Microstructural evolution and tensile mechanical properties of thixoformed high performance aluminium alloys

Liu, D.; Atkinson, Helen V.; Kapranos, P.; Jirattiticharoean, W.; Jones, H.

doi:10.1016/s0921-5093(03)00528-8

Cited by 242 publications

(154 citation statements)

References 9 publications

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“…Activation energy for self-diffusion in equation (48), Viscosity at a characteristic shear strain rate c γ in equation (54), Table 5 c γ Characteristic shear strain rate in equation (54), Table 5 σ Effective stress in equation (56), Table 6 S Separation coefficient in equation (56), Table 6 β , , m K Coefficients in equation (56), Table 6 1 , cr cr ε ε…”

Section: Maxwell Time E /mentioning

confidence: 99%

“…Critical strain I and critical strain II in equation (56), Table 6 b 'Breakage ratio' in equation (58), Table 6 s A…”

Section: Maxwell Time E /mentioning

confidence: 99%

“…the 'new MIT process' [25]). The cutting edge research issues are now in developing the potential for producing high performance alloys [54][55][56][57][58][59][60] and in modelling die fill with its concomitant requirement to obtain the experimental data which can support the modelling. This review focuses on the latter two areas.…”

Section: Disadvantagesmentioning

confidence: 99%

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Modelling the Semisolid Processing of Metallic Alloys

Atkinson

2005

ChemInform

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Semi-solid processing of metallic alloys and composites utilises the thixotropic behaviour of materials with non-dendritic microstructure in the semi-solid state. The family of innovative manufacturing methods based on this behaviour has been developing over the last twenty years or so and originates from scientific work at MIT in the early 1970s. Here, a summary is given of:-routes to spheroidal microstructures; types of semi-solid processing; and advantages and disadvantages of these routes.Background rheology and mathematical theories of thixotropy are then covered as precursors to the main focus of the review on transient behaviour of semi-solid alloy slurries and computational modelling. Computational Fluid Dynamics (CFD) can be used to predict die filling. However, some of the reported work has been based on rheological data obtained in steady state experiments, where the semi-solid material has been maintained at a particular shear rate for some time. In reality, in thixoforming, the slurry undergoes a sudden increase in shear rate from rest to 100s -1 or more as it enters the die. This change takes place in less than a second. Hence, measuring the transient rheological response under rapid changes in shear rate is critical to the development of modelling of die filling and successful die design for industrial processing. The modelling can be categorised as one phase or two phase and as finite difference or finite element. Recent work by Alexandrou and co-workers and, separately Modigell and co-workers, has led to the production of maps which, respectively summarise regions of stable/unstable flow and regions of laminar/transient/turbulent fill. These maps are of great potential use for the prediction of appropriate process parameters and avoidance of defects. A novel approach to modelling by Rouff and coworkers involves micro-modelling of the 'active zone' around spheroidal particles.There is little quantitative data on the discrepancies or otherwise between die fill simulations and experimental results (usually obtained through interrupted filling).There are no direct comparisons of the capabilities of various software packages to model the filling of particular geometries accurately. In addition, the modelling depends on rheological data and this is sparse, particularly for the increasingly complex two-phase models. Direct flow visualisation can provide useful insight and avoid the effects of inertia in interrupted filling experiments.

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Section: Maxwell Time E /mentioning

confidence: 99%

“…Critical strain I and critical strain II in equation (56), Table 6 b 'Breakage ratio' in equation (58), Table 6 s A…”

Section: Maxwell Time E /mentioning

confidence: 99%

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Modelling the Semisolid Processing of Metallic Alloys

Atkinson

2005

ChemInform

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“…This 3. The solidification interval, the temperature interval between the liquidus and solidus, should not be too wide, let us say less than 130 K. This criterion originates from the finding that 2014, with a solidification interval of 131K [8], is on the limit of thixoformability [9] because of susceptibility to hot tearing. A356, which is a typical casting alloy, has a solidification interval of 71K [20].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic prediction of thixoformability in alloys based on the Al–Si–Cu and Al–Si–Cu–Mg systems

2005

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Most commercial semi-solid processing (of which thixoforming is one type) utilises the conventional casting alloys A356 and A357. There is, however, a demand to widen the range of alloys, including those with higher performance which tend to show poor characteristics for thixoforming. Thermodynamic calculation packages, such as MTDATA, provide a tool for predicting thixoformability. Here, the effects of compositional variations, in particular the effect of added copper on the thixoformability of alloy A356 and the effect of added silicon on the thixoformability of alloy 2014, have been investigated using MTDATA thermodynamic and phase equilibrium software combined with the MTAL database. Criteria for thixoformability are identified and a range of alloy compositions based on Al-Si-Cu and Al-Si-Cu-Mg evaluated in relation to these criteria. Compositions which satisfy these criteria include:-308 (Al-5.5Si-4.5Cu); 319 (Al-6Si-3.5Cu); 238 (Al-10Cu-4Si-0.3Mg); 355 (Al-5Si-1.3Cu-0.5Mg); 2014 based alloys Al-4.4Cu-0.5Mg-(4~6)Si; and a range of alloys (7.5≤Si+Cu≤9 and 1.5≤Si/Cu≤2.33) and alloys (9

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“…A number of workers have characterised material produced with a cooling slope [20][21][22], or have used such material to produce semi-solid processed components for mechanical characterisation [23].…”

Section: Inmentioning

confidence: 99%

Cooling slope casting to obtain thixotropic feedstock II: observations with A356 alloy

2008

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New Rheocasting (the NRC process) is a recently developed semisolid processing route. There are two versions of this route. In one, molten alloy is poured directly into a mould and through careful temperature control during cooling a spheroidal semisolid microstructure is achieved, before the material in the mould is upended into a shot sleeve and hence forced into a die. Alternatively, the molten alloy is poured onto a cooling slope and thence into a mould before processing. The aim of the work described in this paper, and its companion, was to develop understanding of the microstructural development during the initial stages of this process i.e. in the mould before processing and with the cooling slope/mould combination. In the previous paper, an analogue system based on aqueous ammonium chloride has been used to visualise what happens when an alloy is poured into a tilted mould with a chill wall, which acts to mimic the mould and the cooling slope in the NRC process. In this companion paper, the results for pouring A356 aluminium alloy directly into a mould, and also via a cooling slope into a mould, are presented.

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Microstructural evolution and tensile mechanical properties of thixoformed high performance aluminium alloys

Cited by 242 publications

References 9 publications

Modelling the Semisolid Processing of Metallic Alloys

Modelling the Semisolid Processing of Metallic Alloys

Thermodynamic prediction of thixoformability in alloys based on the Al–Si–Cu and Al–Si–Cu–Mg systems

Cooling slope casting to obtain thixotropic feedstock II: observations with A356 alloy

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