The influence of Ni layer covering carbon fibre on the structure of pressure die cast AlSi13Cu2/CFNi composites

Andrzej Zyska, Zbigniew Konopka, Małgorzata Łągiewka, Maciej Nadolski Politechnika Częstochowska, Katedra Odlewnictwa, al. Armii Krajowej 19, 42-200 Częstochowa, Poland

Quarterly No. 3, 2008 pages 306-311

DOI:

keywords: metal matrix composites (MMCs), carbon fibre (CF), coverings, pressure die casting, microstructure

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abstract The results of quantitative metallographic examinations concerning the arrangement of carbon fibre in AlSi13Cu2 alloy matrix composites have been presented. The HTA 5M81 carbon fibre of diameter equal to 7.5 µm and 5 mm length, covered with nickel layer (0.25 µm), produced by TENAX Company, have been used as the reinforcement. Composite castings containing 5, 10, or 15% by volume of the reinforcing phase have been examined. Composites have been produced by mechanical mixing and subsequent pressure die casting in the DMKh160 horizontal cold chamber machine. The assessment of the reinforcing phase arrangement within the silumin matrix has been done according to the structure non-uniformity index (ν). This index has been at the level of 0.120.22, what is a low value for the heterophase materials and indicates the relatively uniform distribution within the matrix volume. There has been also revealed a tendency of the structural uniformity to increase in proportion to the fibre volume fraction. It has been found that the fibre surface preparation with the Ni layer improves its wettability and facilitates the mixing process, what results in achieving a composite of isotropic structure with clearly separated and uniformly distributed reinforcing phase. Next the microstructural examination has been performed for the fibre/matrix interfacial regions, which has shown that under the conditions of composite production the Ni layer is completely dissolved and new phases of the Al3¬Ni type (containing Fe and Cu) arise. These phases occur both in the form of separated precipitates within the whole matrix volume and as locally centred around the carbon fibre. However, the exposed fibre surfaces do not undergo the degradation process due to the short time of contact with the molten AlSi alloy and the relatively low temperature of the process.