Cu-Be系及びAl-MgZn<SUB>2</SUB>系の時効硬化曲線の形について

Abstract

In our last report, we classified age-hardening into two types; non-precipitation and precipitation. Hereafter, we shall use the word “pseudo-precipitation” instead of “non-precipitation”, in order to avoid confusion. It has been guessed as the result of our research, it is believed that all the ageing-phenomena in binary alloys may proceed in such a way as to agree with the “Austin-Rickett’s formula”;\dfracp1−p=Ktn, which is given in the case of the nucleation and growth-process in steel. The only difference between the pseudo-precipitation type and the precipitation type seems to be the difference in “n” in the above formula ; “n” is nearly unity in the case of the former and other than unity in the case of the latter. Our research has been directed toward proving whether or not this is true in every case.Here,two new cases are reported. In the case of the Cu-Be (Be 2.5%) alloys ageing below 350°C belongs to the pseudo-precipitation type and “n” is found to be nearly unity,whereas,the time-hardness curve above 350°C have quite different forms (Fig. 1, 2). The hardness-time curves near 300°C are not completely hyperbolas as in the case of the Al-Cu alloys, because both types of ageing are partially superimposed in this alloy. The activation energy of the age-hardening of the Cu-Be alloy is calculated to be 7,000 Cal/Mol. The time-hardness curves of the Al-Zn-Mg alloy below 70°C are also observed. It is already known that this alloy shows the pseudo-precipitation type hardening, below 80°C. In these cases, however, as shown in Fig. 4-8, the agreement with the Austin-Rickett’s type formula is not sufficient. The relation between in\dfracp1−p and t (t: time, p: degree of hardening), in most cases, shows nearly parallel lines, the inclinations of which (corresponding to “n”) are 0.95-1.03, i.e. are nearly unity. The fact that whether the alloys are situated on the Al-MgZn2 pseudo-binary line or not seems to have no influence on these relations. The activation energy, roughly calculated, is about the same value as that of the Al-Cu alloy in the case of the pseudo-precipitation hardening.