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Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Crystallography, Transmission Electron Microscopy, and 8 moreElectron Diffraction, Scanning Transmission Electron Microscopy, High Resolution Transmission Electron Microscopy, Diffraction, Alloy, Materials Characterization, Aluminium, and dark field microscopy
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The effect of natural ageing time before artificial ageing has been investigated in four Al–Mg–Si(–Cu) alloys, with 0.4% Mg + 0.8% Si and 0.8% Mg + 0.4% Si, both with and without 0.14 at.% Cu. The precipitate microstructure was quantified... more
The effect of natural ageing time before artificial ageing has been investigated in four Al–Mg–Si(–Cu) alloys, with 0.4% Mg + 0.8% Si and 0.8% Mg + 0.4% Si, both with and without 0.14 at.% Cu. The precipitate microstructure was quantified by means of transmission electron microscopy. Varying the storage time before ageing for 170 min at 200°C, we observe an initial hardness increase after minutes, a decrease after several hours and another increase after weeks. The hardness decrease was most pronounced in the Mg-rich Cu-free alloy, caused by a reduced precipitate volume fraction. Adding Cu produces finer microstructures, higher hardness and reduces the negative effect of natural ageing regardless of the Mg/Si ratio of the alloy. With 1 week storage, an increase in the fraction of the Cu-containing precipitates L and Q′ was observed in the Cu-containing Si-rich and Mg-rich alloys respectively.
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In the structures of all metastable precipitates in Al-Mg-Cu and Al-Mg-Si alloys, we find that column surrounding of an element column in the needle/lath direction order according to simple principles. Advanced transmission electron... more
In the structures of all metastable precipitates in Al-Mg-Cu and Al-Mg-Si alloys, we find that column surrounding of an element column in the needle/lath direction order according to simple principles. Advanced transmission electron microscopy and DFT calculations support the principles originate with a line defect, which is a segment of a <100>Al column shifted to interstitial positions. We propose the defect aids solute decomposition by partitioning the FCC matrix locally into columns of fewer and higher number of nearest neighbours, which suit smaller and larger size solute atoms, respectively. The defect explains how <100> directionality of the precipitates can arise in a cluster. Ordering of a few defects leads naturally to GPB zones in Al-Mg-Cu and to β'' in Al-Mg-Si.
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Research Interests: Materials Engineering, Condensed Matter Physics, Materials Science, Transmission Electron Microscopy, Scanning Transmission Electron Microscopy, and 9 moreMedicine, Elemental analysis, EELS, Alloy, Precipitation, Aluminium, Interdisciplinary Engineering, Electron Energy Loss Spectroscopy, and Micron
Abstract The Guinier–Preston–Bagaryatsky (GPB) zone and the S phase are the key strengthening precipitates in Al-Cu-Mg alloys. However, how their respective structures evolve during aging has not been fully understood. In this work, the... more
Abstract The Guinier–Preston–Bagaryatsky (GPB) zone and the S phase are the key strengthening precipitates in Al-Cu-Mg alloys. However, how their respective structures evolve during aging has not been fully understood. In this work, the age-hardening behavior and the precipitates in an Al–3Mg–1Cu (wt.%) alloy were investigated by means of Vickers hardness measurements, differential scanning calorimetry, transmission electron microscopy, and density functional theory calculations. A series of common GPB zones and a novel type of GPB zone named “GPBX” were observed in the cold-worked samples aged at 443 K for 20 min. In the subsequent aging, two types of S phases were found to coexist, labeled S-I and S-II phases. Density functional theory calculation results indicate that GPBX zone is stable and the S-I and S-II phases have almost the same formation enthalpy. Common GPB zones transform to S-I phases, while S-II phases are formed from GPBX zones preferentially along dislocation lines. The misorientation angles and morphologies of the S phases are also discussed. GPB zones were confirmed to be structurally linked to β” and U2 precipitates reported in 6xxx (Al-Mg-Si) series Al alloys. The revealed precipitate structures and their interrelationships may provide insights into future alloy design.
