Processing of Single Crystal Aluminum Using Compacted Alumina Powder




This experiment was designed to produce single crystal aluminum specimens through the understanding of solidification and processing parameter effects. In order to conduct the experiment, specimens were prepared by steel die casting and machining. After aluminum specimens were machined and ground, they were placed in the center of a crucible. Alumina powder was then filled and compacted in the crucible. The crucible was placed in a furnace for the remelting process. Finally, it was placed on a heat sink and was allowed to solidify. The powder compacting methods and remelting temperature were the two most important processing parameters. They were modified to improve the test and create single crystal microstructure. It was found that the compacting methods significantly affected the formation of leak within the crucible. Extremely dense powder  results in crack openings; extremely loose powder results in formation of branch-like leakages. Uniformly and gently compacted powder will optimize the result. Remelting temperature affects the amount of thermal expansion. High temperature results in large amount of expansion,
and causes cracks in the powder. Low temperature requires much more time and it cannot be guaranteed that the specimen is completely melted. The grain size and microstructure of each trial was compared and analyzed. Necessary modification of procedure was also made to improve future results. Finally in the report, the processing parameters and the resulting microstructure were correlated and discussed.