Simultaneous enhancement of mechanical and fatigue properties in 2xxx aluminum alloys via microstructural uniformity induced by cyclic plasticity

The 2xxx (Al-Cu-Mg) alloy is widely used in transportation fields due to its excellent strength-to-weight ratio. However, conventional heat treatments such as peak aging (PA) often result in a pronounced strength-ductility trade-off and limited fatigue resistance. To address these limitations, this work presents a comprehensive study on the mechanical properties and fatigue behavior of Al-Cu-Mg alloy subjected to a cyclic plasticity treatment. The cyclic strengthened (CS) samples exhibit a well-balanced combination of strength and ductility due to the formation of nanoscale solute clusters. A systematic and quantitative analysis of the strengthening mechanisms is performed to evaluate the contributions of key microstructural features to the mechanical response. Moreover, the CS samples also demonstrate a significantly higher fatigue ratio and fatigue strength compared to the PA sample, despite exhibiting comparable tensile strength. These improvements are attributed to the absence of weak precipitate-free zones (PFZs) induced as a result of cyclic plasticity, which completely eliminates the pronounced strength differential between the grain interiors and the PFZs observed in the PA state. This microstructural uniformity effectively suppresses strain localization under cyclic loading, promotes a more homogeneous strain partitioning, and consequently delays fatigue crack initiation. These findings highlight cyclic plasticity treatment as a promising microstructure design strategy for simultaneously enhancing the mechanical and fatigue properties of high-strength Al alloys.