Influence of copper, calcium and strontium on the formation of quasicrystals in Al-Mn-based alloys

In this study, the effect of adding calcium or strontium to Al-Mn and Al-Mn-Cu alloys on the formation of quasicrystals (QCs) is investigated. The alloys were cast in a massive copper mould with a cavity diameter of 3 mm. The cast alloys were characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and electron backscatter diffraction. The addition of either calcium or strontium to Al-Mn and Al-Mn-Cu alloys promotes the formation of icosahedral QCs (IQCs). The results also show that neither calcium or strontium are integral part of the QC phases formed in these alloys. The results further indicate considerable differences in the composition of decagonal QC (DQC) phases in Al-Mn-Cu alloys without and with either calcium or strontium, whereas the electron-atom ratio according to Mizutani shows almost negligible differences. The effectiveness of calcium and strontium in promoting the formation of IQCs is attributed to a reduced surface tension of the Al-based melt. This consequently leads to a decrease in the critical radius for nucleation of IQCs. • Calcium and strontium were added into an Al-Mn and Al-Mn-Cu alloy systems. • Alloys were cast into a copper mould. • The addition of calcium or strontium promotes the formation of QCs. • Calcium and strontium are not present in QCs. • Effectiveness of both elements is attributed to a reduction in the surface tension.