Case Western Reserve
University has a long record of die materials testing
and evaluation done in close coordination with the NADCA
Die Materials Committee. At the core of this activity is
the Immersion Thermal Fatigue Tester that simulates the
conditions encountered by the die material during die
casting of aluminum alloys. The effect of composition
and heat treating on the thermal fatigue resistance of
die steels has been investigated. The results of these
studies have been used to develop industry wide
specifications for die steels such as the Ford
Specification and have contributed to extending the life
of die casting dies.
The thermal fatigue test has been employed successfully
by Case Western Reserve University for over twenty five
years to evaluate a large number of potential die
materials for aluminum die casting dies. The sample is
processed to the dimensions shown in Figure 1. It is a 2
x 2 x 7 inch rectangular parallepiped specimen with a
1.5 inch diameter hole in the center for internal water
cooling. The four comers have a constant 0.010 inch
radius that intensifies the predominately uniaxial
stress at this location. The test produces considerable
constraint and high thermal fluctuations during
immersion and removal from the aluminum 380 alloy bath.
The experimental set-up is illustrated in Figure 2 and
the resulting thermal fluctuations at the specimen
comers in Figure 3. The molten bath is maintained at
1350oF and the specimen is immersed for 12 seconds and
then removed from the bath for 24 seconds to produce the
thermal cycle shown above. The outer surface of the
specimen is sprayed with a commercial water-base
lubricant just before it enters the molten aluminum
bath. Water flows through the central hole at a constant
rate of four gallons per minute. The standard procedure
is to operate the equipment for 5,000 immersion cycles,
measure the cracking pattern and follow this method for
10,000 and 15,000 total cycles. A three inches long
center section along the corners, equidistant from each
end, is used to measure the cracks at 100X. The crack
length is categorized and recorded in 50 micron
intervals. The cracking pattern is reported as the
average maximum crack length and the summation of the
squares of the crack length for each of the four comers.
The more severe the crack pattern, the lower the thermal
fatigue resistance of the tested material. The results
of this test have correlated closely with the behavior
of dies in industry.
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