Characterisation of Quasicrystalline Particles in an Isothermally Aged Al–10Mg–0.5Ag (mass%) Alloy

Abstract

The quasicrystalline structure found in the isothermally aged microstructure in an Al-10Mg-0.5Ag (mass%) alloy after solution treated, water quenched and then aged during the time between 20 and 40 min at 240 C has been characterised using transmission electron microscopy, electron microdiffraction and energy dispersive x-ray spectroscopy. The morphology of the quasicrystalline precipitate particles is rhombohedral in shape and those precipitate particles are homogeneously nucleated, and finely and uniformly dispersed in the matrix. The orientation relationship between the quasicrystalline phase and the -Al matrix is as follows; i5 k h011i and i3 k h111i . The quasilattice constant a R of the icosahedral quasicrystalline phase is estimated to be 0:505 AE 0:01 nm from the present 5-fold electron microdiffraction patterns. The lattice parameter a c of the corresponding crystalline cubic approximant is thus calculated to be 1:390 AE 0:028 nm. This is in good agreement with the lattice parameter of the crystalline T phase (Mg 32 (Al,Ag) 49 , a ¼ 1:416 nm). The morphology of the quasicrystalline precipitate particle is consistent with that predicted from the intersection point group 3 3, which was defined by symmetry elements common to the two lattices in the observed orientation relationship. The quasicrystalline particles contain elements of Al, Mg and Ag. The quasicrystalline precipitate particles, which are the metastable phase, appear to be the primary strengthening phase in the Al-10Mg-0.5Ag (mass%) alloy aged at 240 C.

Identification of Metastable Rod-Like Particles in an Isothermally Aged Al–10Mg–0.5Ag (mass%) Alloy

“…It thus remains that precipitate microstructures and precipitate phases in the ternary Al-Mg-Ag alloys during isothermal ageing are not thoroughly and convincingly understood. The purpose of this paper is to report results of a detailed microstructures examination of the metastable rod-like T precipitates phase transformed from the metastable quasicrystalline precipitate phase [13][14][15][16] during conventionally isothermal ageing process in an Al-10Mg-0.5Ag (mass%) alloy. Characterisation of structure and morphology of the metastable rod-like T precipitates phase was carried out using transmission electron microscopy with electron diffraction techniques.…”

Observation of Beta Phase Particles in an Isothermally Aged Al-10 mass%Mg Alloy with and without 0.5 mass%Ag

“…Early studies [8][9][10] suggested that the decomposition process might be summarised as follows: Supersaturated solid solution ( 12) as the equilibrium phase in the aged Al-Mg-Ag alloy. Recent studies of the microstructural observations by transmission electron microscopy (TEM), 13,14) however, revealed the formation of both the quasicrystalline phase rather than T 0 phase in the early stages and the equilibrium phase in over-aged conditions in Al-10Mg-0.5Ag (mass%) alloy.…”

Identification of β Phase Particles in an Isothermally Aged Al–10 mass%Mg–0.5 mass%Ag Alloy

“…As can be seen from these TEM micrographs, no fine-scale, uniformly distributed rod-like h110i particles, that were principally dispersed intermetallic compounds in the maximum hardness condition (i.e. 0.5 h at 240 C), [23][24][25][26] were observed, and they were replaced by coarse-scale precipitate particles, with two distinguishable morphologies. The dom- inant morphology was that of coarse-scale, irregularly globular particles, while there was a small volume fraction of finer-scale, spherical precipitates.…”

“…0.5 h at 240 C), [23][24][25][26] microstructures contained fine scale, uniformly distributed faceted particles. At the peak-aged stages of ageing (e.g.…”