Friction Stir Welding

1st IPSUS Progress Meeting, HASYLAB @ DESY, Hamburg 2007
Microstructure characterisation of
Dissimilar Al to Steel
Friction Stir Welds
Aleksander Kostka
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
MATERIALS DIAGNOSTICS
AND STEEL TECHNOLOGY
Outline
¾ Introduction
¾ Materials
¾ Current results
¾ Planned work
¾ Results example
Max-Planck-Insitut für Eisenforschung GmbH
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Motivation
Friction Stir Welding – FSW
9
9
9
9
Solid state process
No arc or reflection
Low distortion
Environment friendly
FSW by RIFTEC Gmbf
Difficulties of Al-alloy to Steel welds:
9 Complex brittle intermetallics
9 Considerable magnitude of
hallenges:
C
thermal stresses
9 New welding technology
9 Lack of microstructure
information
Introduction
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Scientific objectives of VI-IPSUS
¾ Viscous flow and diffusion processes in
high speed FSW
¾ Recrystallisation Kinetics in FSW
¾ Precipitation Phenomena in FSW
¾ Phase formation/transformation in FSW
Introduction
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Running tasks
¾ Task 1.1 Base material procurement & characterization
¾ Task 1.4 Preliminary mechanical and metallurgical
testing
¾ Task 3.2 Precipitation and recrystallization phenomena
in FSW
¾ Task 4.1 Deformation Mechanisms
Introduction
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Production of TWIP steels
¾ Casting
¾ Hot rolling followed by air cooling
¾ Cutting
¾ Cold rolling
¾ Heat treatment
Base materials
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Chemical composition
Sample
%C
%Al
%Mn
%Si
%Ti
V60/124 TRIP
0.1
-
1.52
1.46
0.03
V60/125 TWIP
0.05
2.85
24.7
3.02
-
V60/126 TWIP
0.63
-
22.0
-
-
V60/124 TRIP
V60/125 TWIP
V60/126 TWIP
Base material characterization
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
111
001
101
V60/126 TWIP
Average grain
size
(diameter)
48µm
8
200 µm
Base material characterization
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
111
001
V60/126 TWIP
101
Presence of nano-twins
50 µm
Specific grain boundary
definition strongly
necesesary!
Base material characterization
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
Using definition of boundaries
between identified grains
(Correspond to twin boundary 60°)
Base material characterization
V60/126 TWIP
Grains misorientation
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
subgrains nanotwins
When all boundaries are taken to
account
Base material characterization
V60/126 TWIP
Grains misorientation
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
111
001
101
V60/125 TWIP
Average grain
size
(diameter)
64µm
8
200 µm
Base material characterization
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Nearest future
9 Continuation of the SEM/EBSD analyze of the microstructure of
the TWIP and TRIP samples
- Grain size evaluation (in a proper way)
- Texture analyse
9 Preliminary mechanical and metallurgical testing:
- Analyze of the deformation mechanisms (EBSD, TEM)
- Fracture analyze (EBSD, TEM)
9 Precipitation and recrystallization phenomena in FSW
- EBSD measurements and analyse
- Specimens preparation for TEM
… more characterization
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
EMAT, Antwerp, Belgium
End of part one
Friction Stir Welding
High-strength Steel
and
Aluminium alloy
Rodrigo S. Coelho1
A. Kostka1, S. Sheikhi2, J. Dos Santos2, A. Pyzalla1
1 Max-Planck-Insitut
für Eisenforschung GmbH, Düsseldorf, Germany
2 GKSS Research Centre GmbH, Geesthacht, Germany
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Motivation
of weld light metal
Necessity
alloys to steel:
9 Reduce weight
9 Minimize fuel consumption
9 Restrict emissions
Corvette Z06
Light-Weight Structures
Aluminium alloys + Steel
Introduction
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Difficulties of Al-alloy to Steel welds:
9 Complex brittle intermetallics
9 Considerable magnitude of
thermal stresses
Friction Stir Welding – FSW
9
9
9
9
Solid state process
No arc or reflection
Low distortion
Environment friendly
Introduction
Challenges:
GKSS FSW tricept® 805 workstation
Motivation
9 New welding technology
9 Lack of microstructure
information
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
The aim
¾ Microstructure characterization:
Systematic investigations of the microstructure
