Effect of Solidification Conditions on the Deformation Behavior of Pure Copper Castings

The effect of solidification conditions on the tensile deformation behavior of pure copper castings for electrical parts was investigated. Two main types of tensile deformation properties were distinguished on the basis of the difference in uniform elongation. For the castings fabricated under a superheat of 100 degrees C or 150 degrees C, larger and smaller uniform elongation types corresponded to the absence and presence, respectively, of the Cu-Cu2O eutectic phase in the microstructure. Meanwhile, for the castings fabricated under a superheat of 50 degrees C, greater uniform elongation was sometimes obtained when the eutectic phase was present. In addition, irrespective of the presence or absence of the eutectic phase, greater uniform elongation was always obtained when chills were used. Cross-sectional observations showed the existence of considerable nonspherical porosity when the eutectic phase was present; the porosity was reduced when the pouring was conducted under the superheat of 50 degrees C and when the chills were used because of lower hydrogen content in the melt and supersaturation of the hydrogen by rapid cooling, respectively. These results suggest that not only the presence of the eutectic phase but also the inferior casting soundness due to the existence of the porosity is a dominant factor responsible for the decrease in the uniform elongation. The findings presented here indicate that a decrease in the hydrogen content in the melt and/or the rapid cooling during solidification are effective measures to stably achieve practically sufficient deformation properties along with superior casting soundness.