Deformation faulting in ultrafine-grained aluminum alloys: Nucleation mechanisms and critical assessment of strengthening-ductilization contributions

Stacking faults (SFs) have received a growing attention in recent years, and are currently incorporated in microstructure design to achieve a synergistic enhancement of strength and ductility for critical applications. However, unlike extensively studied nanotwins, the full potential of SFs in face-centered-cubic (fcc) metallic alloys, particularly in high stacking fault energy fcc Al-based materials, has remained less-explored and unutilized. In the present work, we engineered SFs-containing high-strength ultrafine-grained Al-Mg based alloys by extrusion deformation of mechanically alloyed powder compacts. These SFs tend to emit from grain boundaries (GBs) and matrix/precipitate interfaces during the extrusion deformation, exhibiting a heterogeneous spatial distribution in the resultant microstructures. Through theoretical analysis of the strengthening effects associated with diverse structural elements and detailed microscopic observations of SFs in the macroscopically yielded specimens, we find that GB- and hetero-interface-emitted SFs are incapable of providing substantial strengthening, but can effectively improve the plasticity of the materials. This finding is fundamentally inconsistent with the reported Al-based materials with SFs in which SFs are proposed to simultaneously enhance materials’ strength and plasticity. Hence, our results advance the current understanding of the role of SFs in modulating ductility of high-strength Al-based alloys by interface-emitted SFs.