Abstract
In this work, the ageing of some Al-Mn-Cu-Be alloys was investigated in the temperature range in which predominantly icosahedral quasicrystalline (IQC) precipitates can form. The alloys were cast into a copper mould, directly aged (T5 heat treatment) between 300 and 440 °C for different times. Afterwards, they were examined using scanning and transmission electron microscopy, X-ray diffraction and hardness testing. The main aim of the work was to determine the conditions at which a high number density of spherical icosahedral quasicrystalline precipitates can form. The highest number density of IQC precipitates was obtained at 300 °C after prolonged ageing. The spheroidal precipitates had a diameter less than 20 nm. The size of IQC precipitates increased with the increasing temperature, and in addition, decagonal quasicrystalline precipitates appeared. The time to maximum hardness decreased strongly with increasing ageing temperature. The IQC precipitates can form in a fairly broad temperature range in Al-Mn-Cu-Be alloys and that by varying ageing temperature and duration, rather different distributions of precipitates can be obtained. The presence of precipitates caused rather strong aluminium alloys and fast work hardening during initial plastic deformation.
Highlights
Quasicrystals were discovered in Alloy w (Al)-Mn alloys [1]
Since an icosahedral quasicrystalline phase (IQC) in these and similar alloys is metastable [2], the alloys have been predominantly fabricated by rapid solidification and compacted [3]
Rapid solidification enables the formation of very small particles, which can slightly coarsen during compaction, but a fine distribution of quasicrystalline particles can provide high strength [4]
Summary
Quasicrystals were discovered in Al-Mn alloys [1]. Since an icosahedral quasicrystalline phase (IQC) in these and similar alloys is metastable [2], the alloys have been predominantly fabricated by rapid solidification and compacted [3]. Rapid solidification enables the formation of very small particles, which can slightly coarsen during compaction, but a fine distribution of quasicrystalline particles can provide high strength [4]. A fine distribution of particles can be obtained by precipitation hardening, which is a typical hardening process in many aluminium alloys [9,10,11,12]. According to the best of the authors’ knowledge, there are no commercial alloys that would be mainly strengthened by icosahedral quasicrystalline particles. Coherent IQC precipitates predominantly formed on the dislocations and dislocation walls, and were relatively rare
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