IME Process Metallurgy and Metal Recycling, RWTH Aachen University Prof. Dr.-Ing. Dr. h.c. Bernd Friedrich Understanding of Inclusions - Characterization, Interactions and Boundaries of Removability with Special Focus on Aluminium melts Bernd Friedrich WERKSTOFFWOCHE, Dresden 14.09.2015
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IME Process Metallurgy and
Metal Recycling, RWTH Aachen University
Prof. Dr.-Ing. Dr. h.c. Bernd Friedrich
Understanding of Inclusions - Characterization,
Interactions and Boundaries of Removability with
Special Focus on Aluminium melts
Bernd Friedrich
WERKSTOFFWOCHE, Dresden 14.09.2015
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Recycling
Motivation
• Inclusion content is one of the most
important quality requirements
• They effect the mechanical properties
and formability
• They must be removed to reach
required product qualities
*Constellium
*Jaguar
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Product Defects: Straches on the Surface
Example of stringers (scratches on a rolled surface) *Constellium
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Motivation: Requirements of Metal Purity
1 ppb / 1000 ppt
10
100
10
100
1 ppm / 1000 ppb
3 ppm
ppt
ppt
ppb
ppb
Alloys
without
filtration
Extrusion
Alloys with
filtration Computer
Discs
Foil
with
filtration
Peter Waite, Light Metals 2002
Non-metallic inclusions
99,7
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Recycling
Aluminium Production
furnance treatment channel treatment
electrolysis
billet casting rolling ingot casting
melting furnance
oxides
carbides
nitrides
carbides
oxides
borides
intermetallics oxides
oxides oxides
*Trimet Aluminium SE
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Inclusions as a Part of Potential Impurities in Al-Melts
Impurities in Al-melts
Dissolved elements Inclusions
Dissolved metals
Primary: Na, Ca, Li, Mg…
Secondary: Fe, Si, Cu, Mn…
Dissolved gas
(H)
Oxides
Al2O3
MgO
MgAl2O4
SiO2
Carbides
Al4C3
TiC
SiC
Nitrides
AlN
Borides
TiB2
AlB2
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Non-metallic Inclusions
• The non-metallic inclusions can
vary from <1-500 µm
• They influence mechanical
properties and surface quality
• They can be devided into endo-
and exogeneous inclusions
Example of inclusions in a thin wall product
(wall thickness about 100 µm)
If not removed, they will appear as hole in foil,
surface defects on sheets, edge cracking in slabs
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Recycling
Inclusion Formation by Interactions with Solids
used aluminum beverage cans
(UBC scrap)
graphite crucible
with pigments (TiO2/Fe2O3)
2 Al + Fe2O3 → Al2O3 + 2 Fe(Al)
2 Al + TiO2 → Al2O3 + Ti(Al)
with refractory materials
4Al + 3C = Al4C3
Al + SiO2 = Si + Al2O3
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Type of Inclusions in Al-melts (1) - Oxides
Type Morphology Density g/cm3 Dimensions µm
Oxides
MgAl2O4 Spinel Particles, skins, flakes 3.60
Dispersoids Oxide skins
0.1-100 10-5000
Al2O3 (Corundum) Particles, skins 3.97
Dispersoids Oxide skins
0.2-30 10-5000
MgO Particles, skins 3.58
Dispersoids Oxide skins
0.1-5 10-5000
SiO2 Particles 2.66 0.5-30
CaO Particles 3.37 <5
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Type of Inclusions in Al-melts (2) – Non-oxides
Type Morphology Density g/cm3 Dimensions µm
Carbides
Al4C3 Particles, clusters 2.36 0.5-25
SiC Particles 3.22 0.5-5
TiC Particles, clusters 4.7 <5
Borides
TiB2 Particles, clusters 4.5 1-30
AlB2 Particles 3.19 0.1-3
Nitrides
AlN Particles, skins 3.26 10-50
Chlorides
CaCl2, NaCl, MgCl2 Liquid droplets 1.9-2.2 0.5-1
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Mg + 𝟏
𝒙Ox = MgO
Formation Mechanisms of Inclusions (1) – Simple Oxides
2Al + 𝟑
𝒙Ox = Al2O3
Origin: Refractory materials, atmosphere
contact with solid or liquid aluminium
Origin: Reaction between magnesium
and oxygen in the melt when the alloy
contains more than 2% Mg
W. Schneider, Filtration of Aluminum Melts
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Formation Mechanisms of Inclusions (2) – Spinell Oxide
2Al(l) + Mg[Al] + 2O2(g) → Al2MgO4(s)
2Al(l) + Mg[Al] + 2SiO2(s) → Al2MgO4(s) + 2Si[Al]
3Mg[Al] + 4Al2O3(s) → 3Al2MgO4(s) + 2Al(l)
Origin: Spinel oxides usually form in
alloys with <2% Mg content
W. Schneider, Filtration of Aluminum Melts
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Recycling
Oxidation of Al-Mg Alloys
Crucible 1
2 O2 +
Mg2+ → MgO + 2L+
L+ Mg2+
e-
MgO MgO → Mg2+ + OAl + 2e
Metal channels O
Aluminium alloy
film
2 Al + 3O → Al2O3
Bulk aluminum
alloy
*Venugopalan
Alumina
Spinel
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Continuous Inclusion Generation by Oxidation
Oxidation behaviour of aluminium melts differs from each other due to
different alloying elements.
The oxide layer of pure aluminium is stable, but Mg-containing Al2O3 layers
cause continuous oxidation of melt because of its instability.
Increasing inclusion concentration of the Mg-containing Al-alloy melt
during three experiment days.
0
10
20
30
40
50
60
70
80
90
100
Inc
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(k/k
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Day 1 Day 2 Day 3
*M. Gökelma, Master Thesis, IME-RWTH Aachen
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Formation Mechanisms of Inclusions (3) – Al-carbide
4Al + 3SiC → 3Si + Al4C3
Origin: They are formed if the solubility of
carbon is above the limit
Generation by reactions between
- melt and cathode-anode in cells
- molten metal and tools
- melt and refractory
- melt carbon from alloying elements
W. Schneider, Filtration of Aluminum Melts
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Formation Mechanisms of Inclusions (4) – Ti-boride/carbide