Superplastic behavior of an Al–Mg–Li alloy

A novel thermomechanical processing has been developed for producing fine-grained Al–Mg–Li alloy 1420 sheet for superplasticity. The refined microstructure had layers of different grain structure through the normal direction of the sheet. The surface layer (SL) had fine, nearly equiaxed grains whereas the center layer (CL) had coarse, elongated grains. The superplastic properties and microstructural evolution of alloy 1420 with such microstructure were investigated using uniaxial tensile tests. It was shown that the refined alloy exhibited considerable elongations of 580–915% when deformed at 510–540 °C and initial strain rates from 5 × 10−4 to 1 × 10−3 s−1. Microstructure observation revealed that the alloy 1420 exhibited unusual cavitation behavior and extensive GBS occurred when tested at 510 °C and above, however, the occurrence of GBS was not uniform. The effects of temperature and strain on grain size and shape, cavity size and volume fraction in the SL and CL were determined, respectively.