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... DOI: 10.1080/14786435.2011.593577 K. Teichmann a * , CD Marioara b , SJ Andersen b , KO Pedersen b , S. Gulbrandsen-Dahl a c , M. Kolar a , R. Holmestad d & K. Marthinsen a Available online: 12 Jul 2011. ... Phil. Mag. , 87: 3385... more
... DOI: 10.1080/14786435.2011.593577 K. Teichmann a * , CD Marioara b , SJ Andersen b , KO Pedersen b , S. Gulbrandsen-Dahl a c , M. Kolar a , R. Holmestad d & K. Marthinsen a Available online: 12 Jul 2011. ... Phil. Mag. , 87: 3385 [Taylor & Francis Online] View all references. ...
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Al-Mg-Si(-Cu) alloys are an important group of age hardening materials and possess some of the more complex precipitation sequences: In Al-Mg-Si, none of the metastable hardening precipitates can be described as weakly distorted versions... more
Al-Mg-Si(-Cu) alloys are an important group of age hardening materials and possess some of the more complex precipitation sequences: In Al-Mg-Si, none of the metastable hardening precipitates can be described as weakly distorted versions of equilibrium phases, while in Al-Mg-Si-Cu, one of the main hardening precipitates is not associated with a unit cell. For both sequences, however, more than a decade of experimental work has revealed that a Si substructure with projected hexagonal symmetry when viewed in precipitate main growth axis projection is shared among all metastable phases. The present work seeks to clarify theoretically the significance of the Si network to phase stabilization while also quantifying the level of similarities among the various phases possessing this structure. Based on these results, very clear suggestions for a common precipitate nucleation mechanism emerge.
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Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.
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The composition of β″ precipitates in an Al–Mg–Si alloy has been investigated by atom probe tomography, ab initio density functional calculations, and quantitative electron diffraction. Atom probe analysis of an Al-0.72% Si-0.58% Mg... more
The composition of β″ precipitates in an Al–Mg–Si alloy has been investigated by atom probe tomography, ab initio density functional calculations, and quantitative electron diffraction. Atom probe analysis of an Al-0.72% Si-0.58% Mg (at. %) alloy heat treated at 175 °C for 36 h shows that the β″ phase contains ∼20 at. % Al and has a Mg/Si-ratio of 1.1, after correcting for a local magnification effect and for the influence of uneven evaporation rates. The composition difference is explained by an exchange of some Si with Al relative to the published β″-Mg5Si6 structure. Ab initio calculations show that replacing the Si3-site by aluminum leads to energetically favorable compositions consistent with the other phases in the precipitation sequence. Quantitative electron nanodiffraction is relatively insensitive to this substitution of Al by Si in the β″-phase.
Research Interests: Engineering, Physics, Materials Science, Applied Physics, Electron Diffraction, and 14 moreHeat Treatment, Crystal structure, Mathematical Sciences, Applied, Physical sciences, Atom probe tomography, Alloy, Precipitation, Microstructures, Ab Initio, Aluminium Alloy, Atom Probe, Ab Initio Calculation, and Magnesium Alloy
Two Al-Mg-Ge alloys with compositions Al-0.87Mg-0.43Ge (at. pct) and Al-0.59Mg-0.71Ge (at. pct) were investigated and compared using high-resolution transmission electron microscopy, annular dark-field scanning transmission electron... more
Two Al-Mg-Ge alloys with compositions Al-0.87Mg-0.43Ge (at. pct) and Al-0.59Mg-0.71Ge (at. pct) were investigated and compared using high-resolution transmission electron microscopy, annular dark-field scanning transmission electron microscopy, and nano-beam electron diffraction. The alloys contained fine needle- and lath-shaped precipitates after aging at 473 K (200 °C) for 16 hours, which produced hardnesses similar to those measured in comparable Al-Mg-Si alloys. The β″ phase was not observed. Instead, hardness was achieved by β′-like and disordered precipitates in the Mg-rich alloy, and U1-like and disordered precipitates in the Ge-rich alloy. In all cases, the fine precipitates had structures containing an ordered near-hexagonal network of Ge atoms with a = b ≈ 0.4 nm, which could be visualized directly in annular dark-field mode. The network is very similar to the recently discovered Si network that relates all precipitate structures in the Al-Mg-Si alloys. The orientation of the precipitate unit cells and the Ge network relative to the Al matrix differed from what has been observed for β′ and U1 in the Al-Mg-Si system.
