Effects of solution-aging treatment on the strength-ductility synergetic improvement of electron beam freeform fabricated TiB₂/Al-Zn-Mg-Cu composites

The effects of solution-aging treatment on the microstructure and mechanical properties of TiB₂/Al-Zn-Mg-Cu composites prepared by electron beam freeform fabrication were investigated. Both the as-deposited and heat-treated composites exhibited a typical equiaxed grain structure. The average grain size of the as-deposited specimen was 16.0 µm. With the aging time extended, the average grain size increased to 26.4 µm in the 125℃/36 h specimen. TiB₂ particles could impede grain boundary migration, thus effectively suppressing grain growth through the Zener pinning mechanism. During the solution-aging process, lath-shaped S-Al₂CuMg phase precipitated within the grains, which effectively hindered dislocation motion. η-MgZn₂ phase was predominantly located at the grain boundaries. TiB₂ particles promoted a uniform distribution of precipitates as heterogeneous nucleation sites during aging process. The tensile strength of the specimens increased from 308 MPa to 372 MPa in horizontal direction, and the elongation of the composites increased significantly, from 9.3% to 15.7%. The synergistic effect of nano-TiB₂ particles and high-density precipitates enhanced the work hardening rate and optimized the strength-ductility synergy, which was attributed to the uniform distribution of precipitates, load-transfer strengthening and Orowan strengthening of the TiB₂ particles. This research was expected to provide theoretical and technical support for the development of lightweight aerospace structural components.