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WO1999061886A1 - Caracterisation d'echantillons thixotropiques - Google Patents

Caracterisation d'echantillons thixotropiques Download PDF

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Publication number
WO1999061886A1
WO1999061886A1 PCT/GB1999/001453 GB9901453W WO9961886A1 WO 1999061886 A1 WO1999061886 A1 WO 1999061886A1 GB 9901453 W GB9901453 W GB 9901453W WO 9961886 A1 WO9961886 A1 WO 9961886A1
Authority
WO
WIPO (PCT)
Prior art keywords
specimen
load
compression
predetermined
slug
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB1999/001453
Other languages
English (en)
Inventor
Plato Kapranos
David Harvie Kirkwood
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Sheffield
Original Assignee
University of Sheffield
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University of Sheffield filed Critical University of Sheffield
Priority to EP99923732A priority Critical patent/EP1082598A1/fr
Publication of WO1999061886A1 publication Critical patent/WO1999061886A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N11/00—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G01N3/18—Performing tests at high or low temperatures

Definitions

  • the present invention is in the field of thixoforming of metals and alloys, and relates to a method of, and apparatus for, characterising specimens of such metals and alloys to enable their suitability for thixoforming to be determined, and to compare different materials and materials prepared under different conditions.
  • Semi-solid metal forming, tMxoforming, thixocasting and thixoforging are all terms applied to a relatively new technology in the forming of complex shapes of metal bodies in a mould or die.
  • a metal or alloy is given a suitable microstructure, usually by stirring during solidification or by remelting of a re-crystallised structure, but in any event, so that it comprises essentially globular, non-dendritic grains.
  • EP- A-0305375 describes one method of preparation of an alloy suitable for thixoforming.
  • a slug of the material is heated under precisely controlled conditions to around its freezing point where it comprises solid grains in a liquid matrix having a variable fraction solid, depending on the temperature.
  • the slug is allowed to soak for a period of several minutes during which the temperature and fraction solid of the slug is stabilised, and possibly during which some modification of the structure occurs, for example, further spheroidisation of the globules. After this time the slug is then rapidly injected into a die. Under high shear, the viscosity of the material in this condition rapidly dirninishes and it flows into the die in a controlled and relatively uniform manner, it having the consistency under such shear akin to thick oil.
  • the injection is characterised by an essentially smooth front of the injected material as it penetrates the die so that gas is reliably ejected from the die without entrapment.
  • detecting the load applied or the compression rate at a sampling frequency of at least 10 3 s "1 , preferably at least 2 x 10 3 s '1 ; and characterising the specimen on the basis of the change in load or compression rate, as the case may be, detected during compression.
  • the predetermined compression rate or load applied is maintained constant during compression.
  • it is the compression rate which is predetermined, and in which event it is the load applied to maintain such compression rate that is detected.
  • said characterisation comprises a peak value of load or negative peak (ie drop) in compression rate on commencement of compression of the specimen.
  • Such a method has two essential features. Firstly, the usual industrial conditions of thixoforrning are reproduced. Secondly, and equally importantly, the sampling frequency (ie rate at which measurements are made) is sufficiently high to detect the apparent peak of viscosity of a thixotropic material in the moments before its structure "yields" or “breaks down” as substantial shear is applied and at which point its viscosity rapidly reduces to the low level at which it flows. Indeed, it is the appreciation that the shape of the load/(time or compression) curve, particularly the peak (if any), is characteristic of thixotropic behaviour that the invention finds its application.
  • the suitability or otherwise of a material for tmxoforming can all be determined, or at least approximated.
  • the first aspect of the present invention also provides thixoforming material characterisation apparatus, comprising:
  • control means adapted to operate the ram at a predetermined velocity, regardless of load, or a predetermined load, regardless of velocity, to establish an average shear rate in the slug in excess of 10 s " ⁇ preferably at least 10 2 s ' more preferably at least 10 3 s "1 ;
  • a sensor to detect one of the load applied to, or compression rate experienced during compression of, the slug by the ram, the sensor being adapted to operate at a sampling frequency of at least 10 3 s '1 , preferably 2 x 10 3 s " '.
  • said control means is adapted to maintain the predeterrnined velocity or predetermined load constant during compression.
  • it is the velocity which the control means is adapted to maintain at said predetermined rate
  • said sensor is a load sensor.
  • the ram moves the first plate and the load sensor is disposed between the second plate and a fixed frame of the apparatus.
  • the plates comprise a relatively hard, thermally non-conductive material such as an asbestos, or asbestos-like, composition, for example Sindanyo. This ensures as far as possible isothermal conditions during the compression. The hardness of the material reduces any cushioning effect.
