Towards the work hardening and strain delocalization achieved via in-situ intragranular reinforcement in Al-CuO composite

Dense intragranular distribution of nanoscale reinforcements is highly desirable since it is effective in reconciling the strength-ductility trade-off in Al matrix composites (AMCs). Herein, we report a systematic investigation on the work hardening and strain delocalization in Al-5 wt.% CuO (Al-5CuO) composite with strength-ductility synergy contributed by in-situ dense intragranular nanoscale Al2O3. Results reveal that Al-5CuO exhibits prominent hetero-deformation induced (HDI) strengthening as indicated by its larger HDI stress than effective stress. We showcase that the notable pile-ups of geometrically necessary dislocations (GNDs) at intragranular Al2O3 result in the prevailing kinematic hardening. While the plastic relaxation dislocations (PRDs) around Al2O3 generated by the release of GND-induced internal stress produce isotropic hardening. Both contribute to the pronounced work hardening of Al-5CuO. Comprehensive characterizations suggest the GND distribution with marked intragranular feature in Al-5CuO during straining, which implies the effective provoking of grain interior rather than grain boundary (GB)/interfacial zone to take plastic strain. On basis of the well-described storage and annihilation of GNDs and PRDs at the intragranular Al2O3, the microstructure-based strain-hardening model enables an in-depth understanding of the kinematic and isotropic hardening contributions by Al2O3 in Al-5CuO. Systematic analysis further confirms the important roles of intragranular Al2O3 in improving the strain partitioning, strain/stress transfer and strength matching across different domains of Al-5CuO, which significantly contributes to strain delocalization and hence strength-ductility synergy. This work sheds important insights on the innovative design of strong and ductile AMCs with intragranular nanoscale reinforcements for structural applications.