evolution associated with joining of dissimilar
materials (Al-alloys to steel)
¾ Relationship between
mechanical properties
microstructure
Introduction
and
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
FRICTION STIR WELDING
Single overlap
Al-alloy to Steel
Rotation Speed (rpm)
Travel Speed (mm/sec)
Down-force (kN)
1600
6
5
Characterization
Mechanical properties
Hardness test
Shear test
Microstructure
OM
SEM - EBSD
TEM
Experimental details
4 mm
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
FRICTION STIR WELD
Optical microscopy:
9 Complex weld zones
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
FRICTION STIR WELD
Scanning electron microscopy - SEM
AA6181-T4
Retreating side
Advancing side
ZStE340
400 µm
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Mix-SZ
ZStE340
Fe-TMAZ
Fe-HAZ
Fe-BM
10 µm
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
ZStE340
Mix-SZ
2 µm
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
ZStE340
Mix-SZ
4 µm
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
ZStE340
Mix-SZ
1 µm
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
¾ Material flow
¾ Grain size analysis
¾ Local texture
111
001
1
101
AA6181-T4
2
3
ZStE340
Al
Texture Analysis
Fe alpha
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
¾ Material flow
111
AA6181-T4
2
3
001
101
ZStE340
Iron - Alpha
Aluminium
2
3
100 µm
100 µm
Texture Analysis
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
¾ Grain size analysis
¾ Local texture
001
1
9.3 µm
111
Al-SZ
101
AA6181-T4
Al-TMAZ
ZStE340
Al-HAZ
Al-BM
Al-BM
Cube recrystallization
texture
Texture Analysis
150 µm
16 µm
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Electron Back Scattered Diffraction
9.3 µm
AA6181-T4
2
ZStE340
¾ Strong texture
variation
¾ Uniform grain size
111
001
Al-SZ
101
AA6181-T4
¾ Strong grain size gradient
ZStE340
5.7 µm
Fe-BM
γ - fibre {111}║ND texture
Texture Analysis
Fe-BM
100 µm
0.3 µm
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
10 µm
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
STEM HAADF: material flow, precipitation
500 nm
500 nm
¾ Mechanical mixing
¾ Steel material flow
¾ Precipitation process occurs in the
aluminium alloy
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
STEM HAADF: intermetallic compound
500 nm
100 nm
¾ Formation of elliptical grains,
characteristic for formation of FeAl3
¾ Cracking of the intermetallics at the
mixing zone
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
TEM BF: fine grained intermetallic phase
1.17 Å
2.14 Å
3.79 Å
2.02 Å
2.43 Å
1.46 Å
1.43 Å
0.76 Å
200 nm
200 nm
Fe2 Al5
Fe alpha
¾ Intermetallic phase – steel interface
Microstructure
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Micro Hardness Test
AA6181-T4
Mix-SZ
Fe-HAZ
Fe-TMAZ
800 µm
ZStE340
Al-SZ
ZStE340 - Steel
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Micro Hardness Test
ZStE340 - Steel
AA6181-T4
AA6181-T4
800 µm
ZStE340
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Overlap Shear Test
Maximum loading
AA6181-T4
FSW Al-steel
4330 N
3318 N
73% efficient
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Fractography Analysis
2
3
1
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Fractography Analysis
1
0.5 mm
50 µm
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Fractography Analysis
1
0.5 mm
50 µm
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Fractography Analysis
3
Equiaxed dimples
- Ductile fracture -
Steel particles
200 µm
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Fractography Analysis
2
Equiaxed dimples
- Ductile fracture -
Steel particles
50 µm 1 mm
MECHANICAL PROPERTIES
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG
Conclusions
9 The welding parameters chosen ensure high quality joints since:
- High surface quality
- Absence of macro cracks after welding process
9 The FSW process cause:
- Recovery/recrystallization in the stir-welded zone
- Significant strengthening of the stir-welded zone due to
formation of fine-grained microstructures in steel
- Presence of the brittle intermetallic Fe2Al5 phase at the
Al-Fe interface
9 The welding characterization proves:
- The intermetallics are responsible for failure in tensile
deformation
- Ultimate tensile strength equal to 75% with respect to
the base material AA6181-T4
MAX-PLANCK-INSTITUT
FÜR EISENFORSCHUNG

Download Report