Revealing Hetero-Deformation Induced (HDI) Hardening and Dislocation Activity in a Dual-Heterostructure Magnesium Matrix Composite

Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites. However, the relationship between hetero-deformation induced (HDI) strain hardening and dislocation activity caused by heterogeneous structures in the magnesium matrix composite remains unclear. In this study, a dual-heterogeneous TiC/AZ61 composite exhibits significantly improved plastic elongation (PEL) by nearly one time compared to uniform FG composite, meanwhile maintaining a high strength (UTS: 417 MPa). This is because more severe deformation inhomogeneity in heterogeneous structure leads to more geometrically necessary dislocations (GNDs) accumulation and stronger HDI stress, resulting in higher HDI hardening compared to FG and CG composites. During the early stage of plastic deformation, the pile-up types of GND in the FG zone and CG zone are significantly different. GNDs tend to form substructures in the FG zone instead of the CG zone. They only accumulate at grain boundaries of the CG region, thereby leading to obviously increased back stress in the CG region. In the late deformation stage, the elevated HDI stress activates the new 〈c + a〉 dislocations in the CG region, resulting in dislocation entanglements and even the formation of substructures, further driving the high hardening in the heterogeneous composite. However, For CG composite, 〈c + a〉 dislocations are not activated even under large plastic strains, and only 〈a〉 dislocations pile up at grain boundaries and twin boundaries. Our work provides an in-depth understanding of dislocation variation and HDI hardening in heterogeneous magnesium-based composites.