Effect of grain refinement on mechanical properties of ball-milled bulk aluminum

In this study, high quality bulk ultra-fine grained and nanocrystalline pure aluminum samples were prepared through room temperature ball milling, cold and warm compaction, sintering, and annealing processes. The as-received (−325 mesh) powder was subjected to different milling times in order to achieve specimens with different average grain sizes (d). The prepared samples were then subjected to uniaxial compressive loading to large strains (∼45%) to investigate the effect of grain size on the stress–strain response of the material. The 10-h milled bulk nanocrystalline samples (d = 82 nm) were tested at a very wide range of strain rates from quasi-static to dynamic regimes. The strain rate sensitivity of the material increased as the grain size was reduced to nanometer realm; the flow stress, and work hardening behavior were dramatically influenced by change in the grain size (milling time).