Aluminum casting alloy with high strength, high conductivity, and heat resistance is required as the secondary conducting material for the high speed induction motor. The liquidus of Al-0.5%Zr-xSi (x=0.02-1.0 mass%) alloy were calculated by CALPHAD method, and casting temperature was decided. Effects of Si content on hardness and conductivity changes during aging at 623-723 K of Al-0.5 mass%Zr-xSi alloys cast process in iron mold were studied, and the heat resistance at 423 K for alloy with

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... mum characteristic was investigated. A small addition of Si accelerated the hardening and high conductivity of the Al-0.5 mass%Zr remarkably. The maximum hardness was obtained by aging at 673 K. Hardness and conductivity of Al-0.5%Zr-0.45%Si alloy aged at 673 K for 28.8 ks was 61.7 HB and 55 IACS%, respectively, and these characteristics in room temperature hardly changed by isothermal treatment at 423 K.