Trace Zr Addition Enhances Strength and Plasticity in Cu-Zr/Al2Cu/Al Alloys via Local FCC-to-BCC Transition: Molecular Dynamics Insights on Interface-Specific Deformation and Strain Rate Effects

This study investigates how Zr doping influences the deformation behavior of Cu-Zr/Al₂Cu/Al composites through molecular dynamics simulations. The impact of Zr content (ranging from 0 to 0.8 wt%) and strain rate on phase evolution, dislocation dynamics, and fracture mechanisms under vertical and horizontal tensile loading was examined. The results indicate that Zr doping achieves a balance between strength and plasticity by means of solute drag, amorphization, and phase competition. At a Zr concentration of 0.2 wt%, the formation of the body-centered cubic (BCC) phase reached a peak (22.04% at ε = 0.11), resulting in a maximum tensile strength of 9.369 GPa while maintaining plasticity due to limited face-centered cubic (FCC) decomposition. A moderate Zr content of 0.6 wt% maximizes strength through amorphization but significantly diminishes plasticity due to excessive FCC-to-BCC transitions. Higher Zr concentrations (0.8 wt%) lead to solute supersaturation, which suppresses phase transitions and slightly reduces toughness by causing hexagonal close-packed (HCP) phase accumulation. The strain rate markedly enhances both strength and plasticity in vertical loading by accelerating dislocation interactions. Vertical tensile deformation initiates brittle fracture, whereas horizontal loading results in ductile failure through sequential load transfer from Al₂Cu layers to Al/Cu interfaces, ultimately causing interfacial decohesion. These findings underscore the essential roles of Zr content and strain rate in modulating phase transformations and interface responses. The research offers a framework for creating gradient Zr-doped or multi-scale composites with optimized strength, plasticity, and damage tolerance suitable for aerospace and electronics applications, where trace Zr additions can reinforce Cu matrices.