In a significant scientific endeavour, Dr Maheshwar Dwivedy, Associate Professor in the Department of Mechanical Engineering, and Dr B Prasanna Nagasai, Post-Doctoral Researcher have jointly authored a research paper titled “Metallurgical Characteristics of AA6061 Aluminium and AZ31B Magnesium Dissimilar Joints by Fusion Welding Technique”. Their work delves into the metallurgical properties of dissimilar joints formed by fusion welding between AA6061 aluminium and AZ31B magnesium.

The study, published in the esteemed Q1 journal “Microscopy Research and Technique”, sheds light on the intricate interactions between these two dissimilar materials. By employing advanced microscopy techniques, the researchers meticulously examined the weld interfaces, grain structures, and elemental compositions. Their findings contribute to our understanding of the joining behaviour and intermetallic formation in such hybrid joints.

This collaborative effort exemplifies SRM University – AP’s commitment to cutting-edge research and interdisciplinary exploration. As the scientific community continues to unravel the mysteries of material behaviour, Dr Dwivedy and Dr Nagasai’s work stands as a beacon of knowledge and innovation.

Stay tuned for more updates on this groundbreaking research!

Abstract

Aluminium (Al) and magnesium (Mg) alloys are extensively used in the automobile sector because of their high strength-to-weight ratio, excellent castability, low density and simplicity of recycling. Al-Mg structures that automotive uses have a big chance of lowering their weight. Although there is a significant opportunity for substantial cost reduction, the use of magnesium in aluminium structures remains restricted. This study aims to weld 3 mm-thick rolled sheets of AA6061 Al and AZ31B Mg alloy using the cold metal transfer (CMT) arc welding process. Three different filler wires (ER1100, ER4043, and ER5356) were used in the experiment. In this article, the mechanical and microstructure characteristics of Al/Mg dissimilar joints manufactured by CMT are evaluated and discussed in depth. Optical microscope (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction were all used to analyse the CMT-welded Al/Mg dissimilar joints. Of the three filler wires used, ER4043 (Al-5%Si) filler wire yielded defect-free sound joints due to the presence of Si, which improves the flow ability of molten filler during welding. The Al/Mg dissimilar weld still produced the Mg-rich intermetallic (IM) Al12Mg17 and the Al-rich IM Al3Mg2. The surfaces of the fractured area of the CMT-welded Al/Mg dissimilar joints revealed the presence of the Mg-rich intermetallics (Al12Mg17), which is responsible for the decrease in tensile strength. The reduction of intermetallics, particularly of Mg-rich intermetallics (Al12Mg17) is important for improving joint strength.

Highlights

• Cold metal transfer (CMT) arc welding was used to control the Al-Mg-rich intermetallics in the Al/Mg dissimilar joints.
• The microstructure, morphology and phase composition of the welded joints were studied by OM, SEM, TEM, EDS and XRD.
• The weld metal and AL substrate are joined with a strong interface, while the weld metal and Mg substrate are joined with an epitaxial solidification area where the intermetallic compounds of Mg2Al3, Mg17Al12 and Mg2Si are generated.
• The weld metal on the Mg side experienced a brittle fracture, with a continuous distribution of Mg2Al3, Mg17Al12 and Mg2Si.

Explanation of Research in Layperson’s Terms

Al and Mg alloys are extensively used as light metals in engineering due to their advantageous characteristics, including high strength-to-weight ratio, cheap casting costs, low density, excellent machinability, and simple recyclability. Often, each of these materials fails to meet the criteria for lightweight buildings. Consequently, there is a high need for a significant quantity of Al/Mg hybrid structures in many industrial sectors with a particular emphasis on the automotive industry. Choosing the appropriate filler material for joining Al and Mg is crucial for creating robust weldments. The main difficulty in welding dissimilar metals like aluminium and magnesium lies in the formation of inflexible and brittle intermetallic compounds (IMCs) like Mg2Al3 and Mg17Al12, which severely affect the joint’s strength. When it comes to melting points, magnesium is at 650°C and aluminium is at 660°C. Based on the Mg-Al binary phase diagram, the compounds Mg2Al3 and Mg17Al12 can be produced at 450 and 437°C by eutectic reaction. Hence, the primary challenge in Al/Mg dissimilar welding is effectively suppressing the growing number of IMCs. Similarly, minimising energy input and utilising the appropriate chemistry of wire are the primary methods for decreasing the formation of IMCs and improving joint strength.

CMT is an advanced arc welding process which comes under controlled short circuiting transfer mode. The CMT welding cycle consists of two phases, i.e. the arcing phase and short circuit phase. In arcing phase, the filler wire gets melted and it forms as a droplet at the tip of the filler wire. In short circuiting phase, the droplet bridges the gap between the electrode and the weld pool. Once the short circuiting takes place, the filler wire gets retracted backward due to the retraