PROCESSING ROUTES FOR INTER-TRANSFORMATION BETWEEN LOW- AND HIGH-TEMPERATURE 8090 Al-Li SUPERPLASTIC SHEETS

The current paper reports a series of processing routes for fabrication and inter-transformation of the low-temperature and high-temperature superplastic 8090 Al-Li sheets. There required one preloading procedure for one to transfer the low-temperature superplastic sheet into a high-temperature one, which might satisfy the needs of various industry applications. The TMT process included hot rolling, solution treatment, prolonged overaging, warm or cold rolling, and final heating and loading to desired properties. The resulting LTSP and HTSP thin sheets exhibited good superplastic elongations at either low (350 °C) or high (525 °C) temperatures, respectively, with or without adding back pressure. Warm rolling yielded slightly higher elongations, but such a minor degradation when using cold rolling may be acceptable for practical applications. The m-values over strain rates of 2-8x10^-4 s^-1 were within 0.28-0.35 for the self-processed LTSP sheets when loaded at 350 °C and 0.45-0.50 for the self-processed HTSP materials when tested at 525 °C. The final (sub)grain size, after 400-700% elongation was around 3.0-4.0 μm in the LTSP materials and 10-15 μm in the HTSP sheets.