The crystal structure of the β″ phase in Al–Mg–Si alloys

Vissers, R.; Huis, Marijn A. van; Jansen, J.C.; Zandbergen, H.W.; Marioara, Calin Daniel; Andersen, Sigmund Jarle

doi:10.1016/s1359-6454(97)00493-x

Cited by 597 publications

(333 citation statements)

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“…The appearance of double-lines confirms that the precipitates are surrounded by a coherency strain field. At least 90% of the precipitates, as the one enlarged in figure 3(d), were identified as β"-precipitates having a unit cell of a=1.516 nm, b=0.405, c=0.674 nm and an angle between a and c of 105.3° [4]. By assuming that all the precipitates are β" with composition Mg5Si6, an estimate is given of the amount of Mg and Si that is left in solid solution.…”

Section: Precipitate Structure In Peak Aged (T6) Conditionmentioning

confidence: 99%

“…The clusters gradually transform into GP-zones, which are more related to the crystallography of the matrix [3], and further into β"-precipitates. β" has been established as a monoclinic Mg5Si6-phase [4], and its occurrence is often observed to coincide with the maximum strength of the alloy (T6). Upon overageing several types of particles are formed, such as B', β' and β, …”

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Precipitation, strength and work hardening of age hardened aluminium alloys

Ryen¹,

Holmedal

Marthinsen

et al. 2015

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract. The strength and work hardening of age hardened AA6063 and AA6082 alloys have been investigated in terms of a detailed characterization of precipitate and dislocation structures obtained by TEM and SEM. Tensile and compression tests were performed at as quenched, peak aged and severely aged conditions. A strong work hardening in the as quenched condition was found, similar to AlMg alloys with twice as much alloying elements in solid solution. It was found that the initial work hardening rate and the critical failure strain are both smallest at the peak aged condition. During large deformations the needle-shaped precipitates are sheared uniformly by dislocations altering their <001> orientations, which indicates extensive cross slip. In the overaged condition the early initial work hardening is larger than at the peak aged condition, but followed by a weak linear work hardening, apparently directly entering stage IV at a low strain. Cracked, needle-shaped precipitates were seen at larger strains.

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Section: Precipitate Structure In Peak Aged (T6) Conditionmentioning

confidence: 99%

mentioning

confidence: 99%

Precipitation, strength and work hardening of age hardened aluminium alloys

Ryen¹,

Holmedal

Marthinsen

et al. 2015

IOP Conf. Ser.: Mater. Sci. Eng.

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“…This phase is described by the monoclinic C2/m space group and was initially thought to have composition Mg5Si6, but Mg5Al2Si4 is probably closer to the truth [5,6]. Its lattice parameters have been measured to a = 1.516 nm, b = 0.405 nm, c = 0.674 nm, and its monoclinic angle is 105.3° [2,3]. The phase was chosen since it is one of few fully coherent phases in aluminium alloys, and the main hardening phase of an industrially important alloy system.…”

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confidence: 99%

“…In this study, we focus on measuring the misfit of perfectly coherent β'' precipitates of the Al-Mg-Si system [2][3][4] through scanning transmission electron microscopy (STEM). This phase is described by the monoclinic C2/m space group and was initially thought to have composition Mg5Si6, but Mg5Al2Si4 is probably closer to the truth [5,6].…”

