Annealing Effects in Twin-Roll Cast AA8006 Aluminium Sheets Processed by Accumulative Roll-Bonding

Miroslav Cieslar,Michaela Poková

doi:10.3390/ma7128058

Abstract

Ultrafine grained sheets were prepared from a twin-roll cast AA8006 aluminium alloy using accumulative roll-bonding process at room temperature. The evolution of microstructure of sheets after three accumulative roll-bonding passes during isochronal annealing with a constant step of 20 °C/20 min was studied by light and electron microscopy. The influence of the resulting microstructure on mechanical properties was monitored by microhardness measurements. The microhardness increases when the material is annealed up to 160 °C. Above this temperature a fast drop of microhardness occurs followed by a negligible variation at annealing temperatures exceeding 300 °C. In order to map continuously the microstructure changes during annealing, the in situ TEM experiments in the heating stage were performed as a supplement to post-mortem TEM observations.

Highlights

Mechanical properties of metallic materials are very sensitive to the grain size and its reduction increases the yield stress and the tensile strength according to the Hall-Petch relationship [1,2]
Its homogeneity and final thermal stability in aluminium alloys depends on the processing temperature, number of Accumulative roll-bonding (ARB) cycles and on the grain size of the initial material and the size and distribution of coarse primary particles which are generally present in the ingot cast and cold-rolled sheets
The thermal stability and homogeneity is improved in materials with finer particles and small grain size which is typical for continuously twin-roll cast (TRC) aluminium alloys [12,13,14,15,16]

Summary

Introduction

Mechanical properties of metallic materials are very sensitive to the grain size and its reduction increases the yield stress and the tensile strength according to the Hall-Petch relationship [1,2]. The basic principle of the SPD process consists in inducing an extremely high plastic strain into the material resulting in a substantial grain refinement and improved strengths. Its homogeneity and final thermal stability in aluminium alloys depends on the processing temperature, number of ARB cycles and on the grain size of the initial material and the size and distribution of coarse primary particles which are generally present in the ingot cast and cold-rolled sheets. The thermal stability and homogeneity is improved in materials with finer particles and small grain size which is typical for continuously twin-roll cast (TRC) aluminium alloys [12,13,14,15,16]. Because the use of TRC aluminium materials in the industry is continuously more and more frequent the feasibility conditions of ARB processing and thermo-mechanical post-processing become an important part of the SPD materials investigation

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