Considerable evidence exists, which suggests that the local pressurization of risers - in particular, blind risers - is likely to have an important effect on the reduction of dispersed porosity (microporosity) in long-freezing range aluminum alloys. In terms of the popular Niyama criterion, often used in connection with the modeling of feeding systems, it appears that a reduction of the critical values employed in conjunction with such studies will be possible. The subsequent effects upon static and dynamic properties remain to be systematically investigated as a function of the pressurization level concerned. At least three possibilities also exist, whereby the pressurization may be brought about. It is expected that further experiments using these techniques will shortly be underway.
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