Effect of microstructure refinement on high strain rate superplasticity ina PM 2024Al-Fe-Ni alloy

Improvement of high strain rate superplasticity (HSRS) of a high strength P M 2024Al-3Fe-5Ni alloy has been examined in relation to the microstructure refining through a modification of heating condition to testing temperature s. The alloy was fabricated by an air atomization technique, followed by ex trusion at 623 K and warm rolling at 523 K. After the warm rolling, the all oy exhibited ultra fine-grained structure stabilized with a fine dispersion of intermetallic particles. The high strain rate superplastic properties f or the present alloy were remarkably improved by the microstructural refine ment, even at the optimum superplastic temperature of 773 K, which is close to the solidus temperature of about 780 K for the alloy. The finer the siz es of matrix grains and intermetallic particles, the higher values of total elongation and strain rate sensitivity were obtained at a high strain rate range of 10(-1)-10 s(-1) and at a wide temperature range of 713-773 K. The stress concentration during sliding at the particle/matrix interface was c onsidered to be diffusionally relaxed, because the particles were sufficien tly small. A constitutive equation has been obtained through an analysis of high strain rate superplasticity data on the alloy. The high strain rate s uperplastic mechanism for the alloy is probably lattice diffusion controlle d grain boundary sliding.