yond that of traditional casting alloys],” he said. “Similarly, with cast ver- sions of the alloys, once you have the near-net- shape casting, you still must heat treat to gain the elevated properties that are comparable to the wrought alloy.” Dave Weiss, Eck Industries, Mani-


Pipe Plates Bars 21


Bars Under 15 Bars 15 /2


/8 to 21 /8 /2


-in. in.


in. and Over


towoc, Wis., also is working with a research team to develop a cost effec- tive method of casting wrought alloys. Weiss would like to develop a method that can easily slide into current metal- casting process fl ows. “[Wrought aluminum] alloys typi-


cally contain very low levels of sili- con, so they have fairly wide freezing ranges,” Weiss said. “If you just allow them to freeze on their own, it is dif- fi cult to feed them. That’s why the hot tearing occurs. You can avoid those [defects] by appropriate risering and cooling rates.” Casting wrought alloys should be no


different than pouring other diffi cult-to- cast materials, Weiss said. For example, many of the principals used in the casting of 200 series aluminum can be applied to the wrought compositions. “In [200-series] aluminum casting,


typically we use aluminum chills or iron chills. [With wrought] alloys, we use copper chills, and in some cases we water-cool those chills,” Weiss said. According to Weiss, Eck also uses


more extensive risering to achieve the steeper thermal gradients that are necessary to produce the strongest cast version of the wrought material possible.


Spin City Johnson Brass has


often had customers ask for wrought alloys. They simply aren’t aware that the materials aren’t avail- able in the form of a metal casting. They just know what properties they want. So the company em-


barked on its mission to cast the alloys. Mission accomplished. Then, the company had to show the materials offered


26


Wrought Iron Specifi cations in Multiple Applications Application


Tensile Strength (lb. per sq. in.) 40,000 48,000 48,000 47,000 46,000


Yield Point (lb. per sq. in.) 24,000 27,000 28,800 25,850 23,000


comparable mechanical properties to those produced as traditional wrought alloys. Check, check. The fi nal step would be to have


the alloys cleared by manufactur- ing’s many governing bodies and standards committees. Unfortunately, the materials can’t just be passed off to customers as exact equivalents to wrought chemistries. “There is no shortcut in terms of developing the alloys,” Montes said.


“It isn’t starting


over—you borrow some things


from


the wrought mate- rials, so it is a nice starting


point. But


it only gives you the ballpark.”


Johnson Brass has succeeded in having its materials recognized in the Aluminum Asso- ciation’s Pink Sheets, but the alloys are narrowly defi ned as centrifugally cast approximations of wrought chemistries.


Elongation in 8 in. (%) 12 14 25 22 20


The developers of other types of cast- wrought alloys will have to go through similar steps to obtain recognition of their alloys. “The alloys are going to have to be fully characterized as casting alloys,” Weiss said. “What we don’t know yet is how the fatigue performance differs from the wrought to the casting and what kind of corrosion issues they might have. It depends on the applica- tion, but certainly before I would use it on something I was design- ing, I would need more information.”


Still, Weiss agrees with Shankar that the alloys could be available in cost-effec- tive, production-ready forms in two to three years. His research team has shown that in some cast aluminum equiva- lents, yield strengths in the 70 ksi range can be achieved, better than any of the traditional cast alloys.


of Johnson Brass don’t suggest quite a


The experiences as


rapid


timeline. While the company began trying to perfect its properties and gain certifi cation for its al- loys when Montes was 28, he’s now 38, and only in the last half decade has it found a way to make the proprietary alloys under- standable for customers. “After we went to the Aluminum Association four to fi ve years ago, things started happening quickly,” Montes said.


MC Online Resource


The centrifugal casting process (used here by Johnson Brass to produce the above motor housing) works well with low-fl uidity wrought alloys.


Visit www.moderncasting.com for Arvin Montes’s presenta- tion on the wrought equivalent alloys available from Johnson Brass.


MODERN CASTING / August 2010


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