Influence of strain rate on the mechanical properties in fine-grained aluminum alloys

Abstract

Fine-grained IN905XL aluminum alloys with five grain sizes between 0.8 and 8.1 μm have been developed by a combination of mechanical alloying and conventional extrusion in order to investigate the influence of the strain rate on the mechanical properties. Negative strain rate sensitivity of flow stress is observed up to 10 s −1 for all samples. Above the strain rate of 1 × 10 3 s −1, however, all samples show the positive strain rate sensitivity of strength. Total elongation at high strain rates is generally larger than that at low strain rates. Flow stresses increase with decreasing grain size for all strain rates. The measured values of strength of the coarse grained IN905XL with sizes above 4.3 μm agree with the values estimated from a cooperation of the strengthening by the grain size refinement, magnesium solute atoms and oxides and carbides dispersion. In the Hall-Petch relations at high strain rates, the gradient of the curve increases with increasing reciprocal square root of the grain size. For fine-grained samples, therefore, an additional strengthening mechanism should be considered such as the difference in the characteristics of the boundary.