Micro-Crystallographic Analysis of Shear Band Formation Mechanism in Cold Rolled Al-Sc Alloys at Different Precipitation States

The debate on whether the slip in Shear Bands (SBs) is crystallographic or non-crystallographic has continued for decades. In the present study, shear banding in cold-rolled Al-0.2 wt.% Sc alloys with different precipitation states were characterized to elucidate the mechanism of SBs formation and propagation across grain boundaries. The generated SBs are observed only in grains of S {123} and Copper {112} orientation. The orientation of SBs in the S orientation grains is close to R {142} , while the SBs in Copper orientation grains possess an orientation close to D {11 4 4} . This orientation dependency is proven to in tight association with asymmetric slips and local lattice reorientation. A periodic change in the slip systems is accompanied by a periodic change in the lattice orientation between parallel SBs. Through conducting the focussed ion beam (FIB) lift-out method and TEM analysis, the dislocations and slip activation in/around SBs are revealed. The results indicate that a sudden change in the slip path during deformation leads to flow localization, contributing to the formation of SBs. In this process, fine Al3Sc precipitates are characterized to promote the formation of SBs through inhibiting the dynamic recovery. The mechanism of SBs formation is crystallographic as the slip in SBs occurs on {111} planes with local lattice reorientation and the SBs propagation across grain boundaries is also driven by the slip on {111} planes. Furthermore, the effects of SBs on texture evolution are discussed as well.