Lec9

Lec.9
Possible Applications of Metal Matrix Composites
Light alloy composite materials have, in automotive engineering, a high application potential in the engine area (oscillating construction units: valve train, piston rod, piston and piston pin; covers: cylinder head, crankshaft main bearing; engine block: part-strengthened cylinder blocks), see Table 1.9. An example of the successful use of aluminum composite materials within this range is the partially short fiber reinforced aluminum alloy piston in Fig. 1.59, in which the recess range is strengthened by Al2O3 short fibers. Comparable construction unit characteristics are attainable only with the application of powder metallurgical aluminum alloys or when using heavy iron pistons. The reason for the application of composite materials is, as already described, the improved high temperature properties. Potential applications are in the area of undercarriages, e.g. transverse control arms and particle-strengthened brake disks, which can be also applied in the area of rail mounted vehicles, e.g. for undergrounds and railway (ICE), see Fig. 1.60. In the following some potential construction units made out of aluminum matrix composite materials with data concerning materials, processing and development targets are presented.
Fig. 1.59 Partial short fiber reinforced Fig. 1.60 Cast brake disk particle of Fig. 1.61 Drive shaft particle of reinforced
light metal diesel pistons [13, 14]. reinforced aluminum for the ICE 2 [64]. aluminum for passenger cars of [65].

Aluminum Diesel Piston with Fiber Reinforced Combustion Bowl
The demand for improved performance of turbo-charged diesel engines, for better utilization of fuel and smaller pollutant emissions puts conventional aluminum piston alloys to the limits of their material strength, particularly in the combustion bowl rim area (Fig. 1.59). Conventional cast aluminum alloys are limited in their application to temperatures below 350 °C, whilst the use of cast iron to cover higher temperatures means a drastic weight increase. Selective reinforcement of the critical area in the combustion bowl with ceramic fibers, here the addition of 20 vol% Saffil, doubles the hot strength and fatigue strength at elevated temperatures. Such pistons have been successfully used in commercial vehicles for a long time in series quantities of several hundred thousand pieces per year.


Fig. 1.62 Vented passenger car brake disk Fig. 1.64 Disk brake calliper for passenger cars of conventional
of particle reinforced aluminum [65]. cast iron (left) and an aluminum matrix composite material
(AMC) with Nextel® ceramic fiber 610 [67].


Fig. 1.63 Longitudinal bracing beam (Stringer) of particle reinforced aluminum [66].

Recycling
Of special economic and ecological interest for newly developed materials is the necessity for recirculation of arrears, cycle scrap and other material from these composites into the material cycle. Since ceramic materials usually occur in the form of particles, short fibers or continuous fibers for the reinforcement of metallic materials, a material separation of the components with the goal being the reuse of the matrix alloy and the reinforcement is almost impossible. However, with conventional melting treatments in remelting factories the matrix alloy can be recycled without problems.
In melting or powder metallurgically manufactured discontinuous short fiber or particle-strengthened light alloys reuse of the composite materials from cycle scrap or splinters can be possible under certain conditions. Particularly for particle strengthened aluminum cast alloys the use of cycle scrap is possible, however splinters on direct remelting cause difficulties due contamination problems.