Synergistic Enhancement of Strength and Plasticity in Al–Mg–Si Alloys by Slow-Diffusing Elements Cr, Ti, and Zr

The interaction between fast-diffusing and slow-diffusing elements in aluminum alloys is critical for enhancing alloy performance. This study investigates the effect of adding slow-diffusing elements Cr, Zr, and Ti on the microstructure characteristics, aging precipitation behavior, and mechanical properties of Al–Mg–Si alloys. The results show that the simultaneous addition of Cr and Zr promotes recrystallization grain refinement and significantly enhances the Orowan strengthening effect. Specifically, Cr effectively inhibits the coarsening of Fe-containing dispersoids, transforming α-Al(MnFe)Si dispersoids into a larger quantity of α-Al(MnFeCr)Si dispersoids with an average diameter of approximately 126 nm. Zr addition forms (Al, Si)₃Zr dispersoids with diameters ranging from 30 to 60 nm, which further reduce the average dispersoid size and increase the volume fraction. In alloys with the simultaneous addition of Cr, Zr, and Ti, the distribution of Cr and Ti solutes in the matrix helps reduce the diffusion rate of quenching vacancies, thereby suppressing the rapid coarsening of intragranular and intergranular precipitates during aging. This results in a reduction in the width of the PFZs and the promotion of early precipitate nucleation, which enhances the precipitation strengthening effect. Consequently, the alloy exhibits an optimal balance between strength and plasticity, with UTS, YS, and δ values of 417 ± 2 MPa, 371 ± 6 MPa, and 17.8 ± 0.3 pct, respectively.