Nano-indentation behavior of layered ultra-fine grained AA8006 aluminum alloy and AA8006-B4C nanostructured nanocomposite produced by accumulative fold forging process

Abstract

In this article, a new severe plastic deformation (SPD) process called accumulative fold-forging (AFF) was implemented to produce layered ultra-fine grained (UFG) AA8006 aluminum alloy and AA8006-B4C (35 nm, 10 vol%) nanostructured (NS) nanocomposite materials. The basis of this novel SPD process involves repetitive folding and forging steps with or without the incorporation of large fractions of nanoparticles between aluminum foil layers; this results in a uniform dispersion of the nanoparticles with less clustering/aggregation, low fraction of porosity, and strong bonding between the layers. Cyclic fold-forging process leads to refining the grain structure of aluminum matrix down to UFG range of ~200 nm and nano-sized range of ~35 nm with and without the B4C nanoparticles. In the present paper, mechanical property and strengthening mechanisms of the produced materials and the contributions of precipitates, nano-layers, nano-grains, and nanoparticles were assessed using a localized nano-indentation testing technique at ambient temperature along different directions. By introducing nano-sized B4C particles between the nano-layers, the modulus and hardness improved up to two times with the average values of ~67.4 and 2.15 GPa, respectively compared to the AFF processed alloy.