Development of superplasticity in 8090 Al-Li alloy by static recrystallization

Investigations have been conducted to develop a thermomechanical processing (TMP) route for 8090 Al--Li alloy by static recrystallization. The superplastic behavior developed in an 8090 alloy using this new method is compared with that of commercially available superplastic forming sheet. The 8090 Al--Li plates of 35 mm thickness and superplastic sheets for 2 mm thickness were commercially manufactured. To obtain a fine grained microstructure from the standard plate, three TMP routes were used. The plate was processed to a sheet of 1.5 mm thickness through these TMP routes. It was found that applying cold deformation before an aging process could substantially improve the superplastic behavior of the material processed by a static recrystallization route. Although the statically recrystallized sheet had a much coarser initial grain, the level of superplasticity was similar to that of the dynamically recrystallized fine grained 8090 SPF sheet. More resistance to grain growth at low superplastic elongations is believed to exist in the statically recrystallized material.