Enhanced aging precipitation behavior and mechanical properties of 6022 Al–Mg–Si alloy with Zr addition

The age-hardenable Al–Mg–Si alloys are mainly strengthened by the nanoscale precipitates during artificial aging. In this study, we find that the addition of trace Zr (0.08 and 0.13 wt%) to Al-1.0Mg-1.2Si (6022) alloy can effectively enhance precipitation kinetics and age-hardening response. Additionally, the Fe-containing phases and grain size are also significantly refined due to Zr addition. The 0.13 Zr alloy has a better combination of yield strength (∼342 MPa) and fracture elongation (∼17.3%) at peak-aged state compared with the Zr-free alloy (∼307 MPa, ∼14.0%). The participation of Zr atoms into Mg–Si precipitates is first found by the atom probe tomography (APT) characterization, implying that Zr participates in the nucleation of β" phases. Accordingly, the size and volume fraction of β" phases in the peak-aged 0.13 Zr alloy are both increased based on the APT quantitative analysis, which results in enhanced yield strength at peak-aged conditions. Moreover, nano-sized (Al, Si)3Zr dispersoids in high number density also provide additional precipitation strengthening. Our work may provide a new design strategy for obtaining Al–Mg–Si alloys with fine microstructure and high performance.