The so-colled anneal-hardening in the primary solid solution of Cu-Al system was investigated with particular reference to the grain size. Different results were obtained in the cases of poly-crystalline and single-crystalline states, as follows:
[(1)] In poly-crystalline sheet materials, whose chemical compositions ranged between 0.4% Al and 7.7% Al, the most effective factors on the anneal-hardening of this system were the annealing temperature and the reduction degree while the effect of Al content was of little or neglible importance. Furthermore, it was found that the increment in hardness by such treatments decreases as the grain size increases, as was apparently observed in 7.7% Al alloy samples. [(2)] Similar experiments were carried out with two single-crystalline 7% Al alloy samples having different orientations respectively. They were cut in a disk shape, deformed under compression by various cold reduction degree and subsequently subjected to anneal-hardening treatment at various temperatures. In this case, however, no increase in hardness was observed, irrespective of temperature and cold reduction degree.
According to the results above mentioned, it may be concluded that the phenomenon of anneal-hardening in this alloy system is due to some conditions characteristic to the poly-crystalline state.
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