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Researchers and foundrymen examine ways to promote CMMCs.

Aluminum and magnesium cast metal matrix composites (CMMCs) offer additional applications in weight reduction for automakers as well as many other commercial and industrial applications.

However, the emerging technology of CMMCs still faces an uphill struggle in the transition from the laboratory to the commercial foundry floor.

These and other topics were discussed at the 2nd International Conference on Cast Metal Matrix Composites held October 4-6 at the University of Alabama-Tuscaloosa. The gathering provided an interface between researchers and foundrymen to increase the development and application rate of CMMCs and other industrial processes.

More than 30 presentations were made by researchers, producers and foundrymen from 11 countries.

If CMMCs are to have any realistic application outside the aerospace industries, they must be available at a competitive cost, said Gerald Cole, Ford Motor Co. Automotive applications would include such items as brake rotors, engine blocks, heads, pistons and air-conditioning system components.

Ford, which has done much testing of CMMCs, believes significant opportunities exist for their application in the automotive industry, Cole said. However, these parts must be of high quality and cost effective.

A complete understanding of the process reproducibility of CMMCs is required if product and material engineers are to specify the product.

The "time line of technology" is of critical importance in determining when these new materials find application in the automotive industry, Cole said. Since material decisions are made many years in advance and test work must be completed, the use of new materials will be delayed if engineers and designers are not confident, he added.

Near-Net Shapes

Several presentations led by William Hoover, Duralcan USA, reviewed current foundry technology for producing near-net shape CMMCs. The presentations discussed process parameters and requirements to produce quality CMMC parts.

Hoover indicated a significant commitment for the production of metal matrix composite raw material. However, standard techniques and procedures must be developed for CMMC property testing and specifying, he said.

Philippe Meyer, Montupet, explained that problems with conventional aluminum alloys include poor elevated temperature properties, wear resistance and modulus of elasticity.

Montupet is working to overcome these effects by using particulate and short fiber reinforcement preforms in specific locations in the casting. The company has had considerable success with a diesel cylinder head. Their work has led them to use |Al.sub.2~|O.sub.3~ fibers and platelets instead of SiC.

"The metallurgical bond between the preform and the conventional alloy requires special treatment," Meyer said.

Other Applications

M. Nolte, Aachen University of Technology, presented a unique investment casting application of continuous fiber preforms in an aerospace application.

The preform, produced by winding on a mandrel, allowed reinforcement in specific areas. The technique involved the impregnation of the preform with wax and then inserting the preform in the wax die for injection to make the pattern. Though conventional shell-building techniques were used, special techniques were required for good infiltration of metal in the fiber. Increases of 50% in tensile strength, 300% in modulus and 250% in fatigue properties were obtained. This technique will allow the designing of many aerospace structural castings in aluminum to replace current parts machined from solid, Nolte said. Biomimetic studies on metal matrix composites was the subject of Benlian Zhou, International Centre for Materials Physics, Academia Sinica, Shenyang, China. His paper dealt with the difficulties in design and processing that have retarded industrial application of metal matrix composites.

Zhou examined the completeness and efficiency of biomaterial. Biomaterial can be considered a composite when one looks at the fiber/matrix concept. By mimicking biomaterial's structure, composites can be improved, he said.

Examples in his experiments included "the dumb-bell model of reinforcement simulating animal bone," which improved strength by 100%; the tree root type structure, which improved not only strength but fracture toughness; and the distribution of fibers to mimic the structure of bamboo, which improved flexural strength by 81%.

Through more studies in this area, further advantages are expected in CMMCs.
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Title Annotation:2nd International Conference on Cast Metal Matrix Composites; cast metal matrix composites
Author:Rasmussen, Wayne M.
Publication:Modern Casting
Date:Jan 1, 1994
Previous Article:Process control: tensile testing.
Next Article:Updating diecasting technology.

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