The Life Testing Of Die-casting Mold For Aluminum Alloy Electric Shell

The aluminum alloy electric shell is the basic component of the UHV AC apparatus. And the shell castings are formed by low pressure casting. However, the die-casting mold is foremost for the production of the aluminum alloy shell. In the process of the aluminum alloy die-casting, the work conditions of mold are very complicated. The mold will be affected by thermal-cooling cycles, the corrosion and scour of aluminum alloy melt, the corrosion of die-casting coatings and so on, thus making the service life shorten. The service life of die-casting mold is one of the key indicators to measure its quality, which is related to the production efficiency and the cost of the aluminum alloy die-casting. Currently, the materials for die-casting mold are different, which are classified by the casting alloys, service condition and so on. The ductile QT500-7 has excellent comprehensive property, such as high resistances to thermal fatigue, fine cutting performance, strength and toughness, low cost. Generally speaking, QT500-7 is selected as the one of the best mold materials for the aluminum alloy die-casting. And the ductile QT500-7 is the object of this research.This paper discussed the service life of the mold for aluminum alloy die casting by the thermal fatigue testing and fatigue testing under different stress. We adopted self-restraint thermal fatigue method and tested by the homemade thermal fatigue test equipment, In order to make the test conditions similar to the actual service conditions, we heated the QT500-7 specimens by the aluminum alloy malt and cooled in the air. The testing results show that the ductile QT500-7 has strong resistances to thermal fatigue and the thermal fatigue cracks don’t appear before 5000 cycles. However, the surface of the specimen is oxidized and the oxidation corrosion pits appear under 4000 cycles. QT500-7 is easily oxidized and the oxide layer will fall off, making that the pits form and enlarge with the cycles increasing. On the other hand, we made the fatigue testing of QT500-7 under 495-315MPa. The results show that the low-cycle fatigue is different from the high-cycle fatigue and it’s worse in toughness under high stress. The fatigue limit of QT500-7 is 15MPa. To sum up, the casting mold material QT500-7 can meet the requirement service life of 10000.