抄録
In this report, the age-hardening curves of two Al-Cu alloys, containig 3.5% and 3.9% of Cu respectively and quenched in three different ways, are compared. In quenching, the amount of quenching stress differs according to the method employed. This three different methods of quenching were ; i)quenched into 15°C water from 520°C, which may be written “ W.Q., ii) quenched into 15°C machine-oil, which may be written “O.Q.”, and iii) quenched directly into the water bath, kept at various constant temperatures and aged therin, which may be written “ D.Q. ”. The time-hardness curves, shown in Fig. 1∼3,demonstrate that the quenching effect of water varies greatly as its temperature changes, wheras that of oil varies only a little and that quenching into the 60∼70°C water is equivalent to quenching into machine-oil. The activation energy of the age-hardening in the case of oil-quenching is calculated in Fig. 4 and 5, by the process written in our last report(5), and the result is shown in Tab. 1. The apparent value of the activation energy becomes larger when oil-quenched, which agrees with our common knowlege. We can say, however, that the natural temperature change of the water in our room will have little effect on the calculated value of the activation energy,when we take the roughness of the calculation into consideration, because Tab. 1 demonstrates the difference between the quenching into 15° and 60°C water. The aging proceeds more rapidly at higher temperatures ; on the contrary, the speed of hardening in the case of D. Q. will be more reduced at higher temperatures owing to the decrease of quenching stress. Thus, when these two results are super imposed, the speed of hardening, in the case of D. Q., will have the maximum at a certain temperature and will be reduced at higher temperatures and at last, becomes very small at 100°C,as shown in Fig. 6.
From those results,it can be concluded that the Al-Cu alloy will harden much more slowly at room temperature,when quenched without or nearly without stress.
No difference can be detected between the streaks in the Laue photographs of the two specimens of different quenching methods ; one, quenched into water and another, into 150°C oil. Therefore, the fact that the cluster appears on the (100) plane of the aluminium lattice whether the quenching stress exists or not shows that this is required from the crystalogrpahic reasons.
