Abstract
2 mm thick pure aluminium sheets (99.99 % Al) were processed by accumulative rollbonding (ARB) at room temperature (RT) and under cryogenic conditions (CC, -196 degrees C). Their microstructure was characterized by means of electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), mechanical properties were examined by hardness measurements.
Nearly equiaxed subgrains with a relatively high dislocation density in their interior were observed after the 1st ARB cycle. The following cycles result in subgrain flattening and reduction of inner dislocation density by recovery.
The distribution of misorientations of the grain boundaries in CC and RT samples does not differ significantly; only the CC sample has a little higher fraction of the low-angle grain boundaries (LAGB) with misorientation 2 degrees -5 degrees at the expense of LAGB (5 degrees -15 degrees). The hardness increases vitally only during the first ARB cycle at RT; a slight decrease is even observed starting from the 2nd ARB cycle.
During processing at CC, this decrease is shifted to the 4th cycle due to reduced post-dynamic recovery at low temperatures.