Complex study of multilayer Al99.99/AlMg3 laminates prepared by accumulative roll bonding

1. Complex study of multilayer Al99.99/AlMg3 laminates prepared by accumulative roll bonding Miroslav Cieslar Charles University in Prague, Faculty of Mathematics and Physics, Department of Physics of Materials, KeKarlovu 5, CZ-121 16 Prague 2, Czech Republic

2. Outline Introduction Material ARB processing Experimental methods Microstructure Mechanical properties Electrical resistivity Microstructure evolution In-situ observations Summary

3. 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

4. Material Twin-roll cast AA5754 and AA1199 Direct-Chill Casting tandem hot-rolling scalping & homogenization annealing 7 - 9 mm 600 mm ingot cold-rolling break-down mill Twin-Roll Casting The technology based on TRC is much shorter, i.e., energy and cost effective. annealing t = 5 - 9 mm 0.1 -0.006mm cold-rolling

5. Processing of large coils AA 1199 - pure aluminium 99.9%

6. Experimental methods Knoop microhardness KHN = F/A = 10*F/CL2 Where:F = applied load in NA = the unrecovered projected area of the indentation in mm2L = 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.

7. 0.15mm 0.3mm procedure of hardness measurements Knoopmicrohardness as a function of distance from the surface of the sample after 3 ARB steps

8. Electrical resistivity () measurements Standard four-point method in liquid nitrogen during isochronal step-by-step annealing with the step 20K/20min R, resistance in Ω, f, form factor in m, L, the length of the specimen in m, S, the section in m2 Relative resistivity changes

9. Microstructure observations The light optical microscope NIKON – EPIPHOT 200 Electron microscope JEOL JEM 2000FX with JEOL single-tilt heating stage

10. Initial microstructure after ARB processing 5 1 3 4 5 2

11. TEM Al Mg Mg 1 Al Mg 2 interface

12. Al Mg Mg 3 Al Mg Mg 4

13. 5 Al Mg Mg Coarse particles rich in Fe, Mn, Si

14. Resistivity measurements

15. Knoop microhardness

16. Average Knoop microhardness

17. Only moderate changes of resistivity below 350 °C followed by significant resistivity increase Fast drop of microhardness only between 120 and 350 °C