Complex study of multilayer Al99.99/AlMg3 laminates prepared by
accumulative roll bonding
Charles University in Prague, Faculty of Mathematics and Physics, Department of Physics of Materials, Ke Karlovu 5, CZ-121 16 Prague 2, Czech
Republic
Miroslav Cieslar
Outline• Introduction• Material• ARB processing• Experimental methods• Microstructure• Mechanical properties• Electrical resistivity• Microstructure evolution•In-situ observations• Summary
Introduction• Ultrafine - grained materials (UFG)• Most common methods: ECAP (Equal Channel Angular Extrusion or Pressing ), HPT (High Pressure Torsion )• Since 1998 – ARB (accumulative roll-bonding
Schematic diagrams of (a) ECAP (b) HPT process
Steps during ARB processing
MaterialTwin-roll cast AA5754 and AA1199
4
Twin-Roll Casting
t = 5 - 9 mm 0.1 -0.006mm
Direct-Chill Casting
scalping & homogenization
cold-rollingbreak-down mill
tandem hot-rolling
600 mm ingot
7 - 9 mm
cold-rolling
annealing
annealing
The technology based on TRC is much shorter, i.e., energy and cost effective.
Processing of large coils
AA 1199 - pure aluminium 99.9%Material Mg Mn Fe Si Cu Ti Cr Al
AA 5754 2.69 0.39 0.31 0.20 0.006 0.033 0.002 Balance
Experimental methods
Knoop microhardness
KHN = F/A = 10*F/CL2 Where:F = applied load in NA = the unrecovered projected area of the indentation in mm2
L = measured length of long diagonal of indentation in mmC = 0.07028 = Constant of indenter relating projected area of the indentation to the square of the length of the long diagonal.
0.15mm
0.3mm
40
60
80
100
120
140
160
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Distance (mm)
Kno
op H
ardn
ess
procedure of hardness measurements
Knoop microhardness as a function of distance from the surface of the sample after 3 ARB steps
Electrical resistivity () measurements
Standard four-point method in liquid nitrogen during isochronal step-by-step annealing with the step 20K/20min
),( LSfR
R, resistance in Ω, f, form factor in m,L, the length of the specimen in m,S, the section in m2
0
0)(
AT
Relative resistivity changes
Electron microscope JEOL JEM 2000FXwith JEOL single-tilt heating stage
The light optical microscope NIKON – EPIPHOT 200
Microstructure observations
Initial microstructure after ARB processing
1
2
3
4
5
5
TEM
1
2
Al
Al
Mg
Mg
Mg
interface
3
4
Al
Al
Mg
Mg
Mg
Mg
Coarse particles rich in Fe, Mn, Si
5Al Mg
Mg
Resistivity measurements
Relative resistivity (%)
-10
0
10
20
30
40
50
60
70
80
50 100 150 200 250 300 350 400 450 500
Annealing temperature (°C)
Δρ/
ρ (%
)
ARB1
ARB2
ARB3
ARB4
ARB5
Knoop microhardnessMinimum Knoop microhardness: Al layer
15
20
25
30
35
40
45
50
55
0 50 100 150 200 250 300 350 400 450 500
Annealing temperature (°C)
Kno
op m
icro
hard
ness
ARB1ARB2ARB3
ARB4ARB5
Maximum Knoop microhardness: AlMg3
60
70
80
90
100
110
120
130
140
150
0 50 100 150 200 250 300 350 400 450 500
Annealing temperature (°C)
Kno
op m
icro
hard
ness
ARB1ARB2ARB3ARB4ARB5
Average Knoop microhardness
Mean Knoop microhardness
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350 400 450 500
Annealing Temperature (°C)
Kno
op m
icro
hard
ness
ARB1ARB2ARB3ARB4ARB5
Relative resistivity (%)
-10
0
10
20
30
40
50
60
70
80
50 100 150 200 250 300 350 400 450 500
Annealing temperature (°C)
Δρ/
ρ (%
)
ARB1
ARB2
ARB3
ARB4
ARB5
Mean Knoop microhardness
30
40
50
60
70
80
90
100
0 50 100 150 200 250 300 350 400 450 500
Annealing Temperature (°C)
Kno
op m
icro
hard
ness
ARB1ARB2ARB3ARB4ARB5
Only moderate changes of resistivity below 350 °C followed by significant resistivity increase
Fast drop of microhardness only between 120 and 350 °C