Precipitation Behavior of the Metastable Quasicrystalline I-Phase and θ′-Phase in Al-Cu-Mn Alloy

Abstract

The precipitation behavior and mechanical properties for conventionally solidified Al-2.0wt.%Cu-2.0wt.%Mn alloy were studied. The supersaturated aluminum-based solid solution, CuAl2, Al6Mn and Al20Cu2Mn3 phases of solidification origin were identified after casting. The high temperature ageing of as-cast samples (T5 treatment) in a temperature range of 300–350 °C led to the formation of the metastable θ′ phase and equiaxed precipitates of the quasicrystalline-structured I-phase. The θ′ phase demonstrated a high size stability in a studied temperature range with a mean length of ~300 nm and a mean thickness of ~24 nm. A mean size of the I-phase precipitates varied in a range of ~30–50 nm depending on the treatment regimes. The rod-shaped T-phase precipitates were formed with an increase in ageing temperature to 400 °C. Mechanical properties were analyzed at room temperature in a solid solution-treated state. The increased yield strength at room temperature and 200–300 °C were observed after ageing at 300 °C for 148 h.