“They already do thixocasting [of
wrought chemistries] commercially,” said Sumanth Shankar, a professor at McMaster Univ. who has done extensive work on casting wrought alloys. “But it is very expensive. Some automotive guys make really high integrity castings [that way], but they pay a premium.” The goal now is to come up with
new ways to cast wrought materials so they can compete on the open market in applications that require properties not available with cast alloys (Table 1).
The Economics of Change Several sets of researchers cur-
rently are working to make cast- wrought alloys a prudent purchase for casting designers, and each is developing a different means to achieving that end. Diran Apelian, a professor at the
Worcester Polytechnic Institute, has developed what’s known as the Controlled Diffusion Solidification method of casting wrought chem- istries. The process plays off the traditional types of wrought casting in which semisolid material is used to overcome the high melting points, unique solidification curves and lack of fluidity of wrought materials. According to Apelian, the method
he and his team have found suc- cessful is to begin with two types of material—one investment casting- type cavity of iron powder with very low carbon content, and one crucible of molten iron with a high carbon content (roughly 4.3%). With both materials heated to the same temperature, the team then pours the molten material into the heated powder, which melts not due to heat flow but due to carbon diffusion from areas with higher carbon content to areas of lower carbon content. “It’s like brining a chicken,” Apelian
said. “It diffuses in. But as soon as the carbon leaves the liquid metal, it so- lidifies, so you have a casting through diffusion not through heat flow.” A former student of Apelian, Shan-
kar believes the Controlled Diffusion Solidification of casting wrought alloys could be commercially available in two to three years. The researchers have cast several viable samples of 2000, 6000 and 7000 series wrought alloys; all that’s left is to optimize the process
36 Metal Casting Design anD PurChasing sePteMber/OCtOber 2010
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