Particle dispersion and grain refinement of in-situ TiB2 particle reinforced 7075 Al composite processed by elliptical cross-section torsion extrusion

A modified torsion extrusion (TE) method, entitled elliptical cross-section TE (E-TE), was proposed as a severe plastic deformation (SPD) process to refine the microstructures and improve the mechanical properties of a bulk in-situ TiB2 particle reinforced 7075 Al composite. The material is deformed in a rotatable cavity with variable cross-section that varies from circular to elliptical then to circular, by which a severe shear effect is subjected to the material. Numerical simulations show that the E-TE processed sample underwent larger shear deformation than the ones processed by the conventional TE and the forward extrusion. Microstructure characterizations demonstrate that the E-TE processed sample results in better microstructures with uniformly distributed particles and fine equiaxed recrystallized grains due to the larger deformation. Mechanical tests on the processed samples demonstrate that the E-TE processed sample has the best combination of strength and ductility. Besides, with the aid of the torsion effect, the E-TE operation requires the minimum extrusion load to achieve the same extrusion ratio. The proposed E-TE process thus can be used as an efficient process for optimizing mechanical properties of metal matrix composites.