Deformation behavior and microstructure evolutions in Ti-6Al-4V extrusion

Abstract

The metal-forming behavior and microstructure evolution in Ti-6Al-4V during backward extrusion for tube making are investigated. 2-D FE simulation was used. Dynamic materials model (DMM) including instability criterion and the modified Cockcroft-Latham criterion were employed to predict the forming defects and to predict the crack formation inside or outside the extruded tube. The soundness and microstructure of the backward-extruded tubes are affected by process parameters, such as billet temperature, extrusion speed, die geometry and temperature, lubrication and heat transfer conditions. Local microstructures in the deformed tubes were simulated based on the specimen-base compression tests in relation to the process parameters. The simulation results for the backward extrusion were compared with the experimental observations. The die chilling and deformation heating showed a great influence on the deformation mode and the evolution of microstructures. The changes and non-uniformities in the microstructure of extruded tubes were attributed to non-uniform distribution of strain and temperatures in the extruded tubes for the given test conditions.