2007 年 48 巻 4 号 p. 799-806
The substitution of Ca for a part or all of Pb in Cu-Sn-Zn alloys of 88-8-4 type was carried out in order to decrease solidification defects. The relation between cooling rate and segregation of alloying elements or solidification defects was investigated using steps shaped ingots. Finer dendrite structure was obtained due to decrease in the diffusion coefficient and mass transfer of Sn or Zn in the Cu-liquid for Ca addition alloys. The concentration of Ca and the amount of the micro shrinkage cavity in each step was almost constant in Ca added alloys. The same segregation course in the solidification path showed in both 88-8-4-Pb (CAC402) and 88-8-4-Pb-Ca alloys. In Ca added alloys, the enrichment of Sn in the residual liquid and decrease in final solidification temperature were suppressed by expenditure of Sn due to formation of the compounds consisting of Sn and Ca at higher temperatures compared with the melting point of Pb, which resulted in the decrease of the micro shrinkage cavity. Hardness of Ca containing alloys was higher than that of Ca free alloys. The tensile properties were improved by addition of 0.25 mass% Ca, because of the decrease in micro shrinkage.