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Al–Mg–Si alloys are usually formed into their final shape by rolling or extrusion. After extrusion, the aluminium profiles are usually straightened, causing the material to be subjected to a small plastic deformation. This study... more
Al–Mg–Si alloys are usually formed into their final shape by rolling or extrusion. After extrusion, the aluminium profiles are usually straightened, causing the material to be subjected to a small plastic deformation. This study demonstrates the positive effect on strength that can be obtained from such small deformation levels or from only elastically straining the material. Elastic straining of a lean Al–Mg–Si alloy, when performed immediately after solution heat treatment, enhances the material yield strength after artificial ageing to T6. Transmission electron microscopy shows that this effect can be attributed to a higher number density and finer dispersion of the age-hardening precipitate needles. Furthermore, introducing a small plastic deformation of 1% after solution heat treatment results in a comparable strength increase to elastically straining the material. In this case, however, the strength increase is due to the increased dislocation density, which compensates for a ...
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The raw data presented in "Studying GPI zones in Al-Zn-Mg alloys by 4D-STEM" submitted to Materials Characterization September 2021. The code for analyzing the data can be found here: doi.org/10.5281/zenodo.5518852
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The dataset refers to the research article “Precipitation processes and structural evolutions of various GPB zones and two types of S phases in a cold-rolled Al-Mg-Cu alloy” [1]. Transmission electron microscopy (TEM) and density... more
The dataset refers to the research article “Precipitation processes and structural evolutions of various GPB zones and two types of S phases in a cold-rolled Al-Mg-Cu alloy” [1]. Transmission electron microscopy (TEM) and density functional theory (DFT) were used to investigate precipitates in an Al-Cu-Mg alloy aged at 443 K for various times. High-angle annular dark-field scanning TEM (HAADF-STEM) images in <100> Al orientations were analyzed. Characteristic contrast and symmetries of columns [2] yielded atoms and positions, used to build precipitate models which could be refined and compared with solid solution reference energies. A calculation cell is an Al supercell compatible with symmetry and morphology of a precipitate, which is fully or partly surrounded by Al, allowing periodicity continuation via neighbor cells. The given crystallographic data include two S-phase variants and Guinier–Preston–Bagaryatsky (GPB) zones, of which the “GPBX” is new.
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Results of theoretical atomistic ab initio investigations of the interior of the [100]Al interface between Al and the C-type plate precipitate observed in the Al-Mg-Si-Cu alloy system are presented. Guidelines for a consistent model... more
Results of theoretical atomistic ab initio investigations of the interior of the [100]Al interface between Al and the C-type plate precipitate observed in the Al-Mg-Si-Cu alloy system are presented. Guidelines for a consistent model description of the strain field evolution along the interface are provided. This scheme can be used, in conjunction with an interface configuration study, for predicting theoretically, at the atomic level, the maximum dimensions, shapes, and full interfacial energies of isolated coherent precipitates with compositionally abrupt interfaces.
