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Parametric Investigation on Microstructure and Mechanical Properties of Ultrasonic Spot welded Aluminium and Copper Sheets

Yosefi, Ali | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54752 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossain; Abedini, Rezvan
  7. Abstract:
  8. Ultrasonic metal welding is a solid state welding process and is widely used in welding the connections of lithium-ion battery batteries in hybrid and plug-in hybrid vehicles. This welding process has advantages over fusion welding processes such as; Shorter time, no heat affected area, optimal energy consumption, cheaper equipment and no harm to the environment. The aim of this study was to investigate the effect and optimization of time, normal pressure and oscillation amplitude parameters in order to achieve the maximum tensile-shear test force and T-peel test in the dissimilar welding of 1050 aluminum and copper (purity above 99.9%). In order to achieve the optimal state of welding parameters and to study their interaction with each other, Design Expert 11 software and response surface method were used. The design of the experiment was performed using the response surface method with three variables in five levels, which include 20 welding modes. The selected range for welding parameters included time 0.2-1.2 seconds, pressure 2.8-6 bar and range amplitude 30-105%. To evaluate the mechanical properties of the weld, tensile-shear, T-peel test and microhardness tests were used. Stereo, optical and scanning electron microscopes were also used to observe the macrostructure and microstructure of the joint area, the cross section of the specimens and their fracture surfaces. The results showed that time and pressure are the most effective parameters with direct effect and also time, pressure and amplitude are the most effective parameters with direct effect on tensile-shear test force and T-peel test. The cross section of welded specimens includes bonded and unbonded areas, which with increasing the amount of effective parameters with direct impact, due to increased plastic deformation, bond density at the joint increased and the effective post-weld thickness after welding decreased. Low bond density specimens are known as under-weld and low effective thickness specimens are known as over-weld. Optimal mode in 1 second, 4.5 bar and 55% with maximum force obtained from tensile-shear test and T-peel test obtained at 810 and 150 N, respectively, with an error of less than 5% compared to the optimal mode predicted by the software. In general, with the increase of effective parameters, due to the increase in temperature and plastic deformation, the bonded areas have increased, increasing the bond density and maximizing the force obtained from mechanical tests. Then, increasing the value of the parameters causes softening and decreases the effective thickness of the sheet, and the amount of force obtained from the tensile-shear test and the pilot test decreases
  9. Keywords:
  10. Oscillation Amplitude ; Aluminum Alloy 1050 ; Pure Copper ; Joint Mechanical Properties ; Vertical Pressure ; Ultrasonic Metal Welding ; Aluminum-Copper Joint

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