Microstructural evolution in Al–Mn–Cu–(Be) alloys

Abstract

This study investigates the effects of alloying elements on the microstructural evolution of Al-rich Al–Mn–Cu–(Be) alloys during solidification, and subsequent heating and annealing. The samples were characterised using scanning electron microscopy, energy dispersive X-ray spectroscopy, synchrotron X-ray diffraction, time-of-flight secondary-ion mass spectroscopy, and differential scanning calorimetry. In the ternary Al₉₄Mn₃Cu₃ (at%) alloy, the phases formed during slower cooling (≈1 K s⁻¹) can be predicted by the known Al–Mn–Cu phase diagram. The addition of Be prevented the formation of Al₆Mn, decreased the fraction of τ₁-Al₂₉Mn₆Cu₄, and increased the fraction of Al₄Mn. During faster cooling (≈1000 K s⁻¹), Al₄Mn predominantly formed in the ternary alloy, whereas, in the quaternary alloys, the icosahedral quasicrystalline phase dominated. Further heating and annealing of the alloys caused an increase in the volume fractions of τ₁ in all alloys and Be₄Al (Mn,Cu) in quaternary alloys, while fractions of all other intermetallic phases decreased. Solidification with a moderate cooling rate (≈1000 K s⁻¹) caused considerable strengthening, which was reduced by annealing for up to 25% in the quaternary alloys, while hardness remained almost the same in the ternary alloy.

Keywords:

• aluminium
• quasicrystal
• microstructure
• beryllium

Acknowledgements

We would like to thank Dr. Tonica Bončina and Dr. Peter Panjan for their kind assistance during indentation measurements. Rok Šulek (UM FS) is acknowledged for the vacuum melting and casting of alloys. We acknowledge Elettra, Sincrotrone Trieste, and the European Commission for reimbursement under EU contract RII3-CT-2004-506008 (IA-SFS), proposal 20090314. This work was also supported by the European Commission – Research Infrastructure Action under the FP6 “European Integrated Activity of Excellence and Networking for Nano and Micro-Electronics Analysis.” Project Number “026134 (RI3) ANNA.” This work was partly financed from the research programme P2 - 0120, of the Slovenian Ministry of Higher Education and Science.