  • the second plate is mounted in an aluminium plug having tapered sides and received in a corresponding bore of the frame, the sensor being mounted between the said plug and the frame.
  • the frame extends from said bore around a slug mounted on said first plate.
  • Said first plate may be integral with the ram.
  • the tapering of the plug ensures that it lifts substantially fiictionlessly from the frame on compression of the slug by the first plate.
  • the present invention comprises a method of characterisation of a thixotropic specimen comprising the step of quantifying the breakdown point at which flow of the specimen commences.
  • the invention also comprises thixoforming material characterisation apparatus, comprising means to quantify the breakdown point at which flow of a specimen to be characterised commences.
  • the detection and quantification of this initial resistance which looked at another way may be considered as the material's yield point, in specific materials will be of value to manufacturers employing thixoforrning processes.
  • the method and apparatus of the first aspect of the invention are suitable for putting the second aspect into effect.
  • Figure 1 is a schematic view of apparatus according to the present invention
  • Figure 2 is a detailed view of a compression cell of the apparatus of Figure 1
  • Figure 3 is a plot of load or force applied (in KN) against time (in s);
  • Figure 4 is a plot of viscosity (in 10 4 Pa.s) calculated from the values of Figure 3 against calculated average shear rate (in s '1 );
  • Figure 5 is a micrograph of the microstructure of an aluminium alloy sample after rapid compression in the apparatus of the present invention.
  • a thixofoirning press 10 comprising a frame 12 having a base 14 on which an actuator 16 is disposed.
  • the actuator 16 has a ram 18 which is adapted to rise and fall and which, on its end, has a pedestal 20 on which a slug 22 of the specimen material is supported.
  • the frame supports induction heating coils 26 supplied by cables 28 from a power source 30.
  • the induction coils 26 when energised with current heat the slug 22. After the heating process (described further below), is complete, the ram is raised to introduce the slug 22 into a compression cell or die 32 held by a die clamp 34 of the frame 12.
  • Figure 2 shows the compression cell in more detail.
  • the pedestal 20 comprises a first plate made of Sindanyo which has low thermal conductivity.
  • the pedestal 20 slides in a close sliding fit in a graphite core 36 mounted in the frame 12.
  • the graphite core supports a further Sindanyo second plate 38 which is mounted in an aluminium plug 40 having tapered sides 42.
  • the plug 40 is mounted in a correspondingly shaped bore of the graphite core 36, and on its other side mounts a steel cap 44.
  • a load cell 46 is pressed between the cap 44 and a steel backing plate 48 of the frame 12.
  • the plug 40 has tapered sides so that, when the ram 20 raises the slug 22 against the plate 38, the transmission of the load to the steel plate 48 and load cell 46 is essentially instantaneous and frictionless.
  • a computer 50 controls the apparatus 10 and receives signals from the load cell 46 for subsequent processing.
  • Slug 22 comprises any metal or alloy which it is desired to characterise in relation to its rheological properties and will typically comprise an alurninium alloy or other metal/alloy. In the present embodiment, it comprises a cylindrical slug 42mm high and
  • the velocity of compression is arranged to be between 200 and 2,000mm per second, and if earned out between plates 20, 38 of low thermal conductivity and within the chamber defined by the graphite core 36, it is assumed that isothermal conditions pertain for the period of the test.
  • the ram When the temperature of the slug is at the desired level, the ram is raised and the slug 22 compressed between the plates 20,38 at the defined rate.
  • the load cell 46 is arranged to provide signals corresponding to the compressive force on the slug 22 and the computer control 50 is arranged to collect such signals at a rate of two kilohertz.
  • the measured load is plotted against time for the alloy A357 at three different temperatures, namely 572°C, 574°C and 576°C.
  • the ram was advanced at 500mm per second so that a time of 0.06 seconds represents a compression of the slug from 42mm to 12mm in height with consequent sideways expansion until contact with the core 36 and resultant rapid growth in the load when the progression of the ram 20 is stopped.
  • Curve a is at the lowest temperature, 572°C and represents a fraction solid of 0.6. At time zero the load applied rises rapidly to a peak value of approaching 4 KN before equally rapidly decreasing to a minimum of about 0.4 KN at time 0.01 seconds, whereupon the load remains substantially constant over the next 0.025 seconds before the approaching end of the test when the load rises rapidly. Thus the peak lasts for a period of less than 0.01 seconds.
  • Graph b shows the alloy at a higher temperature, 574°C and therefore a smaller fraction solid of about 0.5.
  • the load rises at the same point as for curve a, but reaches a first peak at a value of 1 KN.
  • curve c shows the alloy at a temperature of 576°C and the peak on this curve is hardly noticeable and occurs after a delay of almost 0.01 seconds.
  • the delay probably represents a slump of the slug in view of its much lower fraction solid (of about 0.4) so that there was very little resistance to compression until the end of that delay.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)

Abstract

L'invention concerne des briquettes d'échantillon thixotropiques (22) soumises à une compression isotherme en vue d'obtenir un taux de cisaillement en excès de 10 s-1, la charge requise pour maintenir la compression étant régulée à un taux de plus de 2 KHz, si bien qu'une force de pointe requise au début de la compression pour désintégrer la microstructure de l'échantillon, avant la fluidification, peut être détectée et mise en oeuvre pour caractériser l'échantillon.
PCT/GB1999/001453 1998-05-26 1999-05-26 Caracterisation d'echantillons thixotropiques Ceased WO1999061886A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP99923732A EP1082598A1 (fr) 1998-05-26 1999-05-26 Caracterisation d'echantillons thixotropiques

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9811237A GB2337822B (en) 1998-05-26 1998-05-26 Material characterisation
GB9811237.8 1998-05-26

Publications (1)

Publication Number Publication Date
WO1999061886A1 true WO1999061886A1 (fr) 1999-12-02

Family

ID=10832682

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1999/001453 Ceased WO1999061886A1 (fr) 1998-05-26 1999-05-26 Caracterisation d'echantillons thixotropiques

Country Status (3)

Country Link
EP (1) EP1082598A1 (fr)
GB (1) GB2337822B (fr)
WO (1) WO1999061886A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2802642B1 (fr) * 1999-12-17 2002-01-18 Commissariat Energie Atomique Viscosimetre et procede de mesure de viscosite
EP1136809A1 (fr) * 2000-03-22 2001-09-26 Alusuisse Technology & Management AG Détermination de la solidité d'un corp métallique préchauffé avec des propriétés thixotropiques

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1987006957A1 (fr) * 1986-05-12 1987-11-19 The University Of Sheffield Materiaux thixotropes

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3693412A (en) * 1971-03-18 1972-09-26 George L Kalousek Method for measuring thixotropy
DE2827593C3 (de) * 1978-06-23 1981-07-16 Bayer Ag, 5090 Leverkusen Verfahren zur Ermittlung rheologischer Kenngrößen von viskoelastischen Stoffen
IT1182533B (it) * 1985-07-24 1987-10-05 Cselt Centro Studi Lab Telecom Metodo e apparecchiatura per la misura del punto di rammollimento di un oggetto in materiale vetroso
FR2656373B1 (fr) * 1989-12-26 1992-04-24 Forex Neptune Sa Methode de test in situ d'un fluide de forage.
CH690252A5 (de) * 1995-04-27 2000-06-15 Buehler Ag Vorrichtung zum Bestimmen des Feststoffanteiles.

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1987006957A1 (fr) * 1986-05-12 1987-11-19 The University Of Sheffield Materiaux thixotropes

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
LAXMANAN V ET AL: "DEFORMATION OF SEMI-SOLID Sn-15 PCT Pb ALLOY", METALL TRANS A DEC 1980, vol. 11A, no. 12, December 1980 (1980-12-01), pages 1927 - 1937, XP002115919 *
LOUE W R ET AL: "Microstructure and rheology of partially remelted AlSi-alloys", 10 June 1992, PROCEEDINGS OF THE 2ND INTERNATIONAL CONFERENCE ON THE PROCESSING OF SEMI-SOLID ALLOYS AND COMPOSITES; CAMBRIDGE, MA, USA JUN 10-12 1992, WARRENDALE, PA, USA, PAGE(S) 266 - 275, XP002115920 *
SUERY M ET AL: "EFFECT OF STRAIN RATE ON DEFORMATION BEHAVIOR OF SEMI-SOLID DENDRITIC ALLOYS", METALL TRANS A OCT 1982, vol. 13A, no. 10, October 1982 (1982-10-01), pages 1809 - 1819, XP002115918 *

Also Published As

Publication number Publication date
EP1082598A1 (fr) 2001-03-14
GB9811237D0 (en) 1998-07-22
GB2337822A (en) 1999-12-01
GB2337822B (en) 2002-04-24

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