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.

Automated summary

This study systematically investigates the work hardening and strain delocalization in Al-5 wt.% CuO composite with intragranular nanoscale Al2O3 reinforcements. The results show that the geometrically necessary dislocation pile-ups at intragranular Al2O3 result in kinematic hardening, while the plastic relaxation dislocations generated by the release of internal stress contribute to isotropic hardening. The intragranular Al2O3 plays important roles in improving strain partitioning, stress transfer, and strength matching, contributing to the strength-ductility synergy in Al-5CuO.