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

Abstract

Crystal structures of hybrid precipitates have been analysed by atomic-resolution scanning transmission electron microscopy in an aged AleCueMgeSi alloy. A new unique hybrid precipitate (UHP) has been found as rod-shaped discrete particles along C100D Al in bulk aluminium matrix. The UHP consists of a core with local 4-fold symmetry surrounded by GPB zone unit pillars often combined with monoatomic Cu layers in fcc-Al matrix. A certain atomic configuration fragment of the UHP structure is often seen to inter-grow with other hybrid precipitate complexes consisting of diverse phases belonging to the AleCu eMgeSi and AleCu alloy systems. Density functional theory (DFT) calculations performed on a discrete UHP showed that the most energetically favorable core configuration resembles a b 00 -eye from the Al eMgeSi system rotated 45 + C in respect to its usual orientation with the fcc-Al matrix.

The unique hybrid precipitate in a peak-aged Al-Cu-Mg-Ag alloy

“…Foils for transmission electron microscopy (TEM) were prepared using conventional methods [11] and studied in two microscopes operated at 200 kV: a JEOL JEM-2100F and a JEOL ARM-200F, the latter being double aberration corrected. The TEM settings given in Table S1 were used for acquisition of STEM images [12] .…”

Atomic Structure of Hardening Precipitates in Al–Mg–Si Alloys: Influence of Minor Additions of Cu and Zn

“…Zn is also observed to have a more distinct effect on precipitate crystal structures that, to the best of the authors’ knowledge, have not been described previously; see Figures c, b,d, and a,b. It promotes the formation of defects with extended 2-fold symmetry and mirror plane configurations, which is not observed in precipitates nucleated in pure Al–Mg–Si alloys or with Ag, Li, and Cu additions. ,,− ,,,,− Moreover, Zn shows less tendency than Cu to occupy the β″/Al matrix interface periodically, but Zn incorporates preferentially on the Si 2 , Si 3 /Al sites of the β″ structures, which also suppresses misfit dislocations; see Figure c,d. It is interesting to note that Zn suppressed misfit dislocations even in the precipitates comprised of β″ and β′′ 2 structures; see Figure a.…”

The Effect of Cu Addition on the Precipitation Sequence in the Al-Si-Mg-Cr Alloy

“…However, the distribution of Si and Mg exactly coincides with other needleshaped phases, as shown by the red arrows in Figure 9d,e. They are invisible in the HAADF image due to the very close atomic numbers of Mg (12), Al (13), and Si (14). In the TEM results, these phases are estimated to be β′-Mg2Si precipitates.…”

“…As Li et al [12] reported, through a certain heat treatment consisting of solution treatment and artificial aging, the strength of Al-Si cast alloys can be increased considerably. In recent years, it has been reported that adding Cu to Al-Mg-Si alloys can enhance the age-hardening effect of the alloy [13][14][15][16]. Sunde et al [15] found that relatively small changes in the Cu level and the Si:Mg ratio had a significant effect on the resulting distribution of precipitate phases, their structural evolution, and their thermal stability.…”