2.0wt%의 Cu와 1.1wt%의 Mg을 包含하는 Al-Cu-Mg 系低濃度合金의 時效析出過程을 40°∼300℃ 間의 廣範圍한 溫度區域內에서 各種時間동안 時效處理한후 硬度 및 電氣低抗測定과 透過電子顯微鏡組織觀察等의 實驗手段에 의하여 細密히 硏究한 결과는 다음과 같았다. 本合金에 있어서의 pre-precipitation은 서로다른 3곳의 時效段r階에서 일어 났었다. 그것은 fast reation stage 인 急冷 및 1分 以下의 時效段階에서 형성되는 G.P.B. zones과 200℃ 이하의 slow reaction stage의 時效段階에서 형성되는 G. P. B. zones 및 250℃ 以上의 初期時效段階에서 형성되는 G.P.B. (2) zones 등이었다. Slow reaction Stage 에서의 zone formation을 의한 活性化에너지는 0.26±0.04eV 였었으며 zone formation의 速度가 最大値를 갖는 臨界時效溫度는 70℃와 120℃ 사이에 存在하였다. 70℃와 같은 低溫에서의 長時間時效에서는 轉泣 loop와 loop free zone(L.F.Z.)이 형성되었고, 中間相 S 는 轉位線上에 析出하여 matrix의｛210｝面上에 <001> 成長方向으로 S` Composite precipitate sheets를 형성하였다. 平衡相 S 는 200℃ 以上에서의 長時間時效에서 析出하였다.

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.