Structural features of ultrafine-grained aluminum processed through accumulative roll bonding providing improved mechanical properties and thermal stability

Using transmission electron microscopy, tension and indentation tests we studied commercially pure aluminum processed by severe plastic deformation through accumulative roll bonding (ARB Al) and equal-channel angular pressing (ECAP Al) up to 8.0 von Mises equivalent strain to find the structural features providing improved mechanical properties and their enhanced thermal stability in the former case. It is revealed that the average size of the elements of the grain-subgrain structure is 23% lower and the strength properties are 19 - 27% higher in ARB Al with respect to ECAP Al. The physical reason for more refinement of the grain-subgrain structure and enhanced mechanical properties is the presence of dispersed alumina nanoparticles introduced into the bulk of ARB aluminum from the surface of the bonded stripes during ARB. The thermal stability of microhardness of ARB Al exceeds the respective value of ECAP Al in the temperature interval of 473 - 513 K, where the recrystallization starts to occur. The improved thermal stability of ARB Al is related to the higher resistance to recrystallization due to the presence of alumina nanoparticles on grain boundaries formed during ARB and precipitation of Si from the solid solution on these nanoparticles.