Enhanced strength and ductility AZ91 alloy with heterogeneous lamella structure prepared by pre-aging and low-temperature extrusion

In this study, AZ91 alloy with heterogeneous structure comprised coarse, fine grained layers and the heterogeneous precipitates was obtained via pre-aging and low-temperature extrusion. The aging prior to extrusion (APE) sample with heterogeneous lamella structure presented an optimum combination of ultimate tensile strength (405.3 MPa), yield strength (216.5 MPa) and elongation (18.5%), which are much superior than extrusion (E) and extrusion prior to aging (EPA) samples with homogeneous structure. The observed excellent mechanical properties stemmed from the synergy effect of more stable precipitations at low temperature extrusion, grain refinement and texture. Meanwhile, heterogeneous deformation-induced (HDI) strengthening and work hardening also play a significant role on improving mechanical properties. The macroscopic and microscopic strain distributions demonstrate that APE sample is conducive to strain transfer and alleviate local stress concentration during collaborative deformation of coarse and fine grained layers, resulting in the improvement of strength and ductility. The research of this work will enrich the preparation methods of heterogeneous materials with intense precipitation strengthening potential.