Microstructure and tensile properties of Al–Mn alloy processed by accumulative roll bonding

Microstructure and tensile properties of ultrafine grained Al–Mn alloy by ARB at room temperature were investigated. With the cycles of ARB, the average grain size becomes smaller, and the pancake shaped ultrafine grains develop to be about 250 nm after five cycles. Meanwhile, the MnAl 6 phase in the shape of spherical particle is refined and uniformly distribute in the matrix. A fairly uniform microstructure would be facilitated by a multi-parabolic profile of shear strain distribution across the thickness of sheet. In the present ARB process, there exist two types of changes in deformation mode. One is changed from shear deformation (in the surface regions) to plain strain rolling (in the center). The other is that strain path is reversible due to a change of rolling direction in alternate cycles. Therefore, the process of grain refinement can be accelerated than the conventional ARB. The tensile tests show Al–Mn alloy exhibits strain hardening behavior after yielding without a sudden fracture even up to five cycles of ARB. The more the cycles of ARB, the smaller the decrease of work-hardening rate of Al–Mn specimens. The enhanced ductility was explained by dynamic recovery, the formation of ultrafine MnAl 6 phase, work-hardening and strain rate sensitivity.