Structural modifications and electron beam damage in aluminium alloy precipitate θ'–AL₂

Abstract

The θ ′ -Al2Cu phase in an Al-4Zn-2Cu-1Mg-0.7Si (wt.%) alloy was investigated by means of scanning transmission electron microscopy. With our specific alloy composition, the phase is often formed with stacking faults on {101} θ ′ and {001} θ ′ planes. The stacking faults on {101} θ ′ planes are often regularly spaced and create a previously unreported superstructure. Structural damage by electron irradiation is observed, even at a low acceleration voltage of 80 kV. The damage is more pronounced in the θ ′ precipitates with stacking faults, which agrees with theoretical calculations of knock-on scattering cross-sections. These two very different forms of disruptions of the θ ′ structure are linked to its spacious interstitial sites and the ease at which Cu atoms diffuse into and between them.

Precipitation behavior in an Al–Cu–Mg–Si alloy during ageing

“…For θ' plates with thickness about 1-1.5 nm the connection with the GPB zone units is often observed at the semi-coherent (narrow) interface of the plates. The bulk structure of these thin θ' plates is defect-free and matches with the well-established Silcock model [12][13][14]49,53]. Two columns, marked with red circles in Fig.…”

“…Fig. 7b shows the presence of the θ' plates with stacking faults [53]. The formation of the θ'-C complexes early described in [32] have been also found (Fig.…”

The Crystallography of Aluminum and Its Alloys

“…Density functional theory (DFT): (234,242,260,261,271,276,307,328,330,339,343,346,350,351,358,378,408).…”

Unique hybrid precipitate structures forming in an Al–Cu–Mg–Si alloy

“…[5] that other AlMgSiCu-type precipitates can form at the edge of semi-coherent interfaces of the q 0 -phase plates containing different types of faults described in detail in Ref. [23].…”