抄録
Age-Hardening Processes can be divided, into two types: nonprecipitation and precipitation. In the former type, no precipitation, except Guinier-Preston Aggregates, may be observed until the hardness attains its maximum, while in the latter, precipitations may be detected from the early stages of the hardening pro_??_esses. Aging of the Al-Cu, Cu-Be systeme etc. in the lower temperature belong to the former and that of the Ag-Cu, Fe-Mo, systerne etc. belong to the latter. While the hardness-time curves of the Al-Cu alloy at the temperature between 0 and 70°C can be treated simply as hyperbolas with sufficient accuracy, that of precipitation type cannot be treated so. Let us define the degree of hardening as p=(H-H0)/(Hs-H0), where Hs, is the saturated hardness, H0 is the as-quenched hardness and H is the bardness at the time t, measured with Vickers or Brinell Hardness number. Then, the linear relation between 1/(1-p) and t can be realized in the case of the Al-Cu alloy at the temperature noted above and the velcsity constant of age-hardening K can be obtained from the inclivation of this line. Therefore, the activation energy of the age-hardening can be calculated from the linear relation between log K and 1/T, where T is the absolute temperature. In general, Austin-Rickett's formula (in the case of the decomposition of Austenite in steel) 1/(1-p)=Ktn+1 can be applied to both types of age-hardening, where n is nearly unity in the case of Al-Cu alloy, and is larger than unity in the case of the precipitation-type. We could deduce the Austin-Rickett's formula, in the case of age-hardening, from a few simple assumptions. We have found that the activation energy E of the age-hardening of Al-Cu alloy decreases as the concentration of Cu in the alloy decreases. The double peaks in the hardening curvei of Al-Cu alloy at high temperatures can be accounted for as follows; the first peak corresponds to the saturated hardeness of non-precipitation-hardening and the second corresponds to the maximum hardness as the result of the three-dementional growth of the aggregates.
