Deformation mechanism of multi-DoF formed AZ91 alloy with heterogeneous microstructure

• AZ91 alloy with heterogeneous microstructure is deformed to different strains during room-temperature tensile test. • The heterogeneous microstructure is ever-present despite of the increasingly coarsened small and large grains. • The basal texture which is detrimental to ductility is always not generated. • Strength-ductility synergy is due to heterogeneous microstructure, precipitated phase and non-basal slips activation. Strength-ductility trade-off is a prominent problem that severely limits application of magnesium alloys, which has been effectively solved by introduction of heterogeneous microstructure. However, deformation mechanisms responsible for strength-ductility synergy remain unclear. Herein, multi-degrees of freedom (multi-DoF) formed AZ91 alloy with heterogeneous microstructure, exhibiting extraordinary strength-ductility synergy, was deformed to intermediate strains of 3%, 6%, 9%, 12% and 15% and failure strain at 18%. With tensile strains increasing, both small and large grains in heterogeneous microstructure exhibit progressive coarsening, with the proportion of small grains decreasing and that of large grains increasing. Nevertheless, the microstructure retains heterogeneous during the whole tensile deformation. Initially multi-DoF formed AZ91 alloy is characterized by a dominant prismatic texture, some pyramid texture and little basal texture. The familiar basal texture which is generally formed during room-temperature deformation is not generated. Instead, texture transformation occurs only between prismatic and prismatic textures, primarily due to the activation of non-basal slips. Overall, prismatic texture remains predominant, with its area fraction ranging from 81.5% to 90.1% across all strain levels. The ever-present heterogeneous microstructure and activation of non-basal slips co-contribute strength-ductility coordination improvement in the multi-DoF formed AZ91 alloy.