Microstructural evolution in a Cu–24.5 at.% Al–19.4 at.% Mn alloy inside the miscibility gap

When a Cu–24.5 at.% Al–19.4 at.% Mn alloy was aged at 300 °C for 48 h, the microstructure was a mixture of (D03 + L21 + L–J) phases. However, as the present alloy was aged at 350 °C for moderate times, the microstructure revealed a coexistence of (D03 + L21 + γ-brass + L–J) phases. The γ-brass phase started to occur on the a/2〈1 0 0〉 anti-phase boundaries (APBs) initially as aged at 350 °C, and then grew along the 〈1 0 0〉 crystallographic directions after prolonged aging. Furthermore, the formation of L–J phase was found to be concerned with the redistribution of Mn and/or Al alloying elements during aging.