Accurately measured precipitate–matrix misfit in an Al–Mg–Si alloy by electron microscopy

Wenner, Sigurd; Holmestad, Randi

doi:10.1016/j.scriptamat.2016.02.031

Cited by 47 publications

(14 citation statements)

References 20 publications

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“…This precipitate phase has a monoclinic unit cell with a = 1.516 nm, b = 0.405 nm, c = 0.674 nm, and angle β = 105.3° [26]. The needles are coherent with the matrix along their length, and strain their local matrix neighbourhood in their lateral dimensions [27]. This alloy has been used in several other studies, including Khadyko et al [18] and Frodal et al [28], and serves as a model alloy, which also has extensive industrial applications.…”

Section: Introductionmentioning

confidence: 99%

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Christiansen

Marioara

Marthinsen

et al. 2018

Materials Characterization

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Scanning precession electron diffraction and automated crystal orientation mapping in a transmission electron microscope (TEM) have been applied to quantitatively study the crystal orientation of precipitate free zones (PFZs) of four GB regions in an AA6060 alloy in peak aged condition (temper T6) after uniaxial compression to 20% engineering strain. The PFZ width in the alloy is found to be w = 170 ± 40 nm. The results show that some PFZs develop significant misorientations relative to their parent grain, and represent, to the best knowledge of the authors, the first quantitative evidence of this. This misorientation may either be constant inside a particular PFZ, making it appear like a band or a very elongated subgrain, or be partitioned in discrete regions with a diameter comparable to the PFZ width, making the former PFZ into a collection of small grains. The band-like PFZ observed in this work had a misorientation relative to its parent grain of ∼ 7°, while the grain-like PFZ had grains with misorientations between ∼ 12°and ∼ 20°r elative to its parent grain. The other PFZs that were observed had only limited misorientations relative to their parent grains, and had either dislocations perpendicular to the GB plane or a dislocation wall at the transition region. A general TEM study of the material at various engineering strains was also conducted and suggests that grain-like PFZs are more frequent for larger strains, indicating that the different PFZ features are likely due to different strain localisation in individual PFZs. This localisation is expected to be influenced by the orientation of the loading axis relative to crystal orientations and GB planes. It is also suggested that the different PFZ features engender different work hardening rates and possibly affect nucleation of intergranular fracture. The results support previous studies on the microstructure evolution of PFZs in age-hardenable aluminium alloys during deformation.

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Section: Introductionmentioning

confidence: 99%

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Christiansen

Marioara

Marthinsen

et al. 2018

Materials Characterization

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“…The c of b¢¢/Al-matrix interface is difficult to determine due to its dependency on precipitate size and interfacial anisotropy. [2,38] As an early stage metastable precipitate, the c of b¢¢/Al-matrix interface is considered small as a result of a full coherency of b¢¢ with the Al matrix along the precipitate needle direction and semi-coherency along a and c axes. In the present simulation, a value of 0.05 J/m 2 for c was adopted, which is very close to the value of 0.045 J/m 2 utilized in Du's multi-class approach.…”

Section: A Model Prediction Of B¢¢ Precipitationmentioning

confidence: 99%

“…THE nucleation and growth kinetics of secondary phases during artificial aging heat treatment are crucial in enhancing the mechanical properties of various alloy systems. [1][2][3][4][5][6] 6xxx and 7xxx aluminium alloys can generally be precipitation strengthened via artificial aging, wherein complex precipitation of multiple precipitates occurs, contributing to the hardening of the material. [5,[7][8][9][10][11] The extent of precipitation strengthening is largely determined by the precipitate shape, size, and number density.…”

Section: Introductionmentioning

confidence: 99%

Modelling the Age-Hardening Precipitation by a Revised Langer and Schwartz Approach with Log-Normal Size Distribution

