Abstract:By tensile test and transmission electron microscopy, the ageing precipitation behavior of an experimental high purity Al-Cu-Mg-Ag type alloy was investigated during a long period of ageing time. The results show that the experimental alloy has good ductility and heat resistance. Ω phase is the key hardening precipitate. The strength of the ageing alloy underwent at 185 ℃ for 50 h is only decreased by 6% to 7% of the peak-aged alloy, and the elongation ratio of δ10 retains up to 8%. Under condition of peak-aged, high misfit strain exists near Ω/α interface and leads to dislocation at the fine laths of Ω phase, which actually serve as favorable heterogeneous nucleation sites for secondary-precipitated phase θ′. As ageing time prolongs, larger Ω phase and mostly metastable θ′ phase including primary and secondary precipitate transmit to equilibrium θ phase, but the transmission procedure of Ω→θ is much slower than that of θ′→θ.

Key words: Al-Cu-Mg-Ag alloy; Ω phase; primary-precipitated phase; secondary-precipitated phase; coarsening