6 research outputs found
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Development of Cost-Effective Low-Permeability Ceramic and Refractory Components for Aluminum Melting and Casting
The primary goal of this project was to develop and validate new classes of cost-effective low-permeability ceramic and refractory components for handling molten aluminum in both melting and casting environments. Three approaches were employed with partial to full success to achieve this goal: (1) Develop materials and methods for sealing surface porosity in thermal-shock-resistant ceramic refractories; (2) Develop new ceramic coatings for extreme service in molten aluminum operations, with particular emphasis on coatings based on highly stable oxide phases; and (3) Develop new monolithic refractories designed for lower-permeability applications using controlled porosity gradients and particle size distributions. The results of the research work and the field tests performed utilizing these three approaches are listed below: (1) It was demonstrated that high-density IR heating could be a tool for altering and sealing the surface porosity of fused silica. However, the process was not very cost-effective. (2) A low-cost glaze composition having a coefficient of thermal expansion (CTE) similar to that of a DFS tube was identified and was successfully tested for its integrity and adherence to DFS. Although the glaze acted as a barrier between the molten aluminum and the DFS, persistent porosity and crazing within the glaze affected its performance during the reactivity tests, thus acting as an obstacle in scaling up production of this glaze. (3) Pyrotek's XL glaze showed great success in improving the life of the DFS tubes. Pyrotek has reported an increasing market demand for the XL-coated DFS tubes, which exhibit useful lifetimes three times better than those of uncoated tubes. (4) A computer model to optimize particle size distribution for reduced permeability was developed and successfully applied to casting formulations. Silica riser tubes produced using these new formulations have been tested in a commercial aluminum casting facility and have been reported to increase the life of the DFS tubes by 700%. (5) If all the DFS riser tubes used in LPD casting of aluminum automotive components are replaced with the better, longer-lasting castable riser tubes, the potential national energy savings is estimated to be 206 billion Btu/year
Effect of heating rate on recrystallization of twin roll cast aluminum
Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science, 39A(1): pp. 165-170.The effect of heating rate on precipitation and recrystallization behavior in twin roll cast (TRC)
AA3105 has been investigated by three different means: conventional air furnace, controlled
infrared, and lead bath heating. Experimental results showed that as-recrystallized grain size
decreased and became more equiaxed as the annealing heating rate increased. These results were
explained via time-temperature-transformation (TTT) curves for both dispersoid precipitation
and recrystallization. With the faster heating rate, recrystallization could occur before precipitation
of Mn present in the unhomogenized TRC samples. At a heating rate of 50 degree C/s the
material underwent grain growth after recrystallization at 500 degree C. No sign of grain growth was
observed in materials annealed with lower heating rates, 3 degrees C/s, 0.5 degree C/s, and 0.01 degree C/s due to
greater dispersoid precipitation