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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

a) b) Wear path x 2 200

a) b) Wear path x 2 200 2 200 µm µm 2 50 2 50 µm µm Figure 4.84 a) Microstructure and b) SEM micrograph with the EDS spot analysis of the wear path of FATOIS. 185

5. DISCUSSION First the properties of the MMCs are discussed and compared with those of the pure infiltration alloy. Properties are influenced by the preform pore structure and its chemistry. Residual porosity influences the performance and preform saturation is important and is discussed. Finally, the results of preform infiltration experiments are compared to one dimensional infiltration models. 5.1. Tailoring properties of preform MMCs The main task in composite research is to combine the desirable properties of the different phases. Even though high strength Al alloys are available for use up to a temperature of 150°C, above this point the mechanical properties reduce drastically. For MMCs consisting of an Al alloy matrix with ceramic particles and/or fibres, the target is increased elastic modulus, greater strength and wear resistance combined with sufficient failure tolerance at room and elevated temperatures combined with an economic material synthesis process. The drastic reduction is not observed in preform-based MMCs due to the interconnected phases. Kniewallner (51) demonstrated for Saffil fibre-reinforced Al alloy MMCs that, if the room temperature properties were superior to the pure alloy, the gap in properties is even larger at elevated temperatures. This behaviour was assumed to be applicable for the MMCs produced in the present research and therefore only room temperature properties were assessed. 5.1.1 Pure alloy properties The chemical and mechanical properties of the pure alloy IS (EN AC-AlSi12Fe), a commercial high pressure die casting (HPDC) alloy, are specified in EN 1706 (148) . Here the minimum mean tensile strength of HPDC materials is higher (240 MPa) than that of gravity chill cast materials (150 MPa). The latter process is closest to direct squeeze casting 186

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