Precipitation hardening of 2024-T3 aluminum alloy during creep aging

Exposure of Al–Cu–Mg alloys to an elastic loading, either for “creep age forming” or other manufacturing processes at relatively high temperature, will lead to microstructural changes in materials. Effects of the external stress and creep aging temperature on the hardness and precipitation process in a typical Al–Cu–Mg alloy (2024-T3 aluminum alloy) were studied by uniaxial tensile creep experiments. Also, the effects of aging temperature on the age-hardening curves of 2024-T3 aluminum alloy were studied by stress-free-aged experiments. It is found that the precipitation process is very sensitive to the external stress and aging temperature. Temperatures of 423, 448, and 473 K are validated as the “under aging”, “peak aging” and “over aging” temperatures, respectively. An external stress can accelerate the precipitation hardening (also called age hardening) of 2024-T3 aluminum alloy. The large external stress and high aging temperature easily make the preferential precipitation process as SSS→GPB→S″→S′→S, and S phase (Al2CuMg) is the main precipitate under the experimental conditions. With the increase of the external stress and creep aging temperature, S phase easily grows up and coarsens. Meanwhile, the creep aging treatment results in the discontinuous distribution of precipitation phases on grain boundaries, which can improve the corrosion-resistance of 2024-T3 aluminum alloy.