Ultra thin wall square JIS ZDC2 (ISO ZnAl4) die castings measuring 70 × 100mm with a thickness of 0.2mm were successfully produced by optimizing casting variables using undiluted oil-type die lubricant. The castings were observed to have less porosity at the gate side, and more at the over-flow side. The microstructure of the casting was found to become finer gradually from the gate side to the over-flow side, showing some characteristic differences from general die castings, i. e., chill zone of fine dendritic α (Zn) grains do not form near the surfaces, and much finer α (Zn) grains form at the central part of the thickness. The castings showed good mechanical properties at the gate side and central part, tensile strength of 298MPa and 314MPa, elongation of 20% and 14% respectively, but lower strength and elongation at the over-flow part. The changes of the mechanical properties can be explained by the difference in the microstructures, porosities formed in the castings and melt filling behaviors during casing.

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  In this study, effects of Ni on fluidity, formation of shrinkage, mechanical properties, and machinability were studied for bismuth lead-free copper alloy castings. The fluidity of Cu-1.5Ni-4.5Sn-6.5Zn-0.03P alloy was comparable to that of CAC406. The amount of shrinkage cavity reduced at an Ni content of 1.5mass% or higher. Mechanical properties tended to decrease with increasing content of Bi, and at a Bi content of 2.0mass% or lower, the tensile strength exceeded 195MPa and elongation was over 15%. The machinability coefficient was 80 to 90% of CAC406, which enables good machining of the castings. Addition of Ni effectively reduces the Sn concentration in the liquid ahead of the solid-liquid interface during solidification to prevent segregation of Sn and to form compounds together with Sn and P between dendrite arms. Formation of compounds reduces shrinkage cavities, and also serves as chip breakers during machining, thereby improving machinability.

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  Channel segregation behaviors of Sn-20wt%Bi alloy were studied by lateral directional solidification experiments and numerical analyses. In the experiments, ingots were made by lateral directional solidification with chiller temperatures 293K, 323K and 373K to investigate the correlation between cooling conditions and distribution of segregation spots in cross sections of the ingots. Solidification interface shapes were observed by the pour-out technique in an experiment conducted at chiller temperature 323K. Directional solidification problems were also studied at six cooling conditions ; chiller temperature 273K, 293K, 323K, 353K, 373K, and 403K, using the numerical method. The degree of segregation was evaluated quantitatively by TV (Total Variation) of Bi segregation ratio. There was a little variation in spot number and TV at lower chiller temperatures. However, both spot number and TV increased at higher chiller temperatures. Moreover, the degree of segregation increased significantly when the chiller temperature became higher than a specific temperature. The lower part of the solidification interface was observed to protrude out at the beginning of solidification due to temperature drop there caused by thermal convection. Subsequently, solidification interface formed into an over-hang shape with the retardation of solidification at the bottom liquid region. Numerical analyses showed that the retardation of solidification was caused by Bi concentration at the bottom liquid region.

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