Theory of hot crack formation

Fredriksson, Hasse; Haddad-Sabzevar, M.; Hansson, Karin; Kron, J.

doi:10.1179/174328405x29276

Cited by 27 publications

(15 citation statements)

References 19 publications

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“…However, as shown in the high-resolution ESRF tomographic dataset of undeformed as-cast AA5182, the material contains a myriad of small voids and thus it would appear that void nucleation is unnecessary. While the idea of void nucleation is consistent with earlier work by Farup et al [9] and Fredriksson [10] , it is unclear what effect it has on semi-solid ductility.…”

Section: Semi-solid Failure Mechanismsupporting

confidence: 78%

“…Thus, it is clear that in the early stages, hot tearing is controlled by the formation and growth of internal voids. In a second recent study, Fredriksson et al [10] presented a thermodynamic description of hot tear nucleation. In this work, it was proposed that hot tear nucleation is enhanced by the supersaturation of vacancies since these vacancies will cluster to form voids at grain boundaries or at solid-liquid interfaces.…”

Section: Introductionmentioning

confidence: 99%

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Quantitative Assessment of Deformation-Induced Damage in a Semisolid Aluminum Alloy via X-ray Microtomography

Phillion

Lee

Maire

et al. 2008

Metall Mater Trans A

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Semi-solid tensile testing combined with x-ray micro-tomography (XMT) was used to characterize the development of internal damage as a function of strain in an aluminum-magnesium alloy, AA5182. Novel techniques were developed to allow the quantification of both the size evolution and orientation of the damage to determine mechanisms controlling the early stage growth and localization. During the initial stages of semi-solid deformation, strain was observed to be accommodated by both the growth of as-cast porosity and the detection of new damage-based voids.As the volume fraction of damage increases, the growth of voids occurs in an orientation perpendicular to the loading direction, both through expansion within the grain boundary liquid and void coalescence. The damage then localizes, causing failure.2

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Section: Semi-solid Failure Mechanismsupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Quantitative Assessment of Deformation-Induced Damage in a Semisolid Aluminum Alloy via X-ray Microtomography

Phillion

Lee

Maire

et al. 2008

Metall Mater Trans A

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“…It should be noted that pores that are frequently cited as potential hot tear nuclei can originate from gas precipitation, [8] solidification shrinkage, [8] or vacancy supersaturation. [23] Figure 3 summarizes some of the possible crack initiators.…”

Section: Outline Of Hot Tearing Mechanisms As a Base Of A New Homentioning

confidence: 99%

“…One can mention the application of the Griffith criterion for brittle fracture [51,57] and vacancy-diffusioncontrolled growth. [23] The methodology for the description of crack propagation is well developed within fracture mechanics for various situations, including those resembling hot cracking, i.e., liquid film rupture, pore coalescence, high-temperature creep, and liquid-assisted fracture. [63] It is clear that the propagation of the hot crack in the potential presence of liquid (above or below the solidus) should involve the following aspects: liquid feeding (involves permeability and, inevitably structure evolution), pore coalescence, stress transfer by solid bridges, plastic deformation and creep of solid bridges in the absence of liquid, and brittle fracture of solid bridges in the presence of liquid.…”

Section: Outline Of Hot Tearing Mechanisms As a Base Of A New Homentioning

confidence: 99%

A Quest for a New Hot Tearing Criterion

Eskin¹,

Katgerman

2007

Metall Mater Trans A

229

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Hot tearing remains a major problem of casting technology despite decades-long efforts to develop working hot tearing criteria and to implement those into casting process computer simulation. Existing models allow one to calculate the stress-strain and temperature situation in a casting (ingot, billet) and to compare those with the chosen hot tearing criterion. In most successful cases, the simulation shows the relative probability of hot tearing and the sensitivity of this probability to such process parameters as casting speed, casting dimensions, and casting recipe. None of the existing criteria, however, can give the answer on whether the hot crack will appear or not and what will be the extent of hot cracking (position, length, shape). This article outlines the requirements for a modern hot tearing model and a criterion based on this model as well as the future development of hot tearing research in terms of mechanisms of hot crack nucleation and propagation. It is suggested that the new model and criterion should take into account different mechanisms of hot tearing that are operational at different stages of solidification and be based on fracture mechanics, i.e., include the mechanisms of nucleation and propagation of a crack.

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“…The hot cracks show fractographies of dendrites or solidified liquid metal films, while the cold cracks have fractographies like that of general mechanically fractured metals. A large number of researches have been made on the hot cracks encountered in continuous casting and shape casting processes and several formation mechanisms have also been proposed, [5][6][7][8][9] while few researches can be found on the cold crack in the literature. With the progress of thinner walls and a higher dimension precision of the die castings, the problem of the cold cracks resulting from the restraints of molds, inserts or casting itself is becoming more and more obvious and the prediction technology for this defect is much desired.…”

Section: Introductionmentioning

confidence: 99%

Cold Crack Criterion for ADC12 Aluminum Alloy Die Casting

et al. 2010

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A cold crack criterion for JIS ADC12 aluminum alloy die casting is proposed. Through investigating the temperature dependence of the fracture strain of JIS ADC12 aluminum alloy die casting, it was found that the fracture strain features a turning point at a temperature, T c (we called ''critical temperature to the ductility'', about 573 K for the present composition), i.e. stays low while below T c , rises rapidly to a high level beyond T c . Focusing on this character of the fracture strain, we analyzed the equivalent plastic strain (" c ) of the castings introduced below T c in casting processes by thermal stress simulations and compared with the occurrence of cold cracks in the die casting experiments. It was found that the " c of the cracking positions in the castings exceeded, while the " c of the castings without crack were much lower than the fracture strain of JIS ADC12 aluminum alloy die casting below T c . That is to say, the occurrence of the cold crack in a die casting can be judged by comparing the " c with the fracture strain below T c . Based on this proposed criterion, it is possible to predict the appearance of the cold cracks in ADC12 die castings by thermal stress simulations.

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Theory of hot crack formation

Cited by 27 publications

References 19 publications

Quantitative Assessment of Deformation-Induced Damage in a Semisolid Aluminum Alloy via X-ray Microtomography

Quantitative Assessment of Deformation-Induced Damage in a Semisolid Aluminum Alloy via X-ray Microtomography

A Quest for a New Hot Tearing Criterion

Cold Crack Criterion for ADC12 Aluminum Alloy Die Casting

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