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These cooling curves indicate the effects of different levels of lanthanum when modifying A356 aluminum.


• All lanthanum additions led to the development of significant recales- cence prior to eutectic growth; no recalescence was observed in the alloy at high levels of cerium additions.


by lanthanum and cerium additions of up to 1.5% and 1%.


• Lanthanum caused modification of the eutectic silicon into a fine, fibrous silicon structure in which the modifi- cation level was observed to increase with increasing levels of lanthanum. Cerium had a moderate effect on the structure of the eutectic silicon.


This set of cooling curves describes the effects of cerium modification at several concentrations.


(e.g. wrought materials) could be cast- ing to shape and heat treated. Bruno Bourassa, Danny Jean, Alain


Lemieux, Joseph Langlais and Fred Major, Rio Tinto Alcan, Jonquiere, Canada, conducted a study examin- ing how the interrelated topics of homogenization time and temperature, iron level and cooling rate affected mechanical properties and phase


transformation in 6061 and 6082 wrought alloys. Once they had their results, they looked at ways to improve the casting of 6061 aluminum.


Conclusions • Aluminum wrought alloys in the 6000 series can be cast to shape if the chemistry and casting process are optimized to control hot tearing.


• The modification of eutectic silicon in A356-type hypoeutectic Al- Si-Mg alloys with lanthanum and cerium may be attributed to the suppression of the nucleation tem- perature of the eutectic silicon phase and to the limited growth due to the decrease in diffusion rate.


• The rare earths form mainly white, needlelike ternary phases or gray plate-like quaternary intermetallic phases when their concentration exceeds approximately 1% by weight.


Casting Vs. Wrought


In “Solidification and Heat Treat- ment of 6061 and 6082 Alloys for Use in Shape Casting,” a team of researchers set out to see if two alumi- num alloys that are typically worked mechanically to produce the desired final component shape and properties


ONLINE RESOURCE Visit www.moderncasting.com to read the papers discussed in this article.


May 2011 MODERN CASTING | 53


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