Factors Influencing Deformation Behavior and Electrical Conductivity of Pure Copper Castings Fabricated by Industrial Process

Abstract

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.

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

“…Figure 1 shows the casting design, where a sand mold with two-piece cavities was employed. 5,6) The sand mold was made from silica sand and water glass by the CO 2 process. Plates of spheroidal graphite cast iron (room temperature) were used as chills.…”

“…Here the uniform elongation refers to elongation at the maximum stress, which is a practically important tensile property because some cracks may occur after the maximum stress. 5,6) The solid line in Fig. 3(a) indicates the minimum tensile strength (155 MPa) of an industrial standard for electrical pure copper castings, JIS H 5120 CAC102.…”

“…6) Both the rupture elongation measurement according to JIS and a direct comparison with the minimum of CAC102 are difficult tensile specimens (unit: mm). 5,6) specimens. Therefore, the requisite uniform elongation was used as an alternative standard in this study.…”

“…5) In addition, the castings with the CuCu 2 O eutectic phase exhibited higher electrical conductivity than those without the phase. 5,6) However, the presence of the eutectic phase likely makes pure copper castings brittle. 5) To ensure both high electrical conductivity and ductility of pure copper castings, the new casting process must be improved to make to impart pure copper containing the eutectic phase with sufficient ductility.…”

“…Through the aforementioned investigation, we also found that the differences in crystal grain morphology and/or hydrogen behavior due to differences in the cooling conditions during the solidification process affect the ductility of the pure copper castings. 5,6) In the present study, to clarify these effects, we prepared pure copper castings under several solidification conditions, where various degrees of superheat were employed and some conditions included chills, whereas others did not, and subsequently conducted tensile tests using the castings. On the basis of the results, we propose a casting method that can stably provide ductile pure copper castings for electrical parts.…”