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DEFECTS IN HIGH PRESSURE CASTING PROCESSES
predict the formation of contaminant veins, ideally while the de- signs of both the product and the die can be modified. The pre-
diction of phase separation using computer flow modeling is not yet possible. The currently available computational fluid dynamic
software defines the semi-solid metal as a high viscosity fluid rather than as a true two-phase mixture. A method of modeling
two-phase flow was proposed in 1997 and efforts are currently underway to develop the proposal into a viable computer model.
2
REFERENCES
1. Keeney, M., J. Courtois, R. Evans, G. Farrior, C. Kyonka, A. Koch, K. Young, ‘‘Semisolid Metal Casting and Forging,’’ in Stefanescu, D. editor, Metals
Handbook, 9th ed., vol. 15, Casting, ASM International, Materials Park, OH,
1988, p. 327. 2. Alexandrou, A., G. Burgos, and V. Entov, ‘‘Semisolid Metal Processing: A
New Paradigm in Automotive Part Design,’’ SAE Paper Number 2000-01- 0676, Society of Automotive Engineers, Warrendale, PA, 2000.
VISIONS OF THE FUTURE
171
12
FUTURE DEVELOPMENTS IN HIGH INTEGRITY DIE
CASTING
12.1 CONTINUAL DEVELOPMENT
Driven by economics, efforts are underway to further improve several aspects of the high integrity die casting processes dis-
cussed in this text. Presented in this chapter are numerous tech- nologies related to both processing and materials currently being
researched and developed.
12.2 NEW HIGH INTEGRITY DIE CASTING PROCESS
VARIANTS
Among the high integrity die casting processes discussed in this book, semi-solid metalworking is the most costly. For this reason,
it is the subject of intense research. Thixomolding威 is among the most economical semi-solid metalworking variants since the semi-
solid metal mixture is produced on demand. This process, how- ever, is currently limited to use with magnesium casting alloys.
Research is being conducted to find a suitable barrel-and-screw material for use with aluminum casting alloys. Several investiga-
tions have failed to identify a suitable material, including a re- search project sponsored by the U.S. Department of Energy.
Regardless of the setbacks, research in this area continues.
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FUTURE DEVELOPMENTS IN DIE CASTING
Holding vessel Ceramics cover
Ceramics cover Ladle
Air Induction coil Shot sleeve
Figure 12.1 Four-step process for producing a semi-solid slurry on demand.
Courtesy of UBE Machinery, Inc.
Other direct semi-solid metalworking processes are under de- velopment for use with aluminum casting alloys. Research has
focused on developing production equipment that can convert liq- uid metal into the semi-solid slurry on demand. Ube Industries
has introduced a four-step version of the semi-solid processing method
1,2
Figure 12.1. Initially, metal is ladled into a ceramic crucible just above its melting point. The liquid metal is cooled
to a target temperature using controlled air knives. Metal temper- ature is then stabilized and the liquid metal is stirred by induction
heating. The resulting semi-solid slurry is poured into a vertical shot sleeve by turning the cup upside down to isolate oxides at
the plunger tip and injected into the die.
12.3 REFINEMENTS OF MAGNESIUM ALLOYS
Magnesium alloys have many limitations that prevent its use in many applications. Several issues must be addressed to expand
the capabilities of magnesium alloys related to corrosion resis- tance and creep.
Magnesium is very susceptible to galvanic corrosion. Fastening methods must be developed and designed that inhibit galvanic
corrosion when high integrity magnesium die castings are joined with components of a dissimilar metal. Barrier coatings are being
utilized to solve this problem in some applications.
3
However, minor scratches or porosity in currently available barrier coatings
