Abstract
This paper addresses localized plastic flow during equal-channel angular pressing (ECAP) of an AA6060 aluminum alloy. We observe an alternating formation of shear bands and matrix bands during ECAP that leads to pronounced strain partitioning without cracking. Local deformation is analyzed by considering the distortion of indents along flow lines in the center of a split billet. We estimate equivalent strains of about 3.6 inside the shear bands, whereas plastic deformation in the adjacent matrix bands is almost negligible. Microstructural analysis by SEM and STEM confirms that the shear bands exhibit typical features of severely plastically deformed microstructures at the onset of forming an ultrafine-grained microstructure. We further present statistics of band widths, and we discuss the roles material hardening as well as ECAP die geometry (in terms of the inner die radius) in facilitating the recurrent localized deformation that, in the absence of crack nucleation, leads to the production of an interesting and novel type of bulk-laminated materials by ECAP.
Highlights
Localization of deformation is a common phenomenon in materials science; examples include Lüders bands [1], Portévin-Le Châtelier bands [2,3], or martensite bands related to the stress-induced phase transformation
The experimental and numerical results presented in this paper address a novel phenomenon during equal-channel angular pressing (ECAP) of a cold-worked AA6060 alloy: strain partitioning by recurrent formation of shear bands and matrix bands
Plastic deformation in the shear bands is significantly larger than expected for a single ECAP pass in a 90° die, and this excessive straining is counter-balanced by considerably smaller amounts of straining in the matrix bands
Summary
Localization of deformation is a common phenomenon in materials science; examples include Lüders bands (in mild steels) [1], Portévin-Le Châtelier bands (e.g. in aluminum alloys) [2,3], or martensite bands related to the stress-induced phase transformation (e.g. in shape memory alloys [4,5,6]). In many cases, localized deformation is directly related to material failure. This is, for instance obvious, for adiabatic shear bands formed at high strain rates, where a locally increased amount of plastic deformation results in (locally) more pronounced energy dissipation, a (local) increase of temperature, and in (locally confined) thermal softening that in turn leads to an even more pronounced concentration of further deformation inside the forming shear band [7,8]. We analyze local deformation by considering the distortion of indents in a split billet, and we discuss the resulting microstructural features of shear vs matrix bands. We briefly discuss two potential factors that influence the recurrent formation of shear and matrix bands, material hardening capacity and ECAP die geometry
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