Precipitate types that form in an Mg-rich Al-Mg-Si-Cu alloy with 0.12 wt% Ag additions, during over-aging at 200C, have been analysed by Annular Dark Field Scanning Transmission Electron Microscopy (ADF-STEM). It was found that most... more
Precipitate types that form in an Mg-rich Al-Mg-Si-Cu alloy with 0.12 wt% Ag additions, during over-aging at 200C, have been analysed by Annular Dark Field Scanning Transmission Electron Microscopy (ADF-STEM). It was found that most precipitates had lath morphology, with the long dimension along <001>Al and cross-sections along <100>Al. They have disordered crystal structures, with no unit cell present. The disorder can be explained as different arrangements of Al, Mg, Cu and Ag atoms on a common a = b ≈ 0.4 nm hexagonal network defined by Si atomic columns as viewed along the laths longest directions. The base plane of the network is aligned along the <100>Al directions. Local ordered areas consistent with the hexagonal a = b = 1.04 nm, c = 0.405 nm Q’/Q phase and monoclinic a = 1.04 nm, b = 0.81 nm, c = 0.405 nm, γ = 101° C-plate phase exist on the Si network. The Ag additions therefore do not change the precipitation sequence in the analysed Al-Mg-Si-Cu alloy. T...
With the purpose of increasing the extrudability of lean alloys, we reduce levels of the alloying elements Mg and Si in a 6xxx extrusion alloy. To avoid sacrificing strength, we investigate the compensating effect of smaller amounts of... more
With the purpose of increasing the extrudability of lean alloys, we reduce levels of the alloying elements Mg and Si in a 6xxx extrusion alloy. To avoid sacrificing strength, we investigate the compensating effect of smaller amounts of lithium and germanium, alone and in combination. Recent studies by atomically resolved high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) together with density functional theory (DFT) calculations have demonstrated that while Li replaces Mg, Ge substitutes Si in the columns in the hardening β’’-phase. Several studies have shown that Ge replaces Si in other precipitates as well, and that both Li and Ge promote precipitation and can improve macroscopic properties, like strength and thermal stability. The scope of the current work has been to investigate and document the combined effect of the two alloying elements. Of the investigated alloys, the one containing both elements displayed highest hardness, corresponding wit...
To investigate differences in precipitation coarsening upon ageing at elevated temperatures, two Al-Mg-Si-Cu alloys, one Mg-rich (A) and one Si-rich (B), with similar amount of solutes were studied by Transmission Electron Microscopy... more
To investigate differences in precipitation coarsening upon ageing at elevated temperatures, two Al-Mg-Si-Cu alloys, one Mg-rich (A) and one Si-rich (B), with similar amount of solutes were studied by Transmission Electron Microscopy during overageing at 250C. The hardness of alloy A was found to be significantly higher than for alloy B, by producing a fine precipitate microstructure. The fine particles in alloy A consisted of laths/plates extending along <001>Al, having cross-sections along <100>Al directions. The laths and plates were identified as (disordered) L-phase and C-phase respectively, both which are common precipitates in the Al-Mg-Si-Cu system. Minor transformation to the equilibrium phase Q/Q’ was observed. In contrast, alloy B developed a considerably coarser precipitate microstructure; The main phase being Q/Q’ laths extending along <001>Al, but with cross-sections oriented along <510>Al. After 100h at 250C the average cross-section area of pr...
Ruben Bjørge, Philip N.H. Nakashima, Calin D. Marioara, Sigmund J. Andersen, Barry C. Muddle, Joanne Etheridge and Randi Holmestad Department of Physics, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway ARC... more
Ruben Bjørge, Philip N.H. Nakashima, Calin D. Marioara, Sigmund J. Andersen, Barry C. Muddle, Joanne Etheridge and Randi Holmestad Department of Physics, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway ARC Centre of Excellence for Design in Light Metals and Department of Materials Engineering, Monash University, Victoria 3800, Australia Department of Synthesis and Properties, SINTEF Materials and Chemistry, 7465 Trondheim, Norway Monash Centre for Electron Microscopy and Department of Materials Engineering, Monash University, Victoria 3800, Australia
The effects of 3%–50% pre-deformation following solution heat treatment on the age hardening of an Al-3Mg-1Cu alloy have been investigated by Vickers microhardness measurement, tensile tests, differential scanning calorimetry, scanning... more
The effects of 3%–50% pre-deformation following solution heat treatment on the age hardening of an Al-3Mg-1Cu alloy have been investigated by Vickers microhardness measurement, tensile tests, differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. Pre-deformation has a strong effect on subsequent age-hardening behavior. The precipitation was accelerated, hardness peaks appeared earlier, formation of clusters was inhibited, and a larger fraction of precipitates was observed along the dislocation lines. The contribution of the precipitates to the hardness was evaluated by dissolution tests. It was found that pre-deformation followed by artificial aging resulted in a good strength-elongation balance. The results are significant for the development of combined mechanical deformation and heat treatment processes.
