Al-rich region of Al–Cu–Mn

Abstract

The Al–Cu–Mn alloy system was studied above 45 at.% Al between 550 and 910 °C by scanning electron microscopy, powder X-ray diffraction and differential thermal analysis. A wide ternary region of the so-called β-phase extending along ∼50 at.% Al was confirmed. It has a CsCl-type structure with a≈0.292–0.298 nm. The total γ1/γ2-region extends from Al–Mn up to ∼17 at.% Cu and the high-temperature T-Al3Mn phase (Pnma, a≈1.48, b ≈ 1.24, c ≈ 1.25 nm) extends up to ∼15 at.% Cu. The so-called R-phase (Bbmm, a≈2.41, b ≈ 1.25, c ≈ 0.76 nm) was found to exist in a compositional region of Al74-80Cu5-12.5Mn12.5-18. The ternary phase earlier reported at Al57.9Cu26.3Mn15.8 was confirmed. It exists below 697 °C in a compositional region of Al55-58Cu29-37Mn7.5-14. The decagonal D3-phase was concluded to be stable in a compositional region of Al61.5-68.5Cu19-29.5Mn9-16. Below 631 °C an fcc phase (a = 0.5814 nm) was revealed around ∼ Al60Cu36.5Mn3.5. Partial isothermal sections at 550, 600, 650, 750, 850 and 910 °C were constructed.