Strain rate dependence of properties of cryomilled bimodal 5083 Al alloys

The strain-rate-dependent deformation behavior of bimodal 5083 Al alloys processed by cryomilling is studied in the present investigation. The alloys were processed by hot extrusion of a mixture of cryomilled and unmilled Al powders. Their tensile stress-strain curves displayed a short work-hardening region, followed by a small stress drop after the ultimate stress while their tensile ductility increased with decreasing strain rates. Compressive stress-strain curves displayed a nearly perfect plastic behavior and negative strain rate sensitivity. Inspection of the deformation characteristics and fractography revealed that the higher ductility at lower strain rate was caused by effective diffusion-mediated stress relaxation, which delayed microcrack nucleation and propagation. Furthermore, crack blunting/bridging by ductile coarse grains played a significant role at lower strain rates. The phenomenon of the negative strain rate sensitivity of compression flow stress is proposed to be as a consequence of dynamic strain aging. © 2006 Acta Materialia Inc.