Papers by Author: Merton C. Flemings

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Authors: J. Wannasin, R. Andy Martinez, Merton C. Flemings
Abstract: Various processing methods exist for applying agitation to a molten metal during solidification to obtain metal slurries suitable for semi-solid metal processing. . In this paper, a new technique to achieve semi-solid metal structure using agitation during solidification is reported. The technique applies a new medium and means to efficiently create semi-solid metal structures. The results of a systematic study showing the feasibility and the necessary conditions to achieve the structure are discussed.
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Authors: J. Wannasin, S. Junudom, T. Rattanochaikul, Merton C. Flemings
Abstract: A simple and efficient rheocasting process that has recently been invented is being developed for aluminum die casting applications. The process called Gas Induced Semi-Solid (GISS) utilizes the combination of local rapid heat extraction and agitation achieved by the injection of fine gas bubbles through a graphite diffuser to create semi-solid slurry. In the GISS process, the die casting machine and the process cycle remain little changed from those of conventional die casting. The GISS unit creates a low solid fraction of semi-solid slurry in the ladle during the ladle transfer to the shot sleeve. The semi-solid slurry is then poured directly into the shot sleeve. This paper presents the detailed description of the process. The results of the semi-solid die casting experiments with ADC10 alloy using the GISS process are also reported and discussed.
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Authors: Merton C. Flemings, R. Andy Martinez
Abstract: The essential first step in semi-solid forming is to obtain a high grain density during the initial stages of solidification of an alloy melt. This is usually done by a combination of cooling and convection. If the grain density is too low, the resulting structure is one of conventional coarse dendrites, unsuitable for semi-solid forming. At higher grain densities, fine dendrites grow that can be coarsened to a spheroidal structure in a short enough time to be of practical interest for semi-solid forming. If the initial grain density is still higher, the grains grow in a fully spheroidal manner. Thus there are two distinctly different paths to formation of the desired structure: 1) coarsening of fine dendrites, and 2) direct spheroidal growth. We are beginning to understand quantitatively the conditions necessary to form spheroids in these two different ways.
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