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