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Investigation on Modeling and Analytical Study and Bonding of Multi-Layer Copper-Austenitic Stainless Steel Roll Bonded Sheets

Nouripour, Mohammad Hossein | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52434 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Akbarzadeh, Abbas
  7. Abstract:
  8. In the roll bonding process, the same and non-homogeneous metals are bonded to each other by rolling deformation, and the sheet produced exhibits multi-properties. Two- and three-layer copper and stainless steel sheets are used for a variety of purposes. Stainless steel-Copper bilayer sheets are not just cost effective in production, but also have mechanical and thermal benefits from the inherent properties of copper and stainless steel. In addition to its increased strength, good ductility, reduced thermal expansion and excellent soldering are other benefits. In the past, some researchers have been studied on the bonding strength and formability of austenitic stainless steel-copper bilayer sheets. However, all the process variables of this type of sheets have not been properly investigated, including the thickness of the layers. In this study, we tried to investigate the bond strength and formability of the sheet with an initial thickness ratio of 10 (copper to austenitic stainless steel). In spite of unsuccessful bonding of 316L austenitic stain steel and copper in lab conditions, aluminum foil with 50 μm thickness was used as an intermediate for successful bonding between 316L and copper. In order to investigate the effect of heat treatment on bonding strength, temperatures among 150-450 °C were investigated. Microscopic observations indicated that the copper-aluminum interface was separated at temperatures above 400 °C. By increasing the heat treatment temperature from room temperature to 250 °C, the surface diffusion reached to more than 3 μm and its bonding strength increased from 43 to 50 N/cm. By exceeding the heat treatment temperature from 250 °C the diffusion width increased and the bonding strength decreased. The results in the FLD showed low values of formability, representing the effect of prestraining in rolling direction on the changing the strain path of sheet deformation. The simulation of Nakazima test was carried out in ABAQUS software completely including drawbead area and two approach for sheet modeling, equivalent layer shell and two layer composite shell. For determining the FLCs, two new necking theory based on strain time history were used. For equivalent layer model, FLCs obtained based on necking theory which predict beginning of necking when abruptly changing in thinning rate observed, had good compatibility with experimental results in positive strain paths but the other necking theory, necking at extremum of the most acceleration of principal major strain, predicted higher value of formability. For two composite layer model, the second necking theory had better compatibility with experimental results than first necking theory in positive strain paths. Overall, the two-layer composite sheet model provided better matching results than the equivalent layer sheet. The results for both model and both necking theory had not suitable estimation in negative strain paths and predicted less formability than experimental results
  9. Keywords:
  10. Roll Bonding ; Simulation ; Austenitic Stainless Steel ; Necking Model ; Formability ; Laminated Sheets

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