Influences of Fe-impurity on the production process of SiC fiber reinforced Al for electric cables

As electrical power demands increase every year, the need becomes stronger for light weight electric cables which have high transmission capacity, hig h thermal resistance and low sag. We have developed a SiC fiber reinforced aluminum electrical cable to meet this need. Mechanical properties of the S iC/Al composite conductor are very susceptible to iron impurity which becom es mixed in the Al matrix during manufacture of the composite conductor. In this work, we studied the effects of Fe impurity in Al on fracture behavio r of the composite conductor. A preformed wire was prepared by dipping a bu ndle of 1500 pieces of SiC fiber (Si: 63.7, C: 35.8, O: 12.3 mass %) into m olten Al in which 0.36 mass % Fe and 0.5 mass % Ti were mixed. The Ti was a dded to improve the wetting property. Test samples were prepared by bundlin g seven preformed wires together. A tensile test was carried out for the co mposite conductor, and pull-out behavior of SiC fiber at the fracture surfa ce was observed by scanning electron microscopy (SEM), energy dispersive X- ray spectroscopy (EDX) and electron probe micro analysis (EPMA). Pull-out o f SiC fiber was observed at the fracture surface of the composite conductor using Fe-free Al. However, pull-out of SiC fiber was not observed at the f racture surface of the composite conductor using Fe-containing Al since Al was combined inseparably with the SiC and Fe. The fracture origin of the Fe -containing sample was a precipitated Fe-compound at the SiC/Al interface. Tensile strength of the Fe-containing sample was a half of that of the Fe-f ree sample. We propose the following the precipitation mechanism for the Fe compound. In manufacturing of the preformed wire, molten Al solidifies fro m the surface to the SiC/Al interface because of the low thermal conductivi ty of the SiC fiber. In the cooling process, Fe-free Ti-compound precipitat es in the molten Al by a peritectic reaction. This leads to a higher concen tration of Fe in the molten Al near the interface, and finally, FeAl3 compo und precipitates at the SiC/Al interface. (C) 1999 Kluwer Academic Publishe rs.