Improvement of fracture toughness of ultra fine grained Al-Li 8090 alloy processed through multi axial forging

In the present work, mechanical properties, microstructural characteristics and fracture behavior of severely deformed Al-Li 8090 alloy processed through multi axial cryo forging has been investigated and compared with the room temperature forged conditions. Enhancement in the mechanical properties, LEFM fracture toughness and EPFM toughness parameter (J-integral) of severely deformed Al-Li 8090 alloy with a cumulative true strain of 1.2, 2.4 and 3.6 is observed at Cryo forged (CF) condition as compared to room temperature forged (RTF) conditions due to the accumulation of higher dislocation density, dislocation substructure and formation of UFG microstructure. Effective retardation of dynamic recovery and climb at liquid nitrogen temperature (LNT, -196 °C) is responsible for higher dislocation accumulation in CF sample compared to the samples subjected to room temperature forging. The improved fracture toughness of CF samples is attributed to the delay in crack initiation as well as crack propagation phase resulting from Hall-Petch strengthening, grain boundary strengthening, and dislocation strengthening.