Effect of in-situ ZrB2 nanoparticles on microstructure and mechanical properties of friction stir welding joints in 7N01 matrix composites

In this paper, in-situ nanoparticles ZrB2 were introduced to improve the mechanical properties of Friction Stir Welding (FSW) joints in 7N01 matrix composites. The recrystallization driving force was increased induced by ZrB2 particles. Modified by ZrB2 nanoparticles, the grains in the SZ (stir zone) were refined from 4.8 μm (7N01) to 3.7 μm (ZrB2/7N01), and the recrystallization proportion was increased from 75.1% (7N01) to 85.4% (ZrB2/7N01). Compared with the 7N01 matrix, the ultimate tensile strength (UTS) of friction stir welding joints in ZrB2/7N01 composites was enhanced from 283.3 to 395.6 MPa, the yield strength (YS) was enhanced from 250.8 to 361.4 MPa, elongation was enhanced from 12.7% to 16.2%. The strengthening effect was mainly achieved through the Orowan mechanism. The MgZn2 precipitates grew up under the influence of heat input, the inhibiting effect of precipitates on dislocations movement was weakened. Nanosized ZrB2 particles with superior coarsening resistance can still maintain its morphology and size at high temperature, playing a good strengthening role during the FSW.