Simultaneously enhancing the strength and ductility of as-extruded AlN/AZ91 composites via nano-precipitation and pyramidal slip

Age hardening is often used to optimize the mechanical properties of as-deformed Mg-based materials in industry, whereas the improvement of strength is usually accompanied by the significant loss of ductility, which hinders the application of Mg-based materials in structural components. In the present work, high strength-ductility synergy (the yield strength of 263 & PLUSMN; 9 MPa, ultimate tensile strength of 398 & PLUSMN; 7 MPa and elongation to fracture of 34% & PLUSMN; 1%) was realized in as-extruded AlN/AZ91 composites after optimizing aging processes. Microstructural characterization shows that AlN particles induced a large number of geometrically necessary dislocations around the AlN/Mg interface during extrusion, which decreased the nucleation barrier and provided more heterogeneous nucleation sites for & gamma;-Mg17Al12 continuous precipitation. Meanwhile, 95% of residual dislocations in as-extruded AlN/AZ91 composites were annihilated during peak-aging, suppressing the growth and coarsening of continuous precipitates. Therefore, high density of nano-sized & gamma;-Mg17Al12 continuous precipitates was produced in as-extruded AlN/AZ91 composites after peak-aging. During tension, gliding dislocations bypassed spherical & gamma;-Mg17Al12 nano-precipitates by Orowan looping rather than cutting mechanism, which induced a strong block on dislocation motion. So high yield strength was mainly attributed to the high density of non-shearable & gamma;-Mg17Al12 nano precipitates with spherical morphology, which was different from other Mg-Al-based systems. The results of texture evolution and slip trace analysis demonstrated that the suppression of extension twinning and less basal slip was due to the enhanced activity of pyramidal ( c + a ) slip in as-extruded AlN/AZ91 composites after peak-aging during the room temperature tension, meanwhile, the dislocation density of as extruded AlN/AZ91 composites was significantly decreased during peak-aging, then higher elongation to fracture was achieved.& COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.