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 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

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

Processing of large coils AA pure aluminium 99.9% MaterialMgMnFeSiCuTiCrAl AA Balance

Experimental methods Knoop microhardness KHN = F/A = 10*F/CL 2 Where: F = applied load in N A = the unrecovered projected area of the indentation in mm 2 L = measured length of long diagonal of indentation in mm C = = Constant of indenter relating projected area of the indentation to the square of the length of the long diagonal.

0.15mm 0.3mm 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 R, resistance in Ω, f, form factor in m, L, the length of the specimen in m, S, the section in m 2 Relative resistivity changes

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

Initial microstructure after ARB processing

TEM

Coarse particles rich in Fe, Mn, Si

Resistivity measurements

Knoop microhardness

Average Knoop microhardness

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