7xxx series aluminum alloys are critical structural materials in aerospace applications, but their susceptibility to hydrogen embrittlement (HE) poses significant challenges to service safety and durability. The effects of Si, Er, and Zr microalloying, combined with optimized heat treatments on the HE resistance of Al–Zn–Mg–Cu alloys, were systematically investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and mechanical testing. Three alloys—1# (AlZnMgCuZr), 2# (AlZnMgCuErZr), and 3# (AlZnMgCuSiErZr)—were subjected to single-stage or two-stage homogenization, followed by solution treatments at 470 °C/2 h and 540 °C/1 h, and peak aging at 125 °C. The hydrogen charging experiment was conducted by first applying a modified acrylic resin coating to protect the gripping sections of the specimen, followed by a tensile test. Results demonstrate that alloy 3# with Si addition exhibited the lowest RA_loss, followed by the 2# alloy, which effectively improved the alloys’ hydrogen embrittlement behavior. Compared with the solution in 470 °C/2 h, the 540 °C/1 h solution treatment enabled complete dissolution of Mg₂Si phases, promoting homogeneous precipitation and peak hardness comparable to alloy 2#. Two-stage homogenization significantly enhanced the number density and refinement of L₁₂-structured Al₃(Er,Zr) nanoprecipitates. Silicon further accelerated the precipitation kinetics, leading to more Al₃(Er,Zr) nanoprecipitates, finely dispersed T′/η′ phases, and lath-shaped GPB-II zones. The GPB-II zones effectively trapped hydrogen, thereby improving HE resistance. This work provides a viable strategy for enhancing the reliability of high-strength aluminum alloys in hydrogen-containing environments.

Achieving a balanced combination of mechanical performance and corrosion resistance remains a critical challenge restricting the broader application of Al–Zn–Mg–Cu alloys in aerospace, marine, and transportation industries. In this investigation, the addition of Si significantly enhances the mechanical properties of the alloy. Among them, the alloy containing 0.35Si has the best corrosion resistance, which is closely related to the transformation of precipitates. A non-monotonic relationship between Si content and corrosion resistance was observed. At low Si levels, the simultaneous precipitation of η, T, and GPB-II phases leads to a large electrochemical potential difference among these phases, which promotes micro-galvanic corrosion. With increasing Si content, the microstructure evolves toward the dominance of GPB-II precipitates, thereby reducing the internal potential difference and improving corrosion resistance. However, excessive addition of Si will lower the equilibrium solid phase temperature, resulting in overburning during the solid solution treatment process and a significant decrease in corrosion resistance. In addition, lowering the solution treatment temperature effectively improves corrosion resistance by suppressing the formation of remelted spheres and low-melting-point brittle phases along grain boundaries. These phases can form strong micro-galvanic couples with the matrix, accelerating anodic dissolution. Therefore, by adding an appropriate amount of Si and optimizing the solid solution temperature, a corrosion-resistant high-strength Al-Zn-Mg-Cu-Si alloy can be obtained. This strategy also provides a broader compositional and heat-treatment design window, which could be further expanded through the incorporation of rare-earth (RE) elements.