Evaluating the high temperature superplastic behavior of a thermomechanically processed Al–Cu aluminum alloy through miniaturized testing method

The high temperature superplastic behavior of ultrafine grain A206 aluminum alloy was examined employing miniaturized shear punch jump test method. To achieve a fine-grained microstructure, accumulative back extrusion were applied at 200 °C up to 1, 3 and 5 passes on the as-annealed microstructure. The high temperature mechanical properties of the products were assesses at 100, 200 and 300 °C. The strain rate sensitivity indices (m) of the processed specimens were evaluated under the base strain rate of 0.004 s⁻¹ with the incremental jump to 0.01s⁻¹, and various temperatures. The temperature of 300 °C was found as the optimum temperature for superplastic deformation of the experimented material, and a considerable increase in the m value was observed after 3 and 5 passes. The highest elongation to fracture value was observed in 5-passes processed specimen at 300 °C where the m value was obtained about 0.35. In this condition, grain boundary sliding was announced to be the dominant deformation mechanism. Lastly, TEM and XRD characterization exposed that the fine Al₂Cu precipitates are rarely observed in 1-pass processed microstructure while a high fraction of fine precipitates (7–10 nm) were found in 5-passes processed material. These fine precipitates were thermally stable and coherent with the aluminum matrix, and thus were able to pin the grain boundaries and at the high temperatures and decrease grain growth rate. (paper)