Microstructure characterization and solid welding mechanism of TiB2/6061Al composite profile fabricated by porthole die extrusion

Abstract

The TiB2/6061Al composite profile with sound welding quality and good mechanical properties was fabricated by porthole die extrusion. The effects of TiB2 particles on the microstructure evolution and mechanical properties were investigated, and the welding mechanism was clarified. The results indicated that the weld seam in both 6061Al and TiB2/6061Al profiles disappeared as porthole die extrusion progressed. TiB2 particles refined the grain structure by promoting the occurrence of dynamic recrystallization through particle stimulated mechanism (PSN-DRX) and inhibiting the grain growth. The interface between TiB2 particles and 6061Al matrix was in good bonding status and modified by MgAl2O4 phase. The welding mechanism in the area far away from TiB2 particle is mainly the nucleation and growth of discontinuous dynamic recrystallization (DDRX) initiated by the bulging mechanism. In the vicinity of TiB2 particle, the nucleation of DDRX is suppressed due to the formation of particle deformation zone containing high-density dislocations, and the nucleation and growth of PSN-DRXed grains become the dominated welding mechanism. The strong β-fiber texture and relatively weak α-fiber texture were observed in both 6061Al and TiB2/6061Al profiles, while the addition of TiB2 particles greatly reduced the intensity of main textures, which in turn weakened the differences in tensile strength at different locations. TiB2 particles also contribute to better mechanical performances due to the effects of grain refining, load transfer and dislocation strengthening.