Strength and ductility improvement of an in-situ TiB2/Al–Zn–Mg–Cu composite by elliptical cross-section torsion extrusion

Abstract

In this study, a novel severe plastic deformation method, i.e., elliptical cross-section torsion extrusion (E-TE), was applied to improve the performance of an in-situ TiB2/Al–Zn–Mg–Cu composite to promote the application of the composite in the aerospace industry. Results evidence that the E-TE can homogenize the particle distribution and refine the composite's microstructure in a one-step process, thus yields a simultaneous improvement of the strength and ductility. Based on the experimental and simulation results, the underlying microstructure evolution during the E-TE process is revealed that the E-TE imposes large shear deformation on the composite, which mechanically fragments large grains and smashes particle bands/clusters; meanwhile, the dispersed reinforced particles and precipitations facilitate grain refinement via both accelerating continuous dynamic recrystallization and particle stimulated nucleation, and impede grain growth by hindering grain boundary migrant. Therefore, the E-TE processed composite exhibits optimized microstructures of uniformly distributed particles and fine-equiaxial grains; and its strength is increased via the grain boundary strengthening, while the ductility is improved due to the damage-generation retardation and crack-propagation impediment resulted from the fine-homogeneous microstructures. However, the precipitation dissolution under high temperatures weakens the particle/matrix interface bonding and results in void formation, leading to less mechanical properties improvement.