Superior strength-ductility synergy of layered aluminum under uniaxial tensile loading: The roles of local stress state and local strain state. (May 2022) - Xia, Yiping
Highlights: Layered Al shows a good strength-ductility synergy compared to homogeneous Al under uniaxial tension. The comparison between classical SFs and mGSFs for prediction of activated slip systems unravels the presence of multiaxial local stress state. A transformation of local strain state from uniaxial to biaxial stretch is revealed by DIC method. The formation of multiple deformation microbands is revealed by the quasi in-situ EBSD coupled with a novel misorientation mapping method. Taylor ambiguity method with such local strain state agreed well with the multiple microbands formation. Abstract: A typical layered Al composed of alternating fine-grained layers (FLs) and coarse-grained layers (CLs), fabricated by hot pressing and hot rolling, exhibits a superior strength-ductility synergy under uniaxial tensile loading compared with monolithic Al. The mechanism behind the excellent mechanical properties was elucidated from the perspective of local stress state and local strain state. We found that the operative slip systems of CLs cannot be predicted by the classical Schmid factor, indicating a complex local stress state differing from global uniaxial tension. The so-called local multiaxial stress state, probably caused by the deformation incompatibility between constituent layers, was then proposed, and proved feasible for predicting the slip systems in CLs. On the other hand, the digital image correlation revealed that the strong strain partitioning leads to the transformation of local strain state on CLs from uniaxial to biaxial stretch despite under uniaxial tensile loading. Such the local strain state was incorporated into the Taylor ambiguity method, which can derive magnitudes of operative slip systems in the CLs grains with different orientations. The Taylor ambiguity results agreed well with the multiple microbands formation revealed by the quasi in-situ electron backscatter diffraction coupled with a novel misorientation mapping approach. The characteristic slip system activation and dislocation microbands governed by the local stress state and local strain state imply more latent hardening, hence enhancing the strain hardening capability of layered Al. Our work provides a new direction to achieve a superior strength-ductility synergy by designing local stress/strain and tailoring corresponding deformation mechanisms. Graphical abstract: Image, graphical abstract