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Fig. 2. Half of those surveyed said they added grain refiner at the same time or after additions of magnesium and strontium, when asked “When do you add grain refiner relative to other additions?”


Other), 100% of the survey takers that use a modifier said that they use strontium. Sodium is an effective modifier at low addition rates, but fades exceptionally fast. Antimony is more widespread in European metalcasting facilities and shows little sign of fade even through re-melting, but has the effect of poisoning any additions of Sr or Na that are subsequently made. Tis makes it a tricky additive unless highly controlled. Several respondents who cast hypereutectic aluminum-silicon alloys utilize copper phosphate, but this was a small selection (1%) of respondents. Fourteen percent of respondents said that they do not perform any eutectic modification.


What eutectic modification technique do you use most often? Eutectic modifiers are available in many forms similar to


the commonly used grain refiners, and like the grain refin- ers, adding cut strontium rod is the most prevalent addition technique used by the survey takers (51%). Strontium rod is typically available as a master alloy, AlSr10, with Sr15 also available for higher addition rates per kg of rod used. Again, similar to the grain refiner the next most commonly employed method of eutectic modification is through the purchasing of ingot with eutectic modification elements added to them (21%). Unlike with grain refiners, these prac- tices appear to be independent of foundry size.


How do you test for eutectic modification effectiveness? Much of the same tests used to test the effectiveness of


46 | MODERN CASTING November 2016


grain refiners can also be used for testing eutectic modifi- cation effectiveness. Spectrographic analysis for strontium is the most widely used method in this case (56%) followed by mechanical properties testing (40%). Tis was true for all metalcasting facilities, regardless of size. Half (50%) of the larger plants surveyed are using three or more test methods to check for effective modification, compared to only 5% within smaller companies. Of the respondents using eutectic modifiers, 26% of them do not test at all for effective modification.


When do you most often perform modification relative to


other additions? Responses to this question were similarly varied to the grain


refiner relative addition question. With eutectic modifiers, 60% of respondents said they add them at the same time or before Mg and Ti additions. Figure 3 shows the complete breakdown of responses. One respondent made the comment that “our additions are relative to the end product, the casting’s process, the furnace type, and a host of other variables.”


When do you add eutectic modifiers compared to other treat-


ments (degassing/fluxing)? In the case of modifying the silicon eutectic with


respect to degassing and fluxing, the most common practice is seen to be “after degassing and fluxing”, with 50% of surveyees responding as such. Making additions


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