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The superplastic (SP) properties of a modified 5083 alloy (Al-4.7Mg-1.6Mn) were evaluated by tensile tests and microstructural characterization over a range of strain rates from 0.0005 to 0.1 s Ϫ1 , temperatures from 500 ЊC to 550 ЊC, and initial grain sizes from 8.7 to 17 m. The fine-grained material was found to exhibit strain-rate sensitivity values of greater than 0.5 over the strain-rate range of 0.002 to 0.1 s Ϫ1 , while the coarser-grained material appeared to deform as a Class I solid solution by glide-controlled dislocation creep. It was found that the mechanical properties could be adequately represented by a semiempirical constitutive equation which reflected the flow hardening due to dynamic grain growth, the change in m with strain and strain rate, and the transition between SP deformation and dislocation creep with strain rate. Microstructural examination revealed the presence of several pre-existing cavities associated with intermetallic particles. Tensile elongations of up to 525 pct were obtained at a strain rate of 10 Ϫ3 s Ϫ1 .

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