Effect of Room Temperature Rolling Followed by Annealing on Tensile and Fracture Behaviour of Bulk Ultrafine-Grained Al–Li 8090 Alloy

Abstract

The mechanical properties and microstructural evolution of aluminium–lithium (Al–Li) 8090 alloy subjected to room temperature rolling (RTR) followed by annealing were investigated in the present work. Tensile, hardness test and three-point bend tests were performed to identify the mechanical properties, while optical microscopy, scanning electron microscopy and transmission electron microscopy were used for correlating mechanical properties with microstructural features. Results showed that the tensile strength and hardness increase firstly and then decrease with elevating annealing temperature when the holding time is kept for 1 h that is attributed to the strengthening of grain boundary, solid solution strengthening and precipitation strengthening. An increment in ultimate tensile strength from 265 to 359 MPa (approx. 35% increase) and yield strength from 186 to 234 MPa (approx. 25% increase) was observed substantiating the formation of ultrafine-grained microstructure at room temperature. On annealing in the 100–350 °C temperature range with 50 °C interval, the mechanical properties such as tensile strength and yield strength increase significantly up to 150 °C (UTS-522 MPa and YS-398 MPa); however, there is gradual decrease in the tensile and yield strength observed beyond these temperatures and these values (UTS-124 MPa and YS-109 MPa) become least on annealing at 350 °C. It is observed that a 19% increase in the apparent fracture toughness (K_Q) occurred for RTR Al–Li (8090) alloy as compared to solution-treated Al–Li 8090 alloy in three-point bend test.