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Effect of severe plastic deformation on evolution of intermetallic layer and mechanical properties of cold roll bonded Al-Steel bilayer sheets

Dehghanpour Baruj, H ; Sharif University of Technology | 2020

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  1. Type of Document: Article
  2. DOI: 10.1016/j.jmrt.2020.08.033
  3. Publisher: Elsevier Editora Ltda , 2020
  4. Abstract:
  5. In this study, evolution of intermetallic layer of the cold roll bonded bilayer of Aluminum-Steel sheets, during severe plastic deformation (SPD) followed by annealing has been investigated. The effect of such evolution on mechanical properties has been discussed. For this purpose, Constrained Groove Pressing (CGP) was used as a SPD process. Field emission scanning electron microscope equipped with energy dispersive spectroscopy and optical microscopy were used for examination of intermetallic compounds morphology and composition. Meanwhile, tensile properties of the bilayer sheets were evaluated. According to microstructural observations, continuous intermetallic layer was formed during rolling and annealing processes. This intermetallic layer was completely cracked into very fine particles after the first pass of CGP. Some of these intermetallic compounds were pushed into the base layers by the shear stress and some of them remained at the interface. Moreover, it was observed that during the CGP process, at the interface and between remaining intermetallic compounds and fresh surfaces of both Al and steel, new bonds were formed. After formation of such new bonds and during the second step of the CGP process, flattening process, mechanical interlocks were created. However, after the second CGP pass, no intermetallic compound was observed at the interface yet delamination was seen. Due to formation of intermetallic compounds at the bonding area and the vicinity of it, reinforced area, mechanical interlocks and higher dislocation density in that region, the ultimate tensile strength (UTS) increased after the first pass of CGP, but due to delamination, it decreased in second pass. The effect of evolution of bond structure on the tensile strength was measured by using bonding portion (BP) criterion defined as the difference in the UTS of the bonded versus non-bonded samples undergone similar deformation and annealing treatment. The BP values show similar trend to the UTS data, increased at the first pass and decreased at the second pass. In the following study, the CGPed samples have been annealed in order to recover the intermetallic layer. The CGPed samples were annealed at 350 ◦C, 400 ◦C and 450 ◦C for 30, 60 and 90 min. The optimum thickness of 2.6 μm was observed at the 450 ◦C in 30 min annealing treatment. The UTS, BP and elongation to break increased 7%, 32% and 60%, respectively, in comparison to those of the as-CGPed sample. © 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
  6. Keywords:
  7. Aluminum ; Bilayer sheet ; Roll bonding ; Severe plastic deformation (SPD) ; Steel ; Aluminum coated steel ; Aluminum sheet ; Annealing ; Cold rolled steel ; Energy dispersive spectroscopy ; Optical emission spectroscopy ; Plastic deformation ; Scanning electron microscopy ; Shear stress ; Tensile strength ; Constrained groove pressing ; Dislocation densities ; Field emission scanning electron microscopes ; Mechanical interlock ; Micro-structural observations ; Morphology and composition ; Severe plastic deformations ; Ultimate tensile strength ; Intermetallics
  8. Source: Journal of Materials Research and Technology ; Volume 9, Issue 5 , 2020 , Pages 11497-11508
  9. URL: https://www.sciencedirect.com/science/article/pii/S2238785420316409