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ABSTRACTThe Al-Mg-Si (6xxx-series) alloy system is a precipitation hardened alloy gaining much of its strength from precipitate phases acting as pinning centers for dislocation movement. Five years ago, Zandbergen, Andersen and coworkers... more
ABSTRACTThe Al-Mg-Si (6xxx-series) alloy system is a precipitation hardened alloy gaining much of its strength from precipitate phases acting as pinning centers for dislocation movement. Five years ago, Zandbergen, Andersen and coworkers identified the crystallography of the so-called β″ phase, one of the main hardening phases, using solely electron microscopy techniques [1]. Later, several other phases have been identified using high resolution microscopy. To solve the crystallography of these phases and to get an increased understanding of the electronic structure and bonding, ab initio modeling has proven to be a valuable tool. We present results from calculations on two recently discovered phases and show how ab initio modeling can give insight into the bonding trends and electronic structure of the phases in this alloy system.
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Al-Mg-Si(-Cu) alloys are an important group of age hardening materials and possess some of the more complex precipitation sequences: In Al-Mg-Si, none of the metastable hardening precipitates can be described as weakly distorted versions... more
Al-Mg-Si(-Cu) alloys are an important group of age hardening materials and possess some of the more complex precipitation sequences: In Al-Mg-Si, none of the metastable hardening precipitates can be described as weakly distorted versions of equilibrium phases, while in Al-Mg-Si-Cu, one of the main hardening precipitates is not associated with a unit cell. For both sequences, however, more than a decade of experimental work has revealed that a Si substructure with projected hexagonal symmetry when viewed in precipitate main growth axis projection is shared among all metastable phases. The present work seeks to clarify theoretically the significance of the Si network to phase stabilization while also quantifying the level of similarities among the various phases possessing this structure. Based on these results, very clear suggestions for a common precipitate nucleation mechanism emerge.
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The metastable β″-hardening phase in aged 6xxx-series Al alloys has been investigated by three-dimensional atom-probe in order to evaluate the composition (Mg5Si6) of the structure, previously determined by high-resolution transmission... more
The metastable β″-hardening phase in aged 6xxx-series Al alloys has been investigated by three-dimensional atom-probe in order to evaluate the composition (Mg5Si6) of the structure, previously determined by high-resolution transmission electron microscopy (HRTEM) and electron diffraction. For β″, a significant number of Mg and Si atoms are found to be lost during detection in atom-probe analysis. The reason of this is non-resolved events, in which the correlation between the time-of-flight (TOF) and the detected position of the field-evaporated ion is lost. The problem is attributed to uneven evaporation and can be avoided by the use of an advanced delay-line detector (ADLD), which is capable of discriminating extremely closely spaced detection events. Preliminary analysis of a β″-particle using this detector gave a Mg/Si ratio of 0.9 and a composition of 15 at.% Al. The Al level is significantly lower than those previously measured by other atom-probe detectors, because of the higher efficiency of the ADLD in detecting Mg and Si in particles. Atom-probe analysis with the ADLD detector is consistent with the β″ Mg/Si ratio derived from electron microscopy analysis. The measurements indicate that Al atoms may substitute both Si and Mg positions. Copyright © 2007 John Wiley & Sons, Ltd.