Evolution of texture, micro structure and mechanical property anisotropy in an Al-Li-Cu alloy

The evolution of hot deformation texture, microstructure and yield strength anisotropy in an Al-Li-Cu alloy AF/C489 was studied in the as-extruded, solution heat treated and peak-aged condition. Cast AF/C489 alloy with a random texture was extruded at six temperatures ranging from 260 to 538°C and immediately quenched to capture texture and microstructure at the extrusion temperature. In the as-extruded condition, significant amounts of the major rolling texture components, namely, Br 112〈110〉, S 123〈634〉 and Cu 112〈111〉 were observed at all extrusion temperatures. However, at extrusion temperatures above 480°C there was a sharp rise in the intensity of Br component. When the extruded alloy was solution treated the Br intensity remained stable for the two highest extrusion temperatures. However, solution heat treatment (SHT) following extrusion at lower temperatures resulted in the loss of all the rolling texture components including Br. Furthermore, the solution heat treatment following extrusion at temperatures below 330°C showed presence of significant amount of ND rotated cube (100〈130〉). It is suggested that formation of Br texture may be due to the development of shear bands. Increase in dynamic recovery at high extrusion temperature enhances the shear banding tendency and consequently increased presence of Br. This is consistent with negligible recrystallization during solution treatment following elevated temperature extrusion as observed by optical microscopy. Significant recrystallization during SHT following low temperature extrusion results in the presence of rotated cube components. This is consistent with the presence of more particles at low temperature as observed by transmission electron microscopy. The yield stress anisotropy in the SHT material is attributed to crystallographic texture in the SHT material whereas in the extruded case the anisotropy is due to the combined effect of particles and texture.