Completed Research Projects
An Energy Savings Model for Heat Treatment of Casting
Advisors:
Y. Rong, R.D. Sisson, Jr., Dr. J. Kang
Students:
Y. Bai, M. Fontecchio
Description:
The solidification of most commercial alloys involves significant volume contraction. In long freezing range alloys, melt must be fed through a partially solidified, coherent dendritic network, if porosity and surface defects in the casting are to be avoided. Commercially pure metals, influenced by a temperature gradient ahead of the interface, solidify as a plane front or a short columnar zone. In this case, melt can easily feed the solidification shrinkage. However, as alloying elements are added, the freezing range increases and dendritic solidification begins to occur throughout a large portion of the casting. During the initial period of mold filling, the dendritic network remains incomplete and the melt flows with the bulk properties of a liquid. As solidification progresses, the melt flows with the properties of a suspension of growing particles (equiaxed dendrites plus any other primary phases) in a liquid. Feedability becomes important once the semi-rigid network of the dendritic grains has formed. The dendrite arms continue to coarsen through various ripening mechanisms, and the interdendritic regions decrease in size as the volume fraction of solid increases. Channels between the dendrites and grains continue to narrow, creating an increasingly tortuous path through which the remaining liquid must flow. These narrowing fluid paths may become blocked by suspensions of non-metallic inclusions or growing intermetallic particles within the melt stream. This in turn tends to make fluid flow even more difficult. Flow eventually ceases through the narrowing channels. It is during these latter stages of restricted interdendritic fluid flow that the effect of alloy composition on viscosity and surface tension become most evident.
The main objective of this project is to investigate the effect of alloying elements that are common in aluminum-silicon casting alloys on the feeding characteristics of these alloys.
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