The effect of the copper and magnesium contents and quenching rate during quenching on the artificial age hardening behavior of Al-Cu-Mg alloys was investigated. For the higher copper-containing specimens as conventional 2000 series aluminum alloys, like AA2024, precipitation of the stable phases increased as the quenching rate decreased under the as-quenched conditions. The maximum hardness after the artificial aging of air cooled (AC) specimens was much lower than that of the water quenched

more »

... Q) specimens. On the other hand, for the lower copper-containing specimens, coarse precipitation did not increase even in the case of the AC specimens. The age hardening behaviors of the WQ and AC specimens were very similar such that the maximum hardness and aging rate were almost the same. Many parts of the fine precipitates that increased the hardness were thought to be the GPB zone or fine S phase for the WQ specimens and relatively coarse S phase for the AC specimens. From the calculated CCT diagrams, the lower copper-containing specimens could maintain the copper and magnesium in the solid solution state during air cooling, so they could be quenched at a rather slower quenching rate like air cooling.