Evaluation of microstructure and superplasticity in friction stir processed 5083 Al alloy

Friction stir processing (FSP) has been developed as a potential grain refinement technique. In the current study, a commercial 5083 Al alloy was friction stir processed with three combinations of FSP parameters. Fine-grained microstructures with average grain sizes of 3.5-8.5 pm were obtained. Tensile tests revealed that the maximum ductility of 590% was achieved at a strain rate of 3 x 10(-3) s(-1) and 530 degreesC in the 6.5-mum grain size FSP material, whereas for the material with 8.5-mum grain size, maximum ductility of 575% was achieved at a strain rate of 3 x 10(-4) s(-1) and 490 degreesC. The deformation mechanisms for both the materials were grain boundary sliding (m similar to0.5). However, the 3.5-mum grain size material showed maximum ductility of 315% at 10(-2) s(-1) and 430 degreesC. The flow mechanism was solute-drag dislocation glide (m similar to0.33). This study indicated that establishing a processing window is crucial for obtaining optimized microstructure for optimum superplasticity.