A STUDY OF SUPERPLASTICITY IN A MODIFIED 5083-AL-MG-MN ALLOY

The superplastic (SP) properties of a modified 5083 alloy (Al-Mg-4.7-M n-1.6) were evaluated by tensile tests and microstructural characteriz ation over a range of strain rates from 0.0005 to 0.1 s(-1), temperatu res from 500 degrees C to 550 degrees C, and initial grain sizes from 8.7 to 17 mu 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(-1), while the coarser-grained material appeared to deform as a Class I solid solution by glide-controlled dislocation cr eep. It was found that the mechanical properties could be adequately r epresented by a semiempirical constitutive equation which reflected th e flow hardening due to dynamic grain growth, the change in m with str ain and strain rate, and the transition between SP deformation and dis location creep with strain rate. Microstructural examination revealed the presence of several pre-existing cavities associated with intermet allic particles. Tensile elongations of up to 525 pet were obtained at a strain rate of 10(-3) s(-1).