Exploring the potential of FSW-ed Al–Zn–Mg–Cu-based composite reinforced by trace in-situ nanoparticles in manufacturing workpiece with customizable size and high mechanical performances.

Al–Zn–Mg–Cu alloys that are prone to segregation and hot cracks always encounter difficulty in manufacturing large-size workpiece with desirable strength-plasticity synergy, especially when the tonnage of the extruder exceeds 6000 tons. This work puts forward a novel idea to address this challenge by joining extruded profiles of Al–Zn–Mg–Cu-based composite reinforced by trace in-situ TiC–TiB 2 nanoparticles through friction stir welding (FSW). The extruded profiles of Al–Zn–Mg–Cu-based composite along transverse direction (TD) achieved superior yield strength (σ Y) of 827 MPa and large plastic strain (ε p) of 10.2%. The σ Y of FSW-ed joint along TD reached 847 MPa, and the ε p was maintained at 2.8%. It was found that trace nanoparticles can weaken the grain boundary segregation of the composite ingot significantly, effectively avoiding the hot cracking that may occur during hot extrusion and FSW. In extruded profiles, nanoparticles promoted the nucleation of η′ precipitates, promoted the dislocation multiplication, and increased the proportions of low-angle grain boundaries (LAGBs) within 2°–15° and high-angle grain boundaries (HAGBs), thereby enhancing the strength. Meanwhile, nanoparticles increased the density of LAGBs and facilitated the precipitation of Guinier–Preston (GP) zones, which facilitated to maintain high plasticity of the extruded profiles of composite. Additionally, nanoparticles can effectively inhibit the abnormal grain growth in nugget zone (NZ) during post-weld heat treatment (PWHT), which strengthened the FSW-ed joint. This work elaborated the multiscale microstructure evolution mechanisms, offering guidance to fabricate Al–Zn–Mg–Cu workpieces with infinitely extensive size as required in actual manufacturing and fantastic mechanical performances. [Display omitted] • Trace in-situ TiC–TiB 2 enhanced performance of large-size Al–Zn–Mg–Cu composite. • TiC–TiB 2 optimized segregation, recrystallization and precipitation behavior. • TiC–TiB 2 inhibited the abnormal grain growth during post-weld heat treatment. • Microstructure evolution and performance improvement mechanisms were revealed. [ABSTRACT FROM AUTHOR]