Liquid Al-75i-Mg alloy has been poured into plate-shaped cavities via four different designs of running system. The mode of filling in each of the running systems designs has been recorded on video tape (from which still frames are presented) bythe use of real-time x-ray radiography. Increasing severity of turbulence impaired the tensile strength and reliability of the cast material. The fall in reliability of the properties has been quantified by Weibull analysis. In addition, the appearanceand size of defects found within the castings was determined by the design of the running system. Severe surface turbulence was found to lead to macroporosity resembling hot tears in pure Al cast plates, and to mold erosion and consequent sand inclusionsin Al- 75i-Mg alloy cast plates.The use of ceramic foam filters in the running system were found to increase the reliability of the cast alloy, primarily through the control of the metal velocity and not the removal of inclusions from the liquid metal. In fact, preliminary evidence wasfound to suggest that, in normal foundry use, such filters do not hold back any significant numbers of inclusions, and may actually increase the number of inclusions in the casting. For aluminum alloys, where the major inclusions are oxide films, thefilter seems to shred and ravel the films to produce more compact defects, which are then dispersed throughout the casting. Such dispersed defects are shown to be associated with dispersed microporosity, and are suggested to be the cause of themicroporosity.
展开▼
