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The technical components are subjected to a great load when processing aluminum melt in a highly corrosive and oxidizing environment, and at the same time are in an environment with high temperature and large temperature fluctuations. Under these conditions, system components and additives made of oxide fiber composite materials (OFC) have a significantly higher service life than components made of traditional materials.
There is a growing demand for materials for tools and system components used to process aluminum melts to offset wear and contamination, which are no longer easily met by traditional materials. The focus of the foundry industry is increasingly turning to the development and inspection of suitable materials, the most important of which is the chemical resistance during aluminum processing and good physical material properties such as strength, ductility or thermal shock resistance melt. So-called oxide fiber reinforced oxide ceramics (or oxide fiber composite materials, OFC) represent a relatively new class of materials.
The future of foundries is aluminum
Using these OFC materials, oxide ceramic fibers are embedded in a porous oxide ceramic matrix. The specific failure mechanism of energy-dissipating microstructures leads to materials with quasi-ductility and damage resistance. Compared with unreinforced monolithic ceramics, local cracks on the components will not cause damage to the entire system. This can be demonstrated by piercing the nails through the OFC panel without cracks (Figure 1).
Figure 1: Local damage on the components does not cause damage to the entire system, which can be demonstrated by passing a nail through the OFC panel without cracks. (Source: Philipp Kolbe)
This material property also makes it possible to machine through turning, milling or drilling, which provides more choice and design freedom than traditional ceramics. Another feature is the composition of OFC material, which is mainly composed of aluminum oxide (Al2O3) without any silicon component, so it is related to aluminum melt and atmospheric oxygen, and has excellent inherent corrosion and oxidation characteristics. This proves the chemical resistance to liquid aluminum and its alloys, as well as extremely favorable wetting behavior and easy removal of solidified aluminum from OFC components (Figure 2).
Figure 2: The solidified aluminum melt from OFC material can be easily taken out of the metering container. (Source: Philipp Kolbe)
In addition, from a physical point of view, these materials are very suitable for aluminum melts. Special attention must be paid to high material strength and damage tolerance under thermomechanical loads. This good resistance to changes in thermal conditions ensures that the OFC component has a constant material strength during the aluminum melt immersion process (Figure 3), which is a significant advantage compared to non-reinforced monolithic ceramics. In addition, OFC materials stand out due to their good thermal properties. The realization of low thermal conductivity and thin wall thickness is particularly advantageous here. Compared with parts made of traditionally used materials, the material density of less than 3 g/cm³ and thin-wall design options also make lightweight engineering possible and improve operability.
Figure 3: Tensile strength of OFC sample after immersion test in AlSi9Cu3 alloy. (Source: Philipp Kolbe)
Using OFC components to process aluminum melt can significantly improve product and process characteristics. Therefore, the OFC material category has the potential to improve or replace components that process aluminum melts, which are made of metal, ceramic or graphite materials in current industrial practice.
Figure 4: In the case of metering chutes and distributor feeders, expenditures and costs can be significantly reduced. (Source: Philipp Kolbe, TU Bergakademie Freiberg)
This will bring various benefits, depending on the application case. In the case of metering launders and distributor feeders (Figure 4), it is possible to significantly reduce expenditure and cost by eliminating the sizing process and reducing energy use by avoiding overheating and reducing temperature loss due to thin walls. design. In addition, since ceramic particles will not be washed out of the launder or sizing particles, a longer service life and higher casting quality can be expected. In addition, since the risk of brittle fracture is eliminated, higher process reliability can be achieved. Therefore, the overall cost is reduced and the manufacturing process becomes more profitable.
The OFC material developed can also be used in the design of melting crucibles for aluminum melts (Figure 5). Due to the favorable wetting behavior and the chemical resistance of the material, the ingress of dirt through the crucible material is minimized. In addition, OFC materials have excellent resistance to corrosive aluminum melts and oxygen-philic and highly reactive materials (such as sodium or strontium for modification). This means that crucibles made of OFC can be used for different alloy compositions, while providing the possibility of almost complete output, because adhesion is eliminated.
Figure 5: The developed OFC material can also be used in the design of aluminum melt smelting crucibles. (Source: Philipp Kolbe)
Very good resistance to changing thermal conditions and shape stability during thermal cycling allows the use of maximum temperatures up to 1100 °C. The crucible does not have to be heated to the operating temperature, and the crucible does not become brittle or soften during permanent use. The aluminum melt can be solidified in the OFC crucible and melted again without any problems, so it has a significant improvement compared with the prior art. The thin wall thickness and thermo-mechanical properties of the material make it particularly suitable for induction furnaces. The distance between the melt and the induction coil is reduced. Compared with the most advanced methods, the material can be melted in a shorter interval, thereby saving energy. The non-damage and direct cleaning of OFC components also greatly reduces the workload of production staff. From an ergonomic point of view, lightweight engineering structure is an advantage.
With OFC components, many optimized refractory applications can be realized for aluminum foundries and their employees. The main features and advantages of innovative materials for aluminum melt processing can be summarized as follows:
The applications presented do not cover the entire product portfolio imaginable. This material category opens up new application areas and possible future component development areas, from single components and applications to composite material structures, such as inlay or reinforcement materials based on existing systems. Due to favorable thermomechanical and chemical physical properties, reduced use of energy and time, and improved process conditions, the presented OFC material is in a leading position in aluminum melt processing and helps to minimize the overall cost of the foundry .
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