Ya Li

The creep aging behavior and mechanical properties of Al-Zn-Mg-Cu alloys were studied via microalloying with Yb at different creep aging temperatures (120°C, 160°C, and 200°C), by the combined use of electron/atom microscopic characterization and first-principles calculations. The findings demonstrated that the presence of Yb elements led to the formation of vacancy-rich clusters, where Yb atoms captured vacancy atoms, thereby decreasing the concentration of free vacancies at creep temperature of 120°C. This hindered the diffusion rate of solute atoms, reducing creep strain and the number of nucleation sites, resulting in a decline in the yield strength of Al alloy. As the creep temperature rose to 160°C, Yb-vacancy clusters dissolved back into the matrix in the early stages of aging, releasing previously trapped vacancies. This caused increased lattice distortion within the Al alloy, creating favorable conditions for solute atom diffusion, prompting fine and dispersed η' phase precipitation, and boosting the yield strength and creep strain of the alloy. The incorporation of the Yb element resulted in the transformation of grain boundary precipitates from a continuous to an intermittent distribution, with an associated increase in precipitate size and PFZ width, thereby enhancing the plasticity of the Al-Zn-Mg-Cu alloy. The 0.3Yb alloy displayed superior creep strain and mechanical properties, with a yield strength of 662.4 MPa, an elongation of 11.6%, and a creep deformation of 0.088% at creep temperature of 160°C. The present study suggests that microalloying with Yb is expected to be an effective strategy to simultaneously improve the creep strain and strength of Al-Zn-Mg-Cu alloy under creep aging.