Copper base alloy, and cast ingot and parts to be contacted with liquid

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(57) Abstract; A copper base alloy which comprises, in wt %, 2.8 to 5.0 % of Sn, 0.4 to 3.0 % of Bi, more than 0 and not more than 0.35 % of Se and is characterized in that it has improved mechanical properties while securing a specified degree of machinability and the soundness of a cast product using the alloy; a cast ingot produced by the use of the alloy; and parts to be contacted with a liquid which are manufactured by forming the alloy. The copper alloy contains decreased amounts of rare elements (Bi, Se and the like) being alternative elements for Pb, allowing the reduction of its production cost, and also exhibits mechanical properties comparable with or superior to those of a conventional bronze alloy (CAC406) available on the market while securing the machinability comparable with that of the CAC406. The above have been achieved by a correct perspective for true properties of the rare elements (Bi, Se and the like) being alternative elements for Pb and by the suppression of the occurrence of structural defects through the elucidation of the effect on the soundness of a cast product of the decrease of the alternative elements for Pb.