Precipitation behaviors of multi-scale precipitation strengthened Al–Mg–Si–Cu–Zn alloys controlled by Mg content

In this paper, the effect of the Mg content and the precipitation behaviors in Al–Mg–Si–Cu–Zn alloys is reported. Also, the low strength of 6xxx aluminum alloys is improved by high alloying degree, in which the Mg and Si contents exceed the range of 6xxx aluminum alloys. As a result, the strengths of the alloys are higher than that of 6xxx aluminum alloys. Compared with peak-aged 6016 aluminum alloy, the yield strength and tensile strength of the Al-1.63Mg-1.20Si-0.20Cu-3.00Zn (wt.%) alloy were increased by 112.6 and 97.2 MPa, respectively, due to micron/nanoscale multi-particle strengthening effects. The microscale phase was Mg2Si, and the nano-scale phases were β" and Q′ phases. The alloy also exhibited excellent properties when aged at a higher temperature (185 °C), so it is expected to significantly harden during actual baking processes. This was revealed by the APT analysis in which elements were clamped to each other at a low temperature, while they precipitated more easily at a high temperature. Precipitation kinetics calculations showed that the activation energy of the β" phase decreased upon increasing the Mg content, which promoted precipitation strengthening.