Correlation of Tensile Properties and Fracture Toughness with Microstructural Features for Al-Li 8090 Alloy Processed by Cryorolling and Post-rolled Annealing

The influence of cryorolling and post-deformation annealing on the tensile and fracture behaviour of aluminium-lithium (Al 8090) alloy is reported in the present investigation. The solution-treated (ST) alloy was cryorolled (CR) up to the true strain of 2.3 to achieve ultrafine-grained (UFG) microstructure and then annealed at different temperature ranging from 100 to 350 degrees C. CR samples showed a significant increase in tensile strength (similar to 373 MPa), hardness (similar to 120 HV), and fracture toughness [K-Q (21.9 MPa root m), K-ee [27.9 MPa root m), J integral (21.8 kJ/m(2))], while huge drop in ductility of CR alloy is observed as compared to coarser grain ST alloy. After annealing in the temperature ranging from 100 to 350 degrees C, the significant changes in the tensile and fracture behaviour of bulk UFG Al 8090 alloy were noticed. The tensile strength and fracture toughness were gradually improved up to the temperature 150 degrees C and observed to be maximum (similar to 561 MPa) at 150 degrees C, while beyond this temperature, a significant drop in these properties was observed. The improved tensile and fracture properties of cryorolled followed by annealed alloy at 150 degrees C could be attributed to the precipitation of S' (Al2CuMg) and delta (Al3Li) phase as observed from XRD and TEM studies.