The quasi-crystalline phase in the Mg—Al—Zn system

Crystallographic relationship of orthorhombic φ-Al5Mg11Zn4 phase to icosahedral quasicrystalline phase

“…It has been demonstrated that on rapid solidification an alloy with a composition of the Bergman phase forms into an icosahedral phase [12,13]. Icosahedral phase is also formed on conventional solidification in alloys such as ZA84 [14].…”

Precipitation and Hardening in Magnesium Alloys

“…For Mg-Zn-Al alloys with compositions lying in the (a-Mg + /) two-phase field and produced by high-pressure die casting or permanent mold casting, recent studies using TEM and convergent-beam electron diffraction patterns [107,108] indicate that primary intermetallic particles in the as-cast condition have a quasi-crystalline structure (point group of m " 3 " 5, quasi-lattice parameter~0.515 nm) and a composition of approximately Mg 55 [109] and Mg 32 (Al,Zn,Cu) 49 [110] intermetallic alloys, but it is smaller than the that (0.528 nm) reported for the icosahedral Mg 38.5 Al 52 Zn 9.5 phase in Al-Mg-Zn alloys. [111] Even though the equilibrium T phase is often regarded as the crystalline approximant of the icosahedral phase, [112] the metastable quasi-crystalline phase does not transform to the T phase after prolonged heating at elevated temperatures such as 598 K (325°C).…”

Evidence from x-ray and neutron powder diffraction patterns that the so-called icosahedral and decagonal quasicrystals of MnAl 6 and other alloys are twinned cubic crystals

“…The quenched alloy was found to give an electron diffraction photograph with a 5-fold axis by Ramachandrarao and Sastry (14) and by Rajasekharan et al (15), who also published its x-ray powder diffraction curve. I have measured the positions of the peaks on this curve, with the results shown in Table 3 provides additional support of the postulated 820-atom primitive cubic structure.…”