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2 µm - eTheses Repository - University of Birmingham

2 µm - eTheses Repository - University of Birmingham

The microstructure after

The microstructure after heat treatment of the AlSi-TiO2-MMC shown in Figure 4.63 a) was similar to that resulting from the same preform infiltrated with the Al-Mg alloy IM. The investigations of the different phases are presented in 4.8.12. (a) TOPC10IS (b) MOPC20IS Figure 4.63 Microstructure of reactive MMCs after thermal analysis test. a) TOPC10IS and b) MOPC20IS. In the micrograph of MOPC20IS in Figure 4.63 b), the amount of the Si phase in the intergranular coarse metal ligament areas was reduced significantly when compared with the micrograph prior to the SDTA cycle in Figure 4.55 c). The amount of the mid-grey phase in the intragranular region was increased. An EDX investigation confirmed the mid-grey phase to be pure Si from the alloy. Therefore, as already indicated by the differential thermal analysis, no reaction product was formed during the SDTA cycle of the MMC sample. 4.8.10 Infiltration behaviour with Al-Mg alloy IM The infiltration alloy was changed from an Al-Si alloy (IS) to an Al-Mg alloy (IM) with an equivalent molar fraction of the main alloying element (Mg) as listed in Table 3.2. The influence of probable reactions on the infiltration behaviour of the reactive preforms TOPC10, MOPC20 and FATO was studied and the threshold pressure P0 and the gradient of the infiltration curves were evaluated through linear regression. 161

Infiltration depth L² L² (mm²) /mm² 35 30 25 20 15 10 5 TOPC10 MOPC20 FATO 0 0 1 2 Pressure Pressure Pmet P/ MPa (MPa) met 3 4 Figure 4.64 Square of infiltration depth as a function of the applied pressure infiltration with Al-Mg alloy IM. Linear regression in the range of 2 mm to 5 mm infiltration depth except FATO in the range of 2 mm to 4 mm. In the same manner as presented in Figure 4.48 when infiltrating with the alloy IS, the square of the infiltration depth of the preforms is presented as a function of the applied pressure in Figure 4.64. Good linear fits were found for MOPC20IS and TOPC10IS. In contrast, the infiltration of FATO exhibited unsteady behaviour above an infiltration depth of 4 mm. Therefore the linear fit was limited to the infiltration depth below this point. Table 4.6 Results of infiltration curve regression analysis when infiltrating with Al-Mg alloy IM. Gradient, a, and threshold pressure of infiltration, P0. a P 0 (at L²=0) mm² / MPa MPa TOPC10 19.77 2.31 MOPC20 21.58 1.05 FATO 50.92 1.35 Table 4.6 summarizes the threshold pressures P0 for the three materials infiltrated. The gradient of the fitted line of TOPC10 was similar to that of MOPC20, whereas that of FATO was more than double. 162

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