Tomisaburo Nara and Yoshito Yamada
The tensile properties and microscopic structures were investigated with copper wires prepared from zone-refined ingot by 16 passes through the molten zones, by drawing of 99% reduction. The results obtained were as follows: (1) Large recrystallized grains were observed in the refined portions aged at room temperature, but no recrystallization was observed in the impurity-concentrated portions, crude copper, and commercial vacuum-melted copper. (2) According to the progress of recrystallization, remarkable reductions in ultimate tensile strength and micro-Vickers hardness values were also observed in the refined specimens aged at room temperature; these reductions are in clear relations with the decrease in the impurity content resulting from zone melting. (3) It has been found that the half-annealing time of the most refined specimen was much shorter than that of OFHC and almost similar to that of the spectroscopically pure copper (99.999%). Accordingly, the measurement of half annealing time may be one of the valuable methods to estimate the purity of copper.
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