A test that determines the relative thermal fatigue resistance of mold materials for permanent mold aluminum alloys has been developed. This test has been used to test the thermal fatigue resistance of several potential mold materials. The results indicate that a relatively lower thermal fatigue resistance is obtained with gray irons. The resistance of compacted graphite and ductile irons was next, followed by the cast 4140 and H-13 die steel, with the best resistance from properly heat-treated wrought PG H-13 steel. The higher hardness materials generally produce better thermal fatigue resistance.
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