Microstructures and mechanical behavior of aluminum-copper lap joints

Significance 

Aluminum-copper dissimilar joints are important structural components in a number of mechanical structures in metallurgical, chemistry, and electronic device systems. The Al-Cu joints offer the advantages of possessing high heat and electrical conductivities, and excellent corrosion resistance reference to the use of both copper and aluminum. However, the process of joining aluminum and copper is faced with a number of challenges owing to the large differences in the physical properties of aluminum and copper, and the formation of a fragile intermetallic compounds that deteriorate the mechanical integrity of the dissimilar joints.

Cold metal transfer method was developed from gas metal arc welding with low heat input to join aluminum and copper. However, there is an insufficient study focusing on the Al-Cu joints prepared by low heat input pulsed double electrode gas metal arc welding methods. It has been found that the intermetallic compounds generated in the aluminum-copper joints dictated the mechanical integrity as well as the durability of the joints. The intermetallic compounds are dependent on the amount of heat input in the joining process and the composition of the filler materials.

Therefore, accurate tuning of the heat input dictates the quality of the dissimilar joints with specific filler materials. Researchers at Lanzhou University of Technology and University of Kentucky and led by Professors Yu Shi and Fuqian Yang used a pulsed double electrode gas metal arc welding to join an aluminum alloy sheet to a copper sheet with an ER4047 filler wire. They studied, while controlling the heat input, the effects of the welding current on the shear strength and microstructures of Al-Cu joints. Their research work is published in peer-reviewed journal, Materials Science & Engineering A.

The authors joined 5052 aluminum alloys with pure copper implementing low heat input pulsed double-electrode gas metal arc welding brazing method using AlSi12 filler material. They then studied the effects of heat input on the mechanical characteristics and microstructure of the joints consisting of Al-Al welding zone and Al-Cu brazing zone.

The authors were able to precisely control the heat input into the base metal of copper. This allowed for the control of the formation of the intermetallic compounds and the microstructures of the lap joints. They observed that there were three zones in the Al-Cu lap joints. These were the fusion zone, weld metal zone, and the brazed interface zone. The brazed zone was majorly made of Al2Cu intermetallic compounds. The thickness of this layer increased with increasing welding current into the base copper metal.

Adopting the theory of thermal activation process, the authors derived a quadratic relation between the intermetallic layer thickness and the welding current intensity. Experimental findings supported this relationship and suggested that the electron wind force had a negligible effect on the Al2Cu intermetallic compounds layer growth.

The authors recorded an increase in the shear strength of the Al-Cu lap joints with increasing welding current. A maximum value of shear strength was recorded at 35 A welding current, and then begun to drop with increasing welding current owing to dispersion of Al2Cu intermetallic compounds of large sizes in the aluminum alloy.

The fracture surface was observed to vary with the welding current into the base copper metal, which was tuned by the microstructures generated during the pulsed double electrode gas metal arc welding brazing.

About the author

Professor Yu Shi is the dean of School of Materials Science and Technology, Lanzhou University of Technology, China

His research is mainly focused on advanced welding methods, welding physics, welding process control and some other fields. He has published more than 100 academic papers, including “Study on high efficiency MIG welding and its process and parameter model by by-pass coupled arc method”, “Study on MIG welding method and mechanism of double bypass coupling arc welding for aluminum-steel” and “Analysis of interaction between human and molten pool based on welder experience and study of optimal control method for molten pool flow”. His research has been supported by the National Natural Science Fund, the International Cooperation Project of the National Natural Science Fund, and the Ministry of Education Key Projects. His webpage is

About the author

Professor Fuqian Yang is a full professor in the Department of Chemical and Materials Engineering at the University of Kentucky. The primary goal of his research is to advance the understanding of the fundamental principles of the electrical-chemical-mechanical behavior of materials and to apply them to solve engineering problems.

Professor Yang has focused his research on the characterization and modeling of the mechanical behavior of lead-free alloys, nanostructured materials, and energy materials, on the contact deformation of small-volume structure, and on the effect of electromechanical interaction on the deformation behavior of materials. He places the emphases of applications on the use of nanoindentation and microindentation in determining the electrical-mechanical properties of materials at the micron and nano scales. 

Reference

Xianglong Zhou, Gang Zhang, Yu Shi, Ming Zhu, Fuqian Yang. Microstructures and mechanical behavior of aluminum-copper lap joints. Materials Science & Engineering A, volume 705 (2017), pages 105–113.

 

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