Zhao

Gouttebroze

et al. 2020

Metall Mater Trans A

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A new numerical modelling approach integrating the Langer and Schwartz approach and log-normal particle size distribution has been developed to depict the precipitation kinetics of age-hardening precipitates in Al alloys. The modelling framework has been implemented to predict the precipitation behavior of the key secondary phases in 6xxx and 7xxx Al alloys subjected to artificial aging. The simulation results are in good agreement with the available experimental data in terms of precipitate number density, radius, and volume fraction. The initial shape parameter of the log-normal size distribution entering the modeling framework turns to play an important role in affecting the later-stage evolution of precipitation. It is revealed that the evolution of size distribution is not significant when a small shape parameter is adopted in the modelling, while an initial large shape parameter will cause substantial broadening of the particle size distribution during aging. Regardless of the magnitude of shape parameter, a broadening of the particle size distribution as predicted by the present model is in agreement with experimental observations. It is also shown that large shape parameter will accelerate the coarsening rate at later aging stage, which induces fast decreasing of number density and increased growth rate of mean/critical radius. A comparison to the Euler-like multi-class approach demonstrates that the integration of more realistic log-normal distribution and Langer and Schwartz model make the present modelling faster and equivalently accurate in precipitation prediction.

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“…From such images lattice strains can be measured using either real-or Fourier-space methods (such as geometric phase analysis), which can be verified by density functional theory calculations (DFT). This method is now well established and can aid systematic studies across large numbers of precipitates with increased accuracy [2]. A similar approach was followed to obtain multi-scan EDX elemental maps at atomic resolution.…”

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confidence: 99%

Mapping the Chemistry Within, and the Strain Around, Al-alloy Precipitates at Atomic Resolution by Multi-frame Scanning Transmission Electron Microscopy

Jones

Wenner²,

Nord³

et al. 2017

Microsc Microanal

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Al-Mg-Si(-Cu) alloys, used primarily in the transportation sector, are strengthened by nano-sized precipitate particles. There is a plethora of possible phases, depending on which elements are added to the alloy and how the material is heat treated. Here we present results from the S, β'', β'Ge and Q' phases, which all form rod-shaped precipitate with typical dimensions 7x7x50 nm. These phases are meta-stable, which means that they cannot exist outside the Al matrix.To fully understand the properties of these precipitates, both structural and chemical information is needed at the atomic scale. Fortunately both of these data are available using the scanning transmission electron microscope (STEM).When viewed down a {100} zone-axis, annular dark-field (ADF) images of rod-like precipitates can be recorded with sub-Angstrom resolution and the locations of atomic columns identified with picometre precision. However, obtaining high-quality atomic-resolution chemical maps is a compromise between collecting sufficient signal, while minimising sample damage from the electron dose. Classically the experimentalist has had only one parameter, beam current, to do this. Recently with the advent of fast and robust software tools for the non-rigid registration (scan-distortion correction) of multi-frame data [1], a new regime has opened up for the operator where both dose-per-frame and total-dose can be varied independently. Several studies now propose dose-rate as the critical parameter in minimising sample damage.From high-speed multi-frame ADF image acquisition and processing we are able to map column positions with picometre scale precision (Figure 1). From such images lattice strains can be measured using either real-or Fourier-space methods (such as geometric phase analysis), which can be verified by density functional theory calculations (DFT). This method is now well established and can aid systematic studies across large numbers of precipitates with increased accuracy [2].A similar approach was followed to obtain multi-scan EDX elemental maps at atomic resolution. The separate spectral volumes were aligned, corrected for scanning distortion and averaged. Figure 2, shows the experimental detectability of various elemental signals for the experimental conditions used and guides the experiment design. To increase the signal-to-noise ratio of weak elemental signals, the known symmetry of the precipitate phases was further exploited to yield 'symmetry averaged chemical maps'. These identify all the elements clearly for each type of precipitate without the need for noise filtering [3].

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Accurately measured precipitate–matrix misfit in an Al–Mg–Si alloy by electron microscopy

Cited by 47 publications

References 20 publications

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Modelling the Age-Hardening Precipitation by a Revised Langer and Schwartz Approach with Log-Normal Size Distribution

Mapping the Chemistry Within, and the Strain Around, Al-alloy Precipitates at Atomic Resolution by Multi-frame Scanning Transmission Electron Microscopy

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