A New Insight to Dynamic Oxidation of Molten Metals by the Parametric Study of Oxide/Metal/Oxide Sandwich Formation
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Copyright 2019 American Foundry Society https://doi.org/10.1007/s40962-019-00395-0
Abstract The high tendency of aluminum and magnesium to oxidation challenges the production of reliable cast parts due to the formation of double oxide film-related defects. Investigating the issue, the dynamic oxidation which occurs in the pouring step would be the main concern. To characterize the dynamically formed oxide films, the so-called oxide/metal/oxide (OMO) sandwich method is suggested. In this method, blowing two separate bubbles into the melt causes the formation of a sandwich sample consisting of two oxide films and a layer of entrapped metal between them. Shape, velocity and rising behavior of the blown bubbles play an important role in the production of oxide/ metal/oxide sandwiches. The behavior of the bubbles was investigated in two media, water and sunflower oil. The obtained results were used to determine the proper
pressures of the air blown in the melt. The casting process is simulated by computer software to ensure that the mold cavity will be filled without melt turbulence via the designed gating systems. By determining the proper values for the effective parameters in producing OMO sandwiches, the casting process was done. After the solidification processes, samples were examined via X-ray radiography to get a clear picture of the location of the bubbles. Eventually, the OMO sandwiches were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).
Introduction
defects.1 Other metals and alloys such as gray cast-iron, also suffer from oxide-related defects.4 The entrance and subsequent entrapment of the surface oxide films in the melt during the pouring step deteriorate the mechanical properties and lower the reliability of castings.5 To avoid this, it is necessary to keep the melt meniscus unchanged in the filling step and to keep the entrance velocity of the melt below the critical velocity. The optimum mechanical performance of the castings is achievable if the formation, growth, and entrapment of the oxide films are restricted.6
Metal casting is one of the most economical production processes which has been considered as one of the primary phases in the production of every individual industrial component. Although, the unrepeatability in the mechanical properties of the cast part together with intrinsic casting defects reduce the reliability of such parts and limit the use of this traditional process in the case of high-tech parts.1 To have a better understanding of the effect of melt quality and casting defects on the mechanical properties and reliability of castings, Sigworth has proposed a numerical way.2 Recent studies have shown that the presence of oxide filmsrelated defects in the final cast parts is a major factor for the scattering in the mechanical properties.1,3 Due to the high affinity of the molten aluminum and magnesium to oxidation, the quality of their castings is sensitive to the generated turbulence during the casting process. As such, melt turbulence
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