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Strain Rate Sensitivity Studies of Cryomilled Al Alloy Performed by Nanoindentation

Al 5083 alloy powder was mechanically milled in liquid nitrogen to achieve a nanocrystalline (NC) structure having an average grain size of 50 nm with high thermal stability, and then consolidated by quasi-isostatic (QI) forging. The consolidation resulted in ultrafine grains (UFG) of about 250 nm, and the bulk material exhibited enhanced strength compared to conventionally processed Al 5083. The hardness of as-cryomilled powder and the UFG material was measured by nanoindentation using loading rates in the range of 50−50,000 /N/s, and results were compared with the conventional grain size alloy. Negative strain rate sensitivity was observed in the cryomilled NC powder and the forged UFG plate, while the conventional alloy was relatively strain rate insensitive.