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Evaluation of Bonding and Mechanical Properties of Metal-Polymer Sheets Manufactured by Roll Bonding

Rezaei Anvar, Behrouz | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 48524 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Akbarzadeh, Abbas; Kokabi, Amir Hossein
  7. Abstract:
  8. Emission of the greenhouse gases is a great concern and use of lightweight materials in transport vehicles has found a major importance in this respect. Metal/polymer laminated composites are of great interest due to their special mechanical properties and thoughness. Application of metal/polymer sheets is limited because of low bonding strength of metals and polymers in these sheets, which is not sufficient, to endure the stresses and strains during deformation processes such as deep drawing and bending. In this research, roll bonding of AA5052/Polypropylene sheets is investigated and the effects of bonding parameters on strength are evaluated and finally the bonding mechanisms during the roll bonding are expressed. The surface roughness or surface energy of the AA5052 sheets, rolling temperature (or, in fact, viscosity of the polymer layer) and the polymer chemical compositions (from surface energy and viscosity viewpoints) are considered as the main effective variables on the bonding. The structural and microstructural features of the bonding are investigated by optical, field-emission scanning electron (FE-SE) and transmission electron (TE) microscopes. T-peel and shear-tension tests are also used for evaluation of the bonding between the AA5052 and polypropylene as mechanical properties criteria. It is shown that, increase of the AA5052 surface roughness from 0.29 to 3.33 μm results in increase of the bonding strength by 300 percent. This is related to mechanical interlocking, increase of interfacial area and Van der Waals forces. However it can be said that effects of the surface area and Van der Waals forces are more than the mechanical inter locking, because even with minimum roughness a bond is created between the layers. The bonding strength is increased 300 percent by increase of the rolling temperature from 190 °C to 230 °C or by decrease of the polymer viscosity from 132.71 to 59.78 Pa.sec, with similar mechanical interlocking extent and complete contact between the layers. This is related to the presence of maleic anhydride chemical group in the polymer layer of these samples. When polymer viscosity is decreased, mobility of the maleic anhydride group is higher and then these chemical groups move and rotate easily toward the surface of AA5052 causing more interactions to it. Increase of the bonding strength with increasing the maleic anhydride groups in the polymer layer is in good agreement with this hypothesis. Higher content of the maleic anhydride results in increase of the bonding strength from zero to 3.03 MPa by enhancing the surface energy from 27.7 to 39 mN/m. This is accompanied with decrease of the complex viscosity from 384.03 to 59.78 Pa.sec which results in more interactions between the layers. This is proved by creation of an interfacial layer, increased diffusion distance of Al and a new chemical compound formed at the interface. It is shown by the experiments and simulations that mechanical properties of the 3 layered AA5052/PP sheets, such as bend ability and ultimate tensile strength (UTS) are related to the bonding strength between the layers. Increase of the bonding strength between the layers increases the mechanical properties because of higher strain compatibility between the layers and more plastic deformation of the samples by the tearing energy calculations. The damping capability is also increased 367 percent with higher bonding strengths. This is due to pronounced effect of the polymer layer by increasing the bonding strength and better transmission of the wave through AA5052 and PP interfaces. Accumulative roll bonding (ARB) of the AA5052 and polypropylene sheets (A-AP) was carried out on the samples with the best bonding conditions. For evaluation of these sheets, the results of microstructural investigation, tensile, micro hardness and damping tests are compared with the ARBed AA5052 sheets without polymer layer (A-AA). Grain size of the AA5052 sheets is finer in the A-AP composites because of more strain accumulated in the AA052 layers. Lower interfacial strength between the layers in the A-AP composites results in lower UTS in comparison to the A-AA composites. Higher strain and finer grain size of the AA5052 in the A-AP composites result in higher micro-hardness of the AA5052 in comparison to the A-AA composites. However, ultimate tensile strength of the A-AP composites is increased by 68 percent in comparison with the annealed AA5052 sheet. Damping capability of the A-AP is more than A-AA composites because of higher number interfaces and presence of the polymer layers. Furthermore, due to finer grain size of the AA5052 layers and multi interfaces between the layers during ARB damping capability is increased by 42 percent
  9. Keywords:
  10. Accumulative Roll Bonding (ARB) ; Mechanical Properties ; Roll Bonding ; Microstructure ; Aluminum/Polypropylene Multilayered Sheet ; Hybrid Materials

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