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

Wenner

Holmestad

2016

Scripta Materialia

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The age-hardenable Al-Mg-Si alloy system is strengthened by needle-shaped coherent β'' phase precipitates. Using distortion-corrected high-resolution scanning transmission electron microscopy images, we measure the considerable misfit between β'' particles and the Al matrix. The β'' phase is found to adapt its lattice parameters to the particle shape, distributing the strain in the Al matrix evenly in its cross-sectional plane. The measured misfits give a good match to reported atomistic simulations for a β'' phase with composition Mg5Al2Si4.Keywords: electron microscopy, aluminium alloys, precipitation, misfit strain 2 Coherent precipitates in age hardenable alloys and the misfit strain fields they induce in the surrounding matrix have been text book material for many decades [1]. Such precipitates form by thermally activated diffusion, nucleation and growth. A precipitate particle stays coherent until it grows too large for the matrix to accommodate all its misfit. After this, precipitates experience a loss of coherency, and the strain fields diminish, weakening the material. This can happen through several mechanisms:(i) a phase transformation to a less coherent phase (ii) formation of an incoherent surface layer at the matrix-precipitate interface (iii) introduction of interface (misfit) dislocations The precipitate phase can also relieve the system of some strain before coherency loss occurs by less drastic modifications:(iv) generation of stacking faults in the precipitate phase (v) chemical adjustments, including an increased vacancy density in or outside the precipitate phase All five effects can be studied using theoretical calculations such as density functional theory (DFT) or continuum mechanics through the finite element method (FEM). However, calculations need support by experiments at the atomic scale. Experimental studies require that we can both observe the causes (e.g. a single stacking fault) and quantify the resulting change in lattice strain. It is equally important to ensure the absence of faults, if the strain around a perfectly coherent particle is of interest.In this study, we focus on measuring the misfit of perfectly coherent β'' precipitates of the Al-Mg-Si system [2-4] through scanning transmission electron microscopy (STEM). This phase is described by the monoclinic C2/m space group and was initially thought to have composition Mg5Si6, but Mg5Al2Si4 is probably closer to the truth [5,6]. Its lattice parameters have been measured to a = 1.516 nm, b = 0.405 nm, c = 0.674 nm, and its monoclinic angle is 105.3° [2,3]. The phase was chosen since it is one of few fully coherent phases in aluminium alloys, and the main hardening phase of an industrially important alloy system. It is also needle-shaped with a long main coherency direction, often extending through the TEM specimen in which it resides. The lattice strain is therefore uniform through the specimen, and can be measured reliably in a projected image of a precipitate cross-section.When corrected for spherical aberratio...

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“…[5] summarised observed phases in each kind of alloy. The proposed sequences are shown in the table 1. β" phase is coherent phase, with composition accepted to be Mg 5 Si 7 [6,9,11,13,16] [5,8,11,12]. This ambiguity may be however caused by constant migration of atoms in the elevated temperature.…”

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Influence of Age Hardening Parameters on the Microstructure and Properties of the AlSi7Mg Sand Cast Alloy / Wpływ Parametrów Utwardzania Wydzieleniowego Na Strukturę I W Łaściwości Stopu Alsi7mg

Poloczek¹,

Dybowski²,

Rodak³

et al. 2015

Archives of Metallurgy and Materials

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Aluminium alloys are characterized by a low density, acceptable mechanical properties and good technological properties. This unique connection of features made aluminium alloys perfect structural material for the transportation industry. Also, due to their good electrical conductivity they also found application in energy production industry. High mechanical properties and electrical conductivity of the Al-Si alloys with Mg addition may be achieved by heat treatment. However, the highest mechanical properties are achieved in the early stages of age hardening - due to precipitation of coherent phases, while high electrical conductivity may be achieved only by prolonged aging, during precipitation of semi-coherent or fully noncoherent, coarse phases. Carefully heat treated AlSi7Mg alloy may exhibit both fairly high electrical conductivity and slightly increased mechanical properties. The following article present results of the research of influence of heat treatment on the properties and microstructure of sand cast AlSi7Mg alloy. Microstructure observations were performed using light microscopy, scanning electron and scanning-transmission electron microscopy. Hardness and electrical conductivity of the AlSi7Mg alloy were investigated both in as-cast condition and after heat treatment. Maximum hardness of the alloy is achieved after solutioning at 540°C for 8h, followed by 72h of aging at 150°C, while maximal electrical conductivity after solutioning at 540°C for 48h, followed by 96h of aging at 180°C. Increase of the electrical conductivity is attributed to increasing distance between Si crystals and precipitation of semi coherent phases.

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The crystal structure of the β″ phase in Al–Mg–Si alloys

Cited by 597 publications

References 13 publications

Precipitation, strength and work hardening of age hardened aluminium alloys

Precipitation, strength and work hardening of age hardened aluminium alloys

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

Influence of Age Hardening Parameters on the Microstructure and Properties of the AlSi7Mg Sand Cast Alloy / Wpływ Parametrów Utwardzania Wydzieleniowego Na Strukturę I W Łaściwości Stopu Alsi7mg

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