Annealing Effects on Accumulative Roll Bonded Aluminium Laminates of Different Purities

Sharma, B (2013) Annealing Effects on Accumulative Roll Bonded Aluminium Laminates of Different Purities. Masters thesis, Indian Institute of Technology Hyderabad.

Preview

Text
MS11M1001.pdf - Submitted Version
Download (9MB)

Abstract

Accumulative roll-bonding (ARB) is a severe plastic deformation technique which is used for ultrafine grains development in bulk laminates. Composite laminates of dissimilar materials can also be bonded through ARB. In the present work different purity aluminium laminates are roll bonded and annealed at different temperatures to study their static recrystallization behavior. Aluminium laminates of commercial pure 99.5 weight % (henceforth will be called as “A”) and ultra-high pure 99.999 weight % (will be called as “C”) after annealed at 500oC for 1 hour and roll bonded up to 10 rolling cycles, are asreceived. These are heat treated for 30 mins in salt bath furnace from 150oC to 450oC with 25oC temperature intervals followed by water quenching and its further hardness, microstructural characterization and crystallographic texture studies are carried out on them. Vickers Micro-Hardness studies explained hardness profiles with different number of rolling cycles and annealing temperatures. Simultaneous studies using scanning electron microscopy (SEM)-electron backscattered diffraction (EBSD) mappings, their recovery, recrystallization and grain growth phenomena could be analyzed. For as-received roll bonded samples, it is observed that with increasing number of rolling cycles hardness decreased (dynamic recovery and recrystallization) and then increased (deformation of the recrystallized grains) during ARB processing itself. But for the heat treated samples at all the temperatures, hardness values for each rolled cycles is decreased from their roll bonded values (due to recovery, static recrystallization and grain coarsening). The SEM-EBSD maps of rolled ARB specimens showed discontinuous dynamic recrystallization in ultrahigh pure aluminium (C) layer and dynamic continuous recovery/recrystallization in commercially pure aluminium (A) layer, which ultimately developed into ultrafine grained microstructure by 10 cycles of ARB. Static recrystallization and grain coarsening is noticed through SEM-EBSD mapping after heat treatment of these ARB specimens, which first changed the ultrafine grained ARB microstructure into coarse long cellular-type microstructure and then coarsened into large equiaxed microstructure. The SEM-EBSD orientation maps also provided their crystallographic texture evolution details with each cycles and its heat treatments. In ARB specimens (AC-1 to AC-10) Cube and shear Cube texture components are majorly noted in C layer with Copper, S, Shear Copper and Shear S are found in A layer. The shear components might be generated from the friction between the rolls and the specimen surface. Whereas, annealing of all the ARB specimens mostly produced coarse grain Cube texture mainly through static recrystallization and grain coarsening.

[error in script]

IITH Creators: