Abstract
The repetitive corrugation and straightening process is a severe plastic deformation technique that is particularly suited to process metallic sheets. With this technique, it is possible to develop nano/ultrafine-grained structured materials, and therefore, to improve some mechanical properties such as the yield strength, ultimate tensile strength, and fatigue lifetime. In this study, an Al-6061 alloy was subjected to the repetitive corrugation and straightening process. A new corrugation die design was proposed in order to promote a heterogeneous deformation into the metallic sheet. The evolution of the mechanical properties and microstructure obtained by electron backscatter diffraction of the alloy showed a heterogeneous distribution in the grain size at the initial cycles of the repetitive corrugation and straightening process. Uniaxial tensile tests showed a significant increase in yield strength as the number of repetitive corrugation and straightening passes increased. The distribution of the plastic deformation was correlated with the hardness distribution on the surface. The hardness distribution map matched well with the heterogeneous distribution of the plastic deformation obtained by finite element simulation. A maximum average hardness (147 HV) and yield strength (385 MPa) was obtained for two repetitive corrugation and straightening cycles sample.
Highlights
The 6xxx series alloys are mainly used in the aircraft and automotive industry due to the good balance between mechanical strength, corrosion properties, and density
The finite element simulation showed a considerable degree of heterogeneity of the equivalent
The improvement of the mechanical properties was a consequence of the localization of the grain refinement in the highest deformed zones and intergranular misorientation
Summary
The 6xxx series alloys are mainly used in the aircraft and automotive industry due to the good balance between mechanical strength, corrosion properties, and density. The main mechanism for improving the strength of this alloy has been by precipitation hardening [1], but more recently, an alternative way of enhancing the mechanical properties is through the production of an ultrafine grain structure by severe plastic deformation (SPD). Different SPD processes attain a considerable grain refinement, such as equal channel angular pressing (ECAP), high-pressure torsion (HPT), accumulative roll bonding (ARB), repetitive corrugation and straightening (RCS), and constrained groove pressing (CGP) [2,3,4,5]. The ARB process consists of a repetitive procedure of cutting, stacking, and roll bonding between two sheets [5,6]. The CGP and RCS techniques consist in bending and straightening the workpiece without a significant change in the cross-section, the main difference between these techniques is that in the CGP, the dies are designed to constrain the elongation in the transversal or width directions during the pressing, while in the RCS any constraint is permitted
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