Influence of twist extrusion process on consolidation of pure aluminum powder in tubes by equal channel angular pressing and torsion

In comparison with the conventional equal channel angular pressing (ECAP) process, a comprehensive study of influence of twist extrusion (TE) process on consolidating pure aluminum powder in tubes (PITs) by equal channel angular pressing and torsion (ECAPT) was conducted via three-dimensional (3D) finite element simulation, experimental investigation and theoretical analysis. Simulation results revealed that during the consolidation of aluminum powder particles by ECAPT, TE process played a significant role of back pressure. Due to the torsional shear and high hydrostatic pressure exerted by twist channel, both the magnitude and homogeneity of the effective strain were increased markedly. After one pass of ECAPT process using a square channel with an inner angle of 90° and a twist slope angle of 36.5° at 200 °C, commercial pure aluminum powder particles were successfully consolidated to nearly full density. Simulation and experimental results showed good agreement. In the microstructure observations, grains were greatly refined. At the same time, porosities were effectively eliminated by shrinking in size and breaking into small ones. Microhardness test indicated that strain distribution of ECAPT-processed billet was more homogeneous with respect to the ECAP-processed one. All these improvements may be attributed to the extreme intense shear strain induced during ECAPT and the increase in self-diffusion coefficient of aluminum due to the back pressure exerted by TE process.