Production of nano-grained structure in 6061 aluminum alloy strip by accumulative roll bonding

Accumulative roll-bonding (ARB) process is a severe plastic deformation (SPD) process capable of developing grains below 1 μm in diameter. In this study, the ARB process was applied on 6061 aluminum alloy up to 5 cycles at ambient temperature without any lubrication. Microstructural characterizations were performed by transmission electron microscopy (TEM). The dislocation density changes during deformation were calculated using a recently developed JAVA based software, Materials Analysis Using Diffraction (MAUD), based on Rietveld's whole X-ray pattern fitting methodology. It was found that the presence of Mg in solid solution efficiently promoted and increased the dislocation density in the alloy during ARB process. This resulted in a continuous recrystallization phenomenon, leading to a microstructure consisting of small recrystallized grains with an average diameter of about 100 nm. The tensile tests were conducted on the ARBed strips. The tensile strength increased 2.5 times more than the initial value. However, the elongation dropped abruptly at the first cycle, and then decreased slightly.

► Formation of small recrystallized grains with average grain sizes of 100 nm in the microstructure after 5 ARB cycles.
► Continuous recrystallization phenomenon was a responsible mechanism for the formation of small grains during the ARB process.
► When the number of ARB cycles was raised, the tensile strength value improved while the elongation dropped abruptly.