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Abstract: The effect of artificial aging treatment on fatigue crack propagation (FCP) resistance of an Al–Cu–Mg alloy was investigated. It was shown that FCP rate of artificially aged alloy in the Paris region is lower than that of naturally aged alloy before and after thermal exposure. During the thermal exposure, tensile strength of artificially aged alloy remained unchanged. The results of three-dimensional atom probe (3DAP), transmission electron microscope (TEM) and differential scanning calorimeter (DSC) analysis showed that Cu–Mg co-cluster in artificially aged alloy are larger than that in natural aged alloy and can stably exist during thermal exposure. Size of Cu–Mg co-cluster was found to be the main factor influencing the thermal stability of Cu–Mg co-cluster and the FCP resistance. [Copyright &y& Elsevier]

Thermal stability plays an important role in practical application of Al-Zn-Mg-Cu alloy for oil drilling. In this work, a new four-stage aging treatment by employing a natural aging prior to re-aging is designed to improve thermal stability of Al-Zn-Mg-Cu alloy. The effect of T6, four-stage aging, three-stage aging and T74 on thermal stability was investigated by tensile testing, transmission electron microscopy (TEM) and atom probe tomography (APT). The results showed that after thermal exposure at 120 °C for 500 h, the tensile strength of the four-stage aged sample decreased only by 5.05%. APT analysis indicated that natural aging accelerates the diffusion of Mg atoms, and promotes the precipitation of GP zones during re-aging stage, and TEM observations also supports this result. Natural aging for 24 h prior to re-aging enhance the formation of GP zones, leading to an effective improvement of the strength properties and thermal stability of the studied alloy. In addition, precipitates in all aging samples gradually coarsen with the thermal exposure time increase. The influence of precipitates on mechanical properties of the investigative alloy after thermal exposure is also discussed. [ABSTRACT FROM AUTHOR]

Microstructures and mechanical properties of Al-Cu-Mg alloys containing various Ag additions were investigated by a combination of the tensile testing and quantitative transmission electron microscopy (TEM) analysis. Our results indicated that an increase of Ag from 0.46 to 0.88wt% promoted the precipitation of Ω phase, thereby leading to the noticeable improvement on the strength properties of the underaged Al-Cu-Mg alloys at various temperatures. This enhanced precipitation of Ω phase was also accompanied by the suppressed formation of θ' phase. Despite further exposing at 300°C lead to a pronounced decrease in the number density of Ω phase, the higher plate number density was still revealed in 0.88Ag alloy rather than 0.46Ag alloy. Moreover, quantitative TEM results of the studied alloys highlighted the differences in the coarsening kinetics of Ω phase during further exposing at 300°C. Ω phase tended to experience a transition from the plate thickening to the plate lengthening by increasing Ag at 300°C. Our results also present the positive effect of pre-aging at 165°C for 2h on retarding the thickening kinetics of Ω phase at 300°C. [ABSTRACT FROM AUTHOR]