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.

The limited creep resistance of wrought Mg–Al alloys restricts their lightweight applications at intermediate temperatures due to the softening effect of discontinuous precipitation (DP) on the dislocation-controlled creep. Here, we developed a creep-resistant wrought Mg–Al alloy through microalloying of Y and Ca. The resulting alloy exhibited an order of magnitude enhancement in the creep resistance at 125 ℃/50–100 MPa. In contrast to the grain boundary instabilities by DP in the previously reported wrought Mg–Al alloys, we show that the addition of 0.21Y+0.15Ca wt% produces a (Zn+Ca) co-segregation at the grain boundaries as a result of their segregation energy and the activation energy of grain boundary migration, thereby stabilizing the grain boundaries. The (Zn+Ca) co-segregation inhibits the dynamic DP and promotes the formation of intragranular Al-enriched clusters, which favorthe formation of Al₂Y, Mg₁₇Al₁₂ nano precipitates, thereby impeding intragranular dislocation motion during creep. Furthermore, the addition of 0.21Y+0.15Ca wt% facilitates the formation of a fine and uniform recrystallization structure in the microalloyed alloys compared to AZ80 due to the high activation energy of mobility for the (Zn+Ca) segregated grain boundary. Therefore, the microalloyed alloys exhibit good tensile properties with 380 MPa tensile strength and 18% elongation. Our constitutive analysis revealed that the (Y+Ca) microalloying decreased the creep stress exponent by 29% and increased the creep resistance in the medium to high-stress range. Microalloying provides a promising way to develop low-cost creep-resistant wrought Mg–Al alloys.