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Microstructural Investigation of the Cu–Al Joint Interface in Fusion Welding

Pagard, Vahid | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58359 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid
  7. Abstract:
  8. The joining of dissimilar metals such as copper and aluminum has always been one of the major challenges in various industries, including automotive, electronics, and aerospace. This challenge primarily arises from the fundamental differences in the physical and chemical properties of these two metals. Cu is well known for its exceptionally high electrical and thermal conductivity, whereas Al, with its lower density, superior corrosion resistance, and favorable mechanical properties, is widely used in many applications. However, the significant differences in thermal expansion coefficients, thermal conductivity, and the tendency to form brittle intermetallic compounds during the joining process make it difficult to achieve a strong and durable bond between these two metals. In this study, to overcome the challenges of joining Al and Cu in fusion welding processes, electroless nickel coating was applied to the copper surface, and an ERNi-1 filler metal was employed. The purpose of using these layers was to control the growth of intermetallic compounds, improve the wettability of the interface, and consequently enhance the joint strength. The welding process selected was Gas Tungsten Arc Welding (GTAW), which is one of the common and effective methods for producing high-quality joints in dissimilar metals. To more accurately evaluate the effectiveness of these methods, two types of joints, liquid Al solid Cu and liquid Al liquid Cu, were examined and analyzed. The results indicated that the presence of the electroless nickel layer significantly reduced the thickness of the brittle intermetallic compound layers and facilitated the formation of new phases such as (Cu)AlNi, (Cu,Ni)Al, and Al₇Cu₄Ni. Due to their more stable and ductile metallurgical structures, these compounds exhibited superior mechanical properties compared to the brittle Al₂Cu phase commonly observed in direct joints. Tensile test results revealed that the use of ERNi-1 filler metal in liquid Al to liquid Cu joints led to the highest tensile strength of 75 MPa (equivalent to 100% of the base metal strength), which represents a 50–100% increase in strength compared to joints without coating or filler metal. Fractographic microstructural studies also confirmed these results, showing that in the presence of filler metal, the fracture location shifted predominantly from the brittle intermetallic compound regions to the more ductile eutectic areas. This change in fracture mechanism reflects a significant improvement in joint quality and an increase in the service life of the produced joints
  9. Keywords:
  10. Intermetallic Compounds ; Aluminum ; Solid-Liquid Interface Anisotropy ; Aluminum-Copper Joint ; Copper ; Liquid–Liquid Interface ; Microstructural Refining

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