Shoichi Danjo, Takemi Isomatsu, Ryosuke Matsuo, Masaru Higuchi


The influence of the amounts of cobalt (Co) on the strengths, the electrical conductivities, the grain sizes and the bending workability of Cu-Co-Si alloys were studied. When the amount of Co is increased, the strength after an aging treatment increases. However, the problem was that the bending workability was deteriorating by the coarsening of the grain sizes of the recrystallization structures because high temperatures are required to dissolve Co and silicon (Si) completely in the solution heat treatments, which is a former process. We have succeeded in achieving both a high strength and a good bending workability by adding a slight amount of chromium (Cr). The mechanism is that a ternary compound of Co-Si-Cr was precipitated on the grain boundary by adding a slight amount of Cr, thereby restraining a coarsening of the grain size.

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