Abstract
Coupled studies by experimental and numerical simulations are necessary for an increased understanding of the material behaviour as related to the interaction between the thermal and mechanical conditions. This paper focus on the mechanisms of thermal fatigue in the failure of dies and cores used in the die casting of aluminum alloys. The thermal fatigue resistance is expressed by two crack parameters which are the average maximum crack and the average cracked area. Samples of various types of H13 steel were compared with a standard H13 steel by testing under identical thermal fatigue cycles. To determine the thermal constraint developed in the sample during the test, a finite difference technique was used to obtain the temperature distribution, based on temperature measurements at the boundaries. The resulting stresses and strains were computed, and the strain calculated at the edge or weakest point of the sample was used to correlate the number of cycles to crack initiation. As the strain at the edge increased, the number of cycles to failure decreased. The influence of various factors on thermal fatigue behavior was studied including austenitizing temperature, surface condition, stress relieving, casting, vacuum melting, and resulfurization. The thermal fatigue resistance improved as the austenitizing temperature increased from 1750 to 2050oF.
Highlights
Die soldering is the result of an interface reaction between molten aluminium and the die material during the impact of the high velocity molten aluminium onto the die surface and the intimate contact between alloy and die at high temperature
Once molten aluminum gets into the die with high motion, it destroys the protective film on the die surface, it reaches the primal die surface
The adhesion of the cast metal to the die surface or core is recognized as soldering,which happens by different changing reactions along with the solidification phase, because of the dependence on die layer and the aluminum alloy
Summary
Die soldering is the result of an interface reaction between molten aluminium and the die material during the impact of the high velocity molten aluminium onto the die surface and the intimate contact between alloy and die at high temperature. A compound of residual, thermal and mechanical stresses create the crack [6,7,8] This kind of failure is attributed to the inherent resistance of the die material against the brittle fracture termed fracture toughness. A majority of the studies involve the alternating immersion of samples in water and molten aluminium[26, 27] This kind of experiment is like the actual high-pressure die-casting process, though it lacks repeatability. This is attributed to the sticking feature of the molten aluminum on the sample during testing which makes it the main weakness. This problem and the surface treatment will be addressed
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