Page 322 - Biaxial Multiaxial Fatigue and Fracture

306 El LINO ET AL.

All the parts were pressure diecasted in the AS9U3 (NF A57-703) [SI aluminium alloy. The
typical microstructure of this alloy consists essentially in ct aluminium dendrites, aluminium-
silicon eutectic cells, and intermetallics A12Cu, A1,CuzFe and AlFeSiMg [6, 111 (see Fig. 3).
Table 1 presents the alloy chemical composition specified by the Standard NF A57-703 and the
medium values measured in the components using a spark spectrometer. This table shows that
there are no significant differences between the two compositions.

Fig. 3. Typical microstructure of the pressure diecasting AS9U3 alloy (etched with HF 0.5%).
This microstructure is composed by a aluminium dendrites, aluminium-silicon eutectic cells,
and intermetallics A12Cu, A1,CuzFe and AIFeSiMg.

Table 1. Chemical composition (%) of the aluminium alloy AS9U3 (NF A57-703) [SI.

__
Fe Si Cu Zn Mg Mn Ni Pb Sn Ti
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NFA57-703 1.3 7.5-10 2.5-4.0 A-1.2 0.3 0.5 0.5 0.2 0.2 0.2
B-1.3
Measured in 0.78 9.24 2.99 0.81 0.2 0.23 0.05 0.15 0.04 0.02

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Figure 4 presents the cross section of an optical micrograph showing interdendritic (region
A) and gas cavities (region B) regions, and also a macrograph of a transversal section of an
unacceptable pedal, where these defects can also be observed. As one can see, pressure
diecastings present a significant amount of micropores. This fact is responsible for considerable
research in the foundry area, in order to produce aluminium diecastings with better
characteristics [l, 5, 13-15].