Impact of Y and Er on recrystallization behavior and mechanical properties of AA7085/Al₂O₃ + ZrB₂ composites

This study reveals the essential role of rare-earth elements (RE) in regulating the microstructure and mechanical properties of aluminum metal matrix composites (AMMCs), through precise control of segregation and recrystallization processes. This study investigates the effects of trace additions of Yttrium (Y) and Erbium (Er) on the microstructural evolution, dynamic recrystallization (DRX), and mechanical properties of AA7085 Al alloy reinforced with 3 vol% Al₂O₃ and ZrB₂ nanoparticles (AZ composite). The composites were fabricated using in-situ synthesis and subjected to hot rolling with an 80 % reduction followed by T6 heat treatment. Microstructural analyses revealed distinct segregation behaviors of Y at grain boundaries, driven by their difference in free energies of segregation and elastic strain energies. Whereas, Y promoted the formation of Al₈Cu₄Y phases, leading to enhanced grain boundary strengthening, however, the strong solute drag effect suppressed DRX and consequently resulted in increased residual stress levels. Conversely, Er facilitated efficient DRX, resulting in finer, equiaxed grains and improved grain refinement through dynamic recovery mechanisms. The AZ-Y composite exhibited superior UTS, while the AZ-Er composite demonstrated enhanced ductility, both composites showing significant mechanical property improvements compared to the baseline AZ composite. These improvements are attributed to the refined microstructure, higher dislocation density, and enhanced precipitation strengthening, emphasizing the importance of RE elements in AMMCs.