nm that suggests these particles are in metallic state.
-Al2O3
Al Matrix
Al Matrix
Al Matrix
0.286 nm
0.286 nm0.286 nm
0.286 nm0.453 nm
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Lattice parameters of all possible Phases
0.291 nm(106)
0.278 nm(210)
0.276 nm(111)
PbAl12O19 Hexagonal
a = 0.555 c = 0.219nm
0.286 nm(111)
0.248 nm(200)
Pb FCC Cubica = 0.494 nm
0.453 nm(111)
0.277 nm(202)
0.236 nm(133)
-Al2O3 FCC Cubica = 0.784 nm Spinel
0.234 nm(111)
0.203 nm(200)
Al FCC Cubica = 0.405 nm
The lattice planes and distances related with the present HRTEM investigation
-- -
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How to be related with surface activation?
The particle shapes are supposed not change too much under TEM beam since they are embedded inside the sample.
Even though the elliptic shaped particles were sometimes detached from the interface, their surfaces facing the metal interface were flat, indicating that these particles were originally located at metal-oxide interfaces.
Epoxy
Oxide
Al MatrixAl Matrix
Interface
Al MatrixAl Matrix
InterfaceInterface
Oxide
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Particle size effect – inversely proportional to nano-particle size – lower the melting point
Melting Point depression of the embedded nano-particles
The particle with no orientation relationship between Pb /Al interface is more unstable that that with semi-coherent interface under electron beam irradiation.
Understanding the interface state is important to reveal Pb activation behaviour
Poor WettingGood Wetting
first TEM investigation (Takagi J. Phys. Soc. Jap.1954)
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Conclusions
Small Pb particles of the order 10 nm in size were detected and originally located at the metal-oxide interface.
The particles are metallic Pb based on lattice fringe measurement and thermodynamic considerations.
The initial HRTEM results reveal that these nano-particles are randomly oriented with incoherent interfaces with neighbouring alumina and aluminium.
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Acknowledgments
Light Metal Surface Science is funded by:The Norwegian Research
Council• DuPont Powder Coatings • Electro Vacuum AS • GSB • Jotun Powder Coatings AS • NORAL AS • Norsk Industrilakkering AS• Profillakkering AS
An industry consortiumconsisting of:
Hydro Aluminium
