Abstract
The properties of copper in its solid state are strongly affected by the crystallization conditions of the liquid material. ETP grade copper (Electrolytic Tough Pitch Copper) contains oxygen, which causes Cu2O oxide to crystallize in the interdendritic spaces during solidification process which due to the shape of continuous casting mould and the feed of liquid copper during the crystallization process in strand casting might cause a high risk of macrosegregation of oxygen in the copper structure. In the current paper the implied interactions of the dendritic structure of the copper strand in terms of homogeneity at the cross-section of its electrical, mechanical and plastic properties determined based on the samples taken parallelly and perpendicularly to the surface of the dendritic boundaries were analysed. The obtained results were confronted with scanning electron microscopy (SEM) images of the fractures formed during uniaxial tensile test. It has been observed that when the crystallites were arranged perpendicularly to the tensile direction the yield strength (YS) was lower and the fractures were brittle. On the other hand, when the crystallites were arranged parallelly to the tensile direction the fractures were plastic and elongated necking was observed along with the higher YS and total elongation values. The differences in values vary in terms of the applied direction of the tensile force. A characteristic positioning of the Cu2O oxide particles inside the fracture depending on the crystallite alignment and the direction of the applied tensile force has been observed.
Highlights
The mechanical properties such as ultimate tensile strength (UTS) and yield strength (YS) of the material depend on its structure, which may be controlled throughout the technological processes
Characteristic is the distribution of oxide, which form lines of discrete division of structure elements or large clusters at the junction of several division of structure elements or large clusters at the junction of several elements, which are flat images of spatially formed discrete clusters of oxide monocrystals and filling elements, which are flat images of spatially formed discrete clusters of oxide monocrystals and filling intracrystalline spaces/voids
As a result of the conducted research concerning microstructure analysis, chemical composition analysis, mechanical and electrical properties tests it was found that a discrete distribution of Cu2 O
Summary
The mechanical properties such as ultimate tensile strength (UTS) and YS of the material depend on its structure, which may be controlled throughout the technological processes. Appropriate control of the material structure is much more difficult when the processes is conducted continuously such as strand casting process of copper intended for direct processing into wire rod designated for electrical purposes (Cu-ETP). During crystallization of copper with low oxygen content the structure of the casted material contains of copper and eutectics located at the grain boundaries, and during the solidification of the strand Cu2 O oxide segregates into interdendritic spaces [16,17]. The identification of the initial size of the oxide will allow to analyse its evolution in further plastic working processes including but not limited to hot rolling (wire rod manufacturing) and wire drawing process of ETP grade copper The latter being a cold working process is characterized with significant level of strengthening of copper matrix and high unit pressure value on the wall of the die approach angle
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