Precipitation microstructure in Al-Si-Mg-Mn alloy with Zr additions

The precipitation microstructure of Al-10Si-0.5 Mg-0.5Mn (wt%) alloys with different Zr additions was investigated. The β-type (i.e. Mg ₂Si) phase was observed to be dominant in the precipitation microstructure. Furthermore, the Q-Al ₅Cu ₂Mg ₈Si ₆ phase and the π-Al ₈Mg ₃FeSi ₆ phase were also observed to be the dominant thermodynamically stable precipitates at 180 °C. The main strengthening effect can be attributed to the Q-Al ₅Cu ₂Mg ₈Si ₆ and β-type (i.e. Mg ₂Si) precipitates due to the fact that the π-Al ₈Mg ₃FeSi ₆ phase is relatively large in size, plate-like in morphology, and low in number density and thereby volume fraction. More importantly, the Zr addition into the Al-Si-Mg-Mn alloys causes the precipitation to start at a lower temperature during ageing, which can be due to the grain refinement effect by Zr addition and thereby enhanced diffusion. This paper provides some insights in precipitation microstructure and thereby shortening the ageing treatment at a relatively low ageing temperature.