Thermodynamic predictions of wrought alloy compositions amenable to semi-solid processing

Camacho, A.; Atkinson, Helen V.; Kapranos, P.; Argent, B.B.

doi:10.1016/s1359-6454(03)00040-5

Cited by 74 publications

(58 citation statements)

References 13 publications

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“…Previous work has shown that around 628 • C from DSC data there is around 48% liquid formed and that the main phases present, in very small quantities are Mg 2 Si, Al 13 Fe 4 and Al 6 Mn [16,26]. The resulting near spheroidal non-dendritic microstructures exhibit thixotropic properties, i.e., the material behaves like a solid if left undisturbed but flows like a liquid when under shear.…”

Section: Post Welding Heat Treatmentmentioning

confidence: 97%

A Microstructural Evaluation of Friction Stir Welded 7075 Aluminum Rolled Plate Heat Treated to the Semi-Solid State

Chegeni

Kapranos

2018

Metals

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Two rolled plates of 7075 aluminum alloy were used as starting material. The plates were welded using a simultaneous double-sided friction stir welding (FSW) process. One way of obtaining feedstock materials for Semi-solid processing or thixoforming is via deformation routes followed by partial melting in the semi-solid state. As both the base plate materials and the friction weld area have undergone extensive deformation specimens were subjected to a post welding heat-treatment in the semi-solid range at a temperature of 628 • C, for 3 min in order to observe the induced microstructural changes. A comparison between the microstructural evolution and mechanical properties of friction stir welded plates was performed before and after the heat-treatment in the Base Metal (BM), the Heat Affected Zone (HAZ), the Thermomechanically Affected Zone (TMAZ) and the Nugget Zone (NZ) using optical microscopy, Scanning Electron microscopy (SEM) and Vickers hardness tests. The results revealed that an extremely fine-grained structure, obtained in the NZ after FSW, resulted in a rise of hardness from the BM to the NZ. Furthermore, post welding heat-treatment in the semi-solid state gave rise to a consistent morphology throughout the material which was similar to microstructures obtained by the thixoforming process. Moreover, a drop of hardness was observed after heat treatment in all regions as compared to that in the welded microstructure.

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Section: Post Welding Heat Treatmentmentioning

confidence: 97%

A Microstructural Evaluation of Friction Stir Welded 7075 Aluminum Rolled Plate Heat Treated to the Semi-Solid State

Chegeni

Kapranos

2018

Metals

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“…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%

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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“…Knowledge of this point therefore allows a better understanding of material behaviour and determination of a suitable temperature for processing. Optimum fraction solids for thixoforging have been noted to be within the range of 0.3 to 0.5 [22,23]. Delaying DCP to a lower temperature and higher fraction solid, by utilisation of a lower cooling rate, has the advantage of extending the temperature and fraction solid range over which the semi-solid material can be processed [17].…”

Section: Effect Of Cooling Rate On Solidificationmentioning

confidence: 99%

Thermal Profiles and Fraction Solid of Aluminium 7075 at Different Cooling Rate Conditions

Ahmad

Naher

Brabazon

2013

KEM

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Abstracts:In order to determine suitable processing conditions for semi-solid aluminium 7075 thermal analysis (TA) was performed in order to obtain the relationship between fraction solid and temperature. During experimental work, the alloy was heated to 750°C by resistance heated box furnace and solidified at various cooling rates. Cooling curves for the metal were recorded with two thermocouples, one at the centre of the melt volume and one beside the containing crucible wall. A specially designed chamber with kaowool blanket was used to achieve the slowest cooling rate. The faster cooling rate was achieved with the crucible in open atmosphere with a set air flow rate over the crucible. A Data Acquisition (DAQ) system controlled by LabVIEW software was used to record the temperature-time profiles. From these cooling curves, the phase change at any corresponding time and temperature was estimated. The temperature difference between centre and wall of crucible was used to determine dendritic coherency point (DCP). Results show that, the slowest cooling rate with the kaowool blanket was at 0.03°C/s. An intermediate cooling rate of 0.21°C/s was achieved by leaving the melt to cool without kaowool blanket or forced air flow, and the fastest cooling rate was 0.43°C/s. The change in cooling rate altered the temperatures at which phase changes occurred, including those for eutectic and solidus. It was found that for lower the cooling rates that the DCP occurred at lower temperatures. The DCP for the cooling rate of 0.03°C/s was found to be 574°C (corresponding to 0.85 fraction solid) whereas the DCP for 0.43°C/s was found to be 623°C (corresponding to 0.55 fraction solid).

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Thermodynamic predictions of wrought alloy compositions amenable to semi-solid processing

Cited by 74 publications

References 13 publications

A Microstructural Evaluation of Friction Stir Welded 7075 Aluminum Rolled Plate Heat Treated to the Semi-Solid State

A Microstructural Evaluation of Friction Stir Welded 7075 Aluminum Rolled Plate Heat Treated to the Semi-Solid State

Modelling the Semisolid Processing of Metallic Alloys

Thermal Profiles and Fraction Solid of Aluminium 7075 at Different Cooling Rate Conditions

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