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Investigation on Interfacial Reactions in Aluminium to Copper Resistance Spot Welding

Zare, Mohammad | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52871 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid
  7. Abstract:
  8. With the development of electrical engineering and the electrical industry, the use of copper and its alloys has grown tremendously. On the other hand, with development and modern industry, it will be difficult to meet the requirements such as high performance, cost reduction and weight reduction of the structure if only one metal material is used in the production of the desired component or structure. Aluminum can be used in combination with copper because of its properties such as high thermal and electrical conductivity. Al/Cu bonding is used in industries such as microelectronics, automobiles and batteries. This study has investigated parametrically the feasibility of uneven bonding of these metals using resistance spot welding process. The present study was conducted in three phases. In the first phase, aluminum and copper metals are directly bonded, and it has been shown that the mechanical properties of the joint, such as shear and cross tension and hardness, are affected by physical and metallurgical parameters: (1) with increasing The heat input, nugget diameter, and electrode penetration into the base metal are increased, resulting in the failure mode switching from IF to PIF mode. (2) As the heat input increases, the microstructure of the nugget undergoes changes. At low heat inputs, most of the nugget volume forms the single-phase region of α-Al. As the heat input increases, the growth of the intermetallic compounds increases and the nugget region becomes larger. In the second phase, the cover sheet technique was used. By applying this technique, an additional heat source is introduced into the system. Thus, the contribution of copper during the bonding process is reduced, and the current required for binding is reduced from 18 kA to 11 kA. Because of this phenomenon, intermetallic compounds have grown and also increased the diameter of the nugget, and ultimately, has reduced the tensile strength. This decrease in shear tensile strength can be attributed to increased electrode penetration and high growth of intermetallic compounds, but at the same time, increased hardness values and improved tensile properties. In the third phase, the interlayer of zinc is applied. Zinc has acted as a chemical barrier in this case. The use of a zinc interlayer and a cover sheet technique reduced the current required for welding and achieved the first connection at a current of 7 kA. In this case, the zinc element reacts with the copper oxide layer, improving the wettability and increasing the nugget diameter. The tensile-shear properties decreased in this case, while the tensile properties improved and all fractures occurred as IF
  9. Keywords:
  10. Resistance Spot Welding ; Interlayer ; Copper ; Intermetallic Compounds ; Aluminum Alloy ; Aluminum-Copper Dissimilar Welding ; Cover Sheet Technique

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