Effect of various aging treatment on thermal stability of a novel Al-Zn-Mg-Cu alloy for oil drilling

Abstract 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.