Effects of Fe-Impurity in Al on Fracture Behavior of the Composite Conductor Using SiC Fiber Reinforced Al for Next Generation

摘要

Demand of electric power is increasing every year, and light weight electric cable is strongly needed which has high transmission capacity, high thermal resistance and low sag. Tokyo Electric Power Co., Chubu Electric Power Co. and Hitchi Cable Ltd. are breaking new ground in the field of electric cable by developing the SiC fiber reinforced aluminum conductor. Mechanical properties of the SiC/Al composite conductor is very susceptible to iron(Fe) impurity which is mixed in Al matrix during the manufacturing of the composite conductor. In this work, effects of Fe-impurity in Al matrix on fracture behavior of the composite conductor is studied.So called preformed wire was prepared by dipping a bundle of 1500 pieces of SiC fiber (Si:63.7, C:35.8, O:12.3 mass%) into the molten Al in which 0.36 mass% of Fe and 0.5 mass% of Ti were mixed. Where, Ti was mixed in Al to improve wetting property with SiC fibers. Testing samples for this study were prepared by making bundles of 7 pieces of preformed wires. Tensile test for the composite conductor was carried out, and pull-out behavior of SiC fiber at the fracture surface was observed by SEM, EDX and EPMA methods.Because SiC and Fe contained Al combined inseparably with each other, the pull-out of SiC fiber was not observed at the fracture surface of the composite conductor using Fe contained Al, which the pull-out of SiC fiber was observed in the Fe-free sample. The fracture origin of the Fe contained sample was the precipitated Fe-compound at the SiC/Al interface. Tensile strength of the Fe contained sample was a half of that of the Fe free sample. We believe that precipitation mechanism of Fe is as follows. During the manufacturing of the preformed wire, molten Al solidifies from the surface to the SiC/Al interface because of low thermal conductivity of the SiC fiber. In the cooling process, Fe free Ti-compound precipitates in the molten Al by peritecu'c reaction. As a rsults, the concentration of Fe in the molten Al near the interface becomes higher, and finally Fe-compound precipitates at the SiC/Al interface.