Gerald S. Cole

METAL-MATRIX COMPOSITES IN THE AUTOMOTIVE INDUSTRY : OPPORTUNITIES AND CHALLENGES

Metal-matrix composites offer considerable promise to help automotive engineers meet the challenges of current and future demands for recyclable, fuel-efficient, safe, and low-emission vehicles. These materials can be engineered to match the design requirements of automotive power-train or chassis components. Technological and infrastructural barriers tend to limit the implementation of these materials, but it is believed these barriers can be overcome and that metal-matrix composites can be applied in high-volume vehicle production. Reducing these barriers will require much effort by engineers and scientists, managers and planners at automotive manufacturers, and their suppliers. The result will be the gradual introduction of metal-matrix composites in high-volume vehicle production to satisfy customer desires while meeting regulatory requirements and competitive pressures.

Experimental observations of dendritic growth

A new technique has been developed which allows independent control of the temperature gradient and growth velocity during unidirectional solidification. This technique employs a heat source and sink which remain stationary with the solid-liquid interface as a crystal is translated to allow freezing. When the method is applied to the growth of simple binary Pb-Sb alloys, it is found that the term “dendrite spacing” does not uniquely describe our observations; and we observe that the primaries and secondaries respond differently to variations in the temperature gradient, growth velocity and concentration. The observations are discussed in terms of previous measurement of dendrite arm spacings.

Magnesium technology 2002, part I: Primary production, environmental issues, high-temperature alloys

ConclusionIt is expected that the research in high-temperature alloy development will reach a critical mass in about five years. This will not only raise the materials science of magnesium to a higher level but will also increase the confidence of the industry in magnesium as a structural performance material. Currently, applications are being actively pursued in United States Council for Automotive Research power train programs and European Council for Automotive R&D engine block programs to develop the technology for elevated-temperature magnesium. More research is still needed in this interesting materials field.

A practical method for identifying inoculants

The macrostructure of an ingot can be altered by controlling the fluid flow during solidification. Such control produces drastically different results depending on whether a solute addition acts as an inoculating agent (involving a low proportion of a nucleating second phase) or if it is mostly soluble and forms a second phase only as a result of microsegregation. This differentiation, previously shown for Al and some of its alloys, is repeated with magnesium containing zirconium, which is a known inoculant for Mg. Copper is then tested as an addition to lead. Its action allows the production of very curious macroscopic grain structures which will be shown to be characteristic of an inoculant. Subsequent tests support the validity of applying fluid flow structure-control as a method for identifying inoculants.

A transparent model for simulation of ingot front solidification

ConclusionObservations of the macroscopic freezing front in water and solutions of water with ammonium chloride reveal anisotropies identical in nature to those noted in metallic alloys. The variables which govern the anisotropies are similar for both types of materials, a fact which allows us to confirm our conclusions already stated about metals. The observations made with water are also direct ones and not inferential as must be the case for metals; we are therefore surer about other effects connected with this phenomenon of anisotropic growth. For example, cracking of the ice was often observed when the anisotropy occurred but was absent otherwise; it then appears that cracking in some metals may owe its origins to the effect of interface front anisotropy.