Factors influencing the tensile deformation behavior of pure copper castings for electrical parts were investigated. Two main types of tensile deformation behaviors were distinguished on the basis of the difference in the rupture elongation. These did not depend on the melting conditions and/or the casting design. For the deformation type with higher rupture elongation, approximately the same tensile strengths were obtained with dimpled ductile fracture surfaces. On the other hand, lower rupture elongation was always obtained for the castings fabricated without deoxidation treatment. For deformations of the lower rupture elongation type, brittle fracture surfaces with the solidification structure containing Cu Cu 2 O eutectic phase were observed. Therefore, the presence or absence of the Cu Cu 2 O eutectic phase was considered to be the dominant factor influencing the tensile deformation behaviors. These findings indicate that adequate deoxidation treatment is particularly important for the prevention of crack generation during deformation.

Al 5) AlN Al Al 7) SQ Squeeze Quenching 5 8) SQ Al AlN [ 30 p. 345-353 (2012)]

The factors influencing the tensile deformation behavior and the electrical conductivity of pure copper castings fabricated by an industrial process were investigated. The pure copper castings had sufficient deformation characteristics and electrical conductivity on the practical side. However, the deformation characteristics and the electrical conductivity of the castings were slightly inferior to those of the castings fabricated by laboratory experiments. The oxygen content in the castings fabricated by the industrial process was less than 0.01 mass％ , which resulted in the absence of Cu-Cu 2 O eutectic phase that exhibits the brittle behavior. On the other hand, observations of the fracture surface and the cross-section of the castings showed the existences of microporosity and two types of inclusions. These may be the factors influencing the decrease in the both tensile strength and uniform elongation. The microporosity were suggested to be caused by higher hydrogen content in the melt and/or by slower cooling rate during solidification. EDX analyses suggested that the inclusions are a kind of slag and straw ashes. Furthermore, phosphorus and iron content in the castings fabricated by the industrial process were higher than those in the castings fabricated by the laboratory experiments. These may be the factors influencing the decrease in electrical conductivity. The above findings indicated the several methods to improve the properties of the castings fabricated by the industrial process.

The directional solidi cation characteristics and generation patterns of isolated pools of liquid metal in plate castings with as cast holes were numerically examined, and fundamental concepts for the casting design, including the holes, were also investigated. For the as cast hole effects H/T (H: as cast hole effective range, T: plate thickness), there were differences depending on the hole size as well as the casting and mold materials, which re ect the directional solidi cation characteristics associated with the cooling effects due to the hole. For the nite-width plate castings with as cast holes, isolated liquid pools occurred at locations between a hole and an end face or between the holes under speci c conditions. The generation status of isolated liquid pools indicated that the conditions with larger values of the difference between the end and as cast hole effects (E−H)/T (E: end-effective range) in the range of 1.8-5.3 are preferable for preventing the generation of isolated liquid pools. Therefore, the consideration of (E−H)/T is useful for the casting design. In addition, the generation of isolated liquid pools could be prevented by the appropriate use of chills. Moreover, the generation was sometimes prevented by a temperature decrease of the melt during mold lling. The success of these techniques in preventing shrinkage defects was experimentally con rmed.