Formation of a Quasicrystalline Phase in Al–Mn Base Alloys Cast at Intermediate Cooling Rates

Al-rich 94Al–6Mn and 94Al–4Mn–2Fe alloys were suction-cast to evaluate thefeasibility of obtaining bulk quasicrystal-strengthened Al-alloys at intermediatecooling rates alloyed with non-toxic, easily accessible and affordable additions.The influence of different cooling rates on the potential formation of a quasicrystallinephase was examined by means of scanning and transmissionelectron microscopy, X-ray diffraction and differential scanning calorimetry.Increased cooling rates in the thinnest castings entailed a change in samplephase composition. The highest cooling rates turned out to be insufficient toform an icosahedral quasicrystalline phase (I-phase) in the binary alloy. Instead,an orthorhombic approximant phase occurred (L-phase). The addition of Fe tothe 94Al–6Mn binary alloy enhanced the formation of a quasicrystalline phase.At intermediate cooling rates of 102–103 K/s, various metastable phases wereformed, including decagonal and icosahedral quasicrystals and their approximants.Rods (1 mm in diameter) composed of I-phase particles embedded in Almatrix exhibited a hardness of 1.5 GPa, much higher than the 1.1 GPa of 94Al–6Mn