CMMCs: Past, Present & Future.

"Composites are old hats for today's foundrymen," stated P.K. Rohatgi, Univ. of Wisconsin-Milwaukee, in his Silver Anniversary Lecture titled, "Cast Metal Matrix Composites (CMMCs): Past, Present & Future (01-133)." According to Rohatgi, Inco introduced aluminum-graphite CMMCs in 1965 and so began the development process.

In his lecture, Rohatgi provided the audience with a status report of CMMCs and current applications, while also discussing future casting opportunities. This lecture was an update of his presentation in 1976 that discussed the state of CMMCs after its first 11 years.

While looking at the past, Rohatgi reminded the audience that aluminum-silicon alloys are a type of composite, as silicon is in the matrix reinforcing the aluminum. "The same can be said of ductile iron as graphite is in the matrix reinforcing the iron," he said. These composites are after the same increases in mechanical properties, and the principles are still the same, he said.

In discussing current production, Rohatgi commended Eck Industries as a leader in the production of CMMCs. He stressed that for a foundry to begin to produce these castings, it would have to reevaluate its production procedures because CMMCs require that traditional casting processes be modified. For example, an interrupted pour may be required during production to ensure defect-free castings.

While beginning his discussion of the future, Rohatgi asked the question, "Why use composites?" The answer he provided was that the specific modulus of CMMCs is greater than gray and ductile iron and titanium the material has a high wear resistance; and the material has low coefficents of expansion and friction.

"The properties you can achieve in composites can not be achieved in monolithic castings," he said. "CMMCs are being used in areas to eliminate mechanical and thermal distortion."

Rohatgi stated that the total shipment of CMMCS was 2.5 million kg in 1999. He forecasted that this will reach 5 million kg by 2004. The areas of growth for CMMCs will be aerospace, automotive (driveshafts and brake rotors), aeropropulsion, aerostructures, thermal management and recreation (bicycle frames). Rohatgi pointed to two areas of prime importance to the future of CMMC production. The first was the development of low-cost composites. Although the cost of the material has been reduced from $10,000/lb when it was introduced to $2/lb today, further reduction remains necessary.

Rohatgi discussed the research currently underway for using waste fly ash as a reinforcement. Another area for growth, he said, is copper alloy-graphite composites to replace lead in potable water applications.

Rohatgi challenged the foundry industry by stating that "further research must be performed in CMMCs so it can move forward and become a readily-used material in this new century." His list of recommended research areas included:

* techniques for recycling MMCs;

* thin-section CMMCs;

* developing simulation software for CMMCs;

* CMMC machining, including drilling and tapping;

* developing the use of low-cost reinforcements such as fly ash.