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 (WQ) 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.

The microstructure and mechanical properties of 7075 and 7N01 alloys after multi-directional forging (MDFing) and subsequent aging were systematically investigated. The number density of the precipitates in the aged samples after MDFing were lower than that of the aged sample without MDFing. The aged 7075 and 7N01 alloys after MDFing showed the ultimate tensile strengths of 556 MPa and 428 MPa, respectively. The fatigue tests were conducted in air and 3.5% NaCl aqueous solution to investigate the effect of MDF on the fatigue properties of 7000 series alloys. As a result of fatigue test in air, the fatigue strength of the MDFed 7N01 alloy was slightly lower than that of non-MDFed one, but that of the 7075 alloy showed no difference before and after MDFing. Two alloys had no significant difference in fatigue crack growth rate in air and 3.5% NaCl aqueous solution.