Abstract: In this work, we introduced pure Ti into AZ31 Mg alloy by extrusion process followed by annealing at 350 °C for 1 h to significantly improve the mechanical properties of AZ31 laminate, with a yield strength of 243 MPa, an ultimate tensile strength of 338 MPa and a uniform elongation of 17.7%. Microstructural characterizations showed that there was slight diffusion of elements (Al, Zn, and Mn) across the layer interface, and the interface between the constituent layers maintained semi-coherent. Moreover, significant microstructure heterogeneities appeared across the hetero-interface, where the Mg layer possessed large equiaxed grains with lower dislocation density, while the Ti layer formed ultrafine grains (UFG) and unrecrystallized block grains with extensive dislocation cells and dislocation walls. Combining the digital image correlation (DIC) technique and in-situ electron backscatter diffraction (EBSD), it was found that the microstructural heterogeneities induced significant strain gradients near the layer interface during plastic deformation, which needed to be accommodated by geometrically necessary dislocations (GNDs). This resulted in hetero-deformation-induced (HDI) strengthening and HDI strain hardening to strengthen and toughen the AZ31 laminated composite. Additionally, the introduction of the Ti layer effectively hindered the propagation of the cracks and consequently improved the ductility of the laminate.

Key words: AZ31 laminated composite, Extrusion, Annealing, Strain gradient, Mechanical properties