Quasicrystals in an aluminium alloy matrix and the transformation to α‒AlMnSi via intermediate stages

Abstract

Abstract During heat treatment of an industrially produced Al high-Mn alloy, small particles of the quasicrystalline icosahedral AlMnSi phase were precipitated, with a definite orientation relation to the Al matrix. Upon further annealing, the particles coarsen and transform, through intermediate stages into the cubic α-AlMnSi phase. The intermediate stage is characterized by faults on {110}α planes, with fault vectors of type δ=1/16[530] as revealed by diffuse streaks in electron diffraction patterns. The fault vector component normal to the fault plane produces displacement of diffraction spots relative to the α-AlMnSi reflections. The faults produce a local arrangement of MacKay icosahedra that can be described by a rhombohedron (α′) which is complementary to the rhombohedron which constitutes the primitive unit cell of the bcc packing of MacKay icosahedra in α-AlMnSi. A model for a composite defect, built from three {110} faults is constructed.