Effects of Zn addition on the age hardening behavior and precipitation evolution of an Al-Mg-Si-Cu alloy

The effects of Zn on the age hardening behavior and corresponding microstructure of an Al-0.9Mg-0.8Si-0.2Cu (wt%) alloy were investigated by hardness testing, transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP). During aging for up to 8 h at 170 °C (peak hardness condition), the addition of Zn does not alter the precipitation sequence of the Al-Mg-Si alloy, which can be expressed as: supersaturated solid solution → solute clusters → GP zones → β″. The Zn does not significantly partition into clusters or precipitates, and the majority of Zn remains in the Al matrix, prompting the formation of solute clusters during the early stage of aging and subsequently stimulating the transformation from solute clusters to GP zones to β″ precipitates. The characterization of precipitation evolution caused by Zn addition correlates well with the observed enhanced age hardening response.