Some Finite Difference Methods for Solution of Heat Conduction Problems

Katgerman

2010

Metall Mater Trans A

Cold cracking is a potentially catastrophic phenomenon in direct chill (DC) casting of 7xxx series aluminum alloys that leads to safety hazards and loss of production. The relatively low thermal conductivity and wide solidification temperature range in these alloys results in accumulation of residual thermal stress under nonuniform cooling conditions of the billets. In addition, such alloys show a severe loss in ductility below a critical temperature of 573 K (300°C). This brittleness along with high stress concentration at the tips of voids and microcracks can lead to catastrophic failure. Casting process parameters affect the magnitude and distribution of stresses in the billet and increase the susceptibility of the material to cold cracking. In order to investigate the effect of casting process parameters such as casting speed, billet size, and water flow rate, thermomechanical simulations were applied using ALSIM5 casting simulation software. Among the studied casting process parameters, the increased billet size and high casting speed resulted in the most dramatic increase in residual stress level. Critical crack sizes that led to catastrophic failure were also calculated and are reported against process parameters.

Section: Model Setupmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Cold Cracking Development in AA7050 Direct Chill–Cast Billets under Various Casting Conditions

Katgerman

2010

Metall Mater Trans A

“…A detailed description of the models involved can be found elsewhere [23][24][25][26]. The simulated geometry consisted of the hot top, mold, water jet, bottom block and the casting domain as shown in Fig.…”

Section: Computer Simulation Processmentioning

confidence: 99%

Cold cracking in DC-cast high strength aluminum alloy ingots: An intrinsic problem intensified by casting process parameters

Materials Science and Engineering: A

Ruvalcaba

et al. 2011

a b s t r a c tFor almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DCcast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur.

“…The description of the model can be found elsewhere [11][12][13][14]. Geometry of the setup consisted of hot top, mould, water jet, bottom block, and the cast domain.…”

Section: Presentation Of the Modelmentioning

confidence: 99%

“…As mentioned in the previous section, ALSIM5 was used for the computation of temperature profile and stress/strain fields in the round AA7050 billet. The description of the model can be found elsewhere [11][12][13][14]. Geometry of the setup consisted of hot top, mould, water jet, bottom block, and the cast domain.…”

Section: Presentation Of the Modelmentioning

confidence: 99%

Numerical Simulation of Residual Thermal Stresses in AA7050 Alloy during DC-Casting Using ALSIM5

Katgerman

2010

AMR

Abstract. Non-homogenous cooling rates and solidification conditions during DC-casting of high strength aluminum alloys result in the formation and accumulation of residual thermal stresses with different signs and magnitudes in different locations of the billet. Rapid propagation of microcracks in the presence of thermal stresses can lead to catastrophic failure in the solid state, which is called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine ascast properties. Simulation of residual thermal stresses of an AA7050 alloy during DC-casting by means of ALSIM5 showed that in the steady-state conditions large compressive stresses formed near the surface of the billet in the circumferential direction. Stresses changed sign on moving towards the centre of the billet and became tensile with high magnitudes in radial and transverse directions, which made the alloy prone to hot and cold cracking.