Development of a New Hot-cracking Test for Aluminium Alloys

Warrington, D. H.; McCartney, D.G.

doi:10.1080/09534962.1989.11818994

Cited by 64 publications

(41 citation statements)

References 5 publications

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“…[9] and [12]). In a first step, it is assumed that the deformation rate is homogeneous over the entire length of the mushy zone, i.e., that in Eq.…”

Section: Resultsmentioning

confidence: 99%

“…[13] is due to Kurz and Fisher: [1] [1] Combining Eqs. [1] and [12] allows one, then, to obtain the maximum deformation rate ( p,max ) that can be sustained ⅐ ε by the mushy zone before a hot tear nucleates at the root of the dendrites,…”

Section: Hot-tearing Modelmentioning

confidence: 99%

“…[2][3][4][5] The formation of hot tears is also linked to a lack of feeding in the mushy zone, but only for specific regions where the dendritic network is submitted to shear or tensile stresses. [2,[6][7][8][9][10][11][12][13][14] thermal contraction upon cooling. When the dendritic network is coherent,* it can sustain and, as a matter of fact, *Coherency of the dendritic network is related to the links between the fragments of solid.…”

Section: Introductionmentioning

confidence: 99%

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A new hot-tearing criterion

Rappaz

Drezet

Gremaud

1999

Metall Mater Trans A

813

506

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A new criterion for the appearance of hot tears in metallic alloys is proposed. Based upon a mass balance performed over the liquid and solid phases, it accounts for the tensile deformation of the solid skeleton perpendicular to the growing dendrites and for the induced interdendritic liquid feeding. This model introduces a critical deformation rate ( p,max ) beyond which cavitation, i.e., nucleation ⅐ ε of a first void, occurs. As should be expected, this critical value is an increasing function of the thermal gradient and permeability and a decreasing function of the viscosity. The shrinkage contribution, which is also included in the model, is shown to be of the same order of magnitude as that associated with the tensile deformation of the solid skeleton. A hot-cracking sensitivity (HCS) index is then defined as . When applied to a variable-concentration aluminum-copper alloy, this HCS ⅐Ϫ1 ε p,max criterion can reproduce the typical ''⌳ curves'' previously deduced by Clyne and Davies on a phenomenological basis. The calculated values are in fairly good agreement with those obtained experimentally by Spittle and Cushway for a non-grain-refined alloy. A comparison of this criterion to hot cracks observed in ring-mold solidification tests indicates cavitation depression of a few kilo Pascal and tensile stresses in the coherent mushy zone of a few mega Pascal. These values are discussed in terms of those obtained by other means (coherency measurement, microporosity observation, and simulation). Even though this HCS criterion is based only upon the appearance of a first void and not on its propagation, it sets up for the first time a physically sound basis for the study of hot-crack formation.

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“…[9] and [12]). In a first step, it is assumed that the deformation rate is homogeneous over the entire length of the mushy zone, i.e., that in Eq.…”

Section: Resultsmentioning

confidence: 99%

Section: Hot-tearing Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A new hot-tearing criterion

Rappaz

Drezet

Gremaud

1999

Metall Mater Trans A

813

506

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“…It is usually admitted that the use of Al-Si alloy as a filler wire decreases the hot tearing susceptibility of a weld. Numerous studies have confirmed that, as the Si content increases, the hot tearing susceptibility increases until the maximum solubility of Si in Al is reached, and then decreases rapidly [29][30][31]. Our results show that the influence of the Si content on the hot tearing susceptibility is not that straightforward.…”

Section: Application To Weldingmentioning

confidence: 50%

Non-isothermal tensile tests during solidification of Al–Mg–Si–Cu alloys: Mechanical properties in relation to the phenomenon of hot tearing

et al. 2006

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An original set-up has been used to study the mechanical properties of aluminium alloys in tension during solidification with a high cooling rate (70 K s À1 ). The mechanical behaviour of 6056 aluminium alloy with and without grain refiner has been investigated as well as that of mixtures between AA6056 and AA4047. The results show that the alloys exhibit a viscoplastic behaviour in the mushy state. A transition is observed between fracture in the mushy state and fracture in the solid state as a function of the displacement rate. This displacement rate at the transition depends on the cooling rate and on the composition of the alloy. The displacement before fracture is observed to be independent of displacement rate but to depend on the composition and on the solidification rate. Based on the observations a criterion for fracture in the mushy state is proposed. A simple rheological law describing the mechanical behaviour of the alloys is coupled to a finite element calculation giving the thermal field during the tensile test. This simulation is able to reproduce the mechanical response of the solidifying alloy during a non-isothermal test.

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“…As the alloy starts to solidify around the core, it experiences hoop and axial thermally-induced stresses and depending on the conditions of casting, bot tears might develop near the inner tube. Warrington and McCartney [5] have recently designed a new test, known now as the cold finger test. The principle of the test is to solidify an alloy around a water cooled copper chili in the form of a cone.…”

Section: Introductionmentioning

confidence: 99%

Validation of a new hot tearing criterion using the ring mould test

Drezet

1999

J. Phys. IV France

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Abstract. Hot tear is one of the most serious defect which a casting can suffer. It represents a major limitation to the production of foundry cast parts and to the productivity of continuous casting processes such as the direct chiil casting of aluminium alloys. As an exemple, the starting phase of the direct chili casting process remains particularly critical for some aluminium alloys because of their high propensity to develop either hot tears which initiate at non zero liquid fraction, or coid cracks which nucleate and grow exclusively in the solid metal. In order to validate a new hot tearing criterion recently proposed by Rappaz and Drezet [1), instrumented ring mould tests were carried out with aluminium alloys of different composition and further on analysed from a thermal, mechanical and microstructural point of view. The thermal field obtained in the test was determined with the help of an inverse method using five temperature histories measured at different locations and the stress build-up was computed with a transient thermomechanical model implemented in the finite element package Abaqus. Deformation in the solid was assumed to obey a viscoplastic law and the cooling conditions were those deduced by the inverse method. The new hot tearing criterion [1] based on the ability of the interdendritic flow of liquid to compensate for the thermally induced deformation of the roots of columnar dendrites, allowed the calculation of the maximum strain rate that the roots of the dendrites can undergo without initiation and/or propagation of hot tears. After implementation in the numerical FEM model of the ring mould test, the hot tearing criterion predicted the occurrence of tears precisely in the region where hot cracks were observed after the test. More generally, when implemented in thermomechanical models of casting processes, the present hot tearing criterion would be very helpful in diminishing the cracking tendency.

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Development of a New Hot-cracking Test for Aluminium Alloys

Cited by 64 publications

References 5 publications

A new hot-tearing criterion

A new hot-tearing criterion

Non-isothermal tensile tests during solidification of Al–Mg–Si–Cu alloys: Mechanical properties in relation to the phenomenon of hot tearing

Validation of a new hot tearing criterion using the ring mould test

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