Transition in deformation mechanism during high-temperature tensile testing of friction-stir-processed 5083 aluminum alloy

The stress–strain relationship and microstructural evolution of a fine-grained 5083 aluminum alloy produced via friction-stir processing (FSP) during high-temperature tensile deformation were investigated. The FSP of the 5083 aluminum alloy resulted in the formation of a homogeneous fine-grained microstructure. Based on the stress–strain relationship, it was found that the 5083 aluminum alloy exhibited a large elongation, especially at a temperature above 693 K. The stress exponent and the activation energy for deformation, which were determined by the flow stress at a nominal strain of 0.03, were approximately 2.5 and 123 kJ/mol, respectively. These results suggest that grain boundary sliding accommodated by the solute drag motion of dislocations was the rate-controlling process in the early stages of deformation. The largest elongation of 350% occurred at 743 K and an initial strain rate of 1.0 10⁻³ s⁻¹. In this case, the grain aspect ratio increased with increasing nominal strain, which indicated that equiaxed grains continuously elongated along the tensile axis during high-temperature deformation because of dislocation creep. The value of the stress exponent increased with increasing strain. From our experimental results, the dominant deformation mechanism was determined to change during the tensile test, and the contribution of dislocation creep to the high-temperature deformation increased as the deformation proceeded.