Characterization of precipitation behaviors in a non-stoichiometric Cu-24.5at.%Al-19.4at.%Mn alloy

Scanning and transmission electron microscopy examinations of Cu-24.5at.% Al-19.4at.%Mn (similar to Cu2.2Mn0.8Al) alloy were performed after aging at temperatures ranging from 350 °C to 700 °C for various durations. It was observed that only γ-brass type and L-J phases were formed after aging at or below 400 °C. On the other hand, the β-Mn phase was formed after aging at temperatures ranging from 500 °C to 650 °C. It is noteworthy that the precipitation behaviors of the γ-brass type and β-Mn phases are different at different aging temperatures. This remarkable result differs from those reported in previous studies on the Cu3 − XMnXAl alloys with X ≦ 1.

Research Highlights
► Precipitation behaviors in a Cu2.2Mn0.8Al alloy shows different results from those reported in previous studies on the Cu-A-lMn alloys.
► The γ-brass type precipitate occurs at temperatures ranging from 350 °C to 500 °C revealing different precipitation characteristics.
► The β-Mn phase formed after aging at 500 °C to 650 °C shows different precipitation behaviors as well.
► L-J phase having an orthorhombic structure could be always observed in the as-quenched and aged conditions.