발간논문

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Vol.14, No.4, 368 ~ 382, 1976
Title
Ageing Response in Dilute Al - Cu - Mg Alloys
조현기 Hyun Kee Cho
Abstract
An investigation has been carried out for the precipitation process in dilute Al-Cu-Mg alloys containing 2.0wt% Cu and 1.1wt% Mg by the observations of the transmission electron microscopy and the detailed measurement of changes in hardness and electrical resistivity during ageing at the various temperatures between 40°and 300℃. The pre-precipitation in this alloy has occured in three different ageing stages; (1) G. P. B. zones formed during quenching and ageing for less than 1 minute known as the stage of fast reaction, (2) G. P. B. zones formed in the early stage of ageing below 200℃ known as the stage of slow reaction, and (3) G. P. B. (2) zones formed in the early stage of ageing above 250℃. From the electrical resistivity measurement, the apparent activation energy for the formation of zones in the stage of slow reaction has been determined to be 0.26±0.04eV. The critical ageing temperature at which the rate of zone formation comes to maximum is found to be in the range of 70°∼120℃. The distribution of dislocation loops and loop free zone (LFZ) have been observed at such a low ageing temperature as 70℃ on prolonged ageing. The metastable S` phase has been precipitated on the dislocation lines and formed the S` composite precipitate sheets on the｛210｝planes in the <001> growth directions of the matrix. The equilibrium S phase has been precipitated at the elevated ageing temperature above200℃ on prolonged ageing.
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