172
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
12.5 METAL MATRIX COMPOSITES FOR USE WITH DIE PROCESSES
173
result in accelerated corrosion at the defective location. Research is being conducted to address this problem.
Current commercial magnesium alloys are limited to near- room-temperature applications due to decreased creep resistance
as the temperature is elevated. Some magnesium alloys containing rare earth elements are available that can operate at temperatures
as high as 150⬚C with a significant cost penalty. Past research has shown that additions of aluminum and alkaline rare earth elements
barium, strontium, and calcium in magnesium form fine precip- itates of Al
11
E
3
at grain boundaries.
4,5
These precipitates inhibit creep at elevated temperatures. Of the alkaline metals currently
researched, calcium is the least costly as well as the least dense with the lowest total ‘‘cost per atom’’ of the possible choices. With
this knowledge, several magnesium alloys containing aluminum and calcium are under development.
12.4 EMERGING ALLOYS FOR USE WITH HIGH
INTEGRITY DIE CASTING PROCESSES
Aluminum and magnesium are the dominant metals utilized in high integrity die casting. However, efforts are underway to har-
ness the economic benefits of high integrity die casting processes with nontraditional die casting alloys.
Vacuum die casting is being utilized to produce components in titanium, -titanium, titanium aluminide, nickel-based alloys,
amorphous metallic glasses, and stainless steel.
6,7
The die casting dies utilized in with these alloys are fabricated from high tem-
perature refractory metals such as tungsten or molybdenum. Prod- ucts manufactured include airfoils, fan blades, structural hardware,
golf club heads, and automotive valves. Current production quan- tities are low with limited shot sizes.
12.5 METAL MATRIX COMPOSITES FOR USE WITH
HIGH INTEGRITY DIE CASTING PROCESSES
Within the materials community, composite materials are a subject of considerable research. As a result of these efforts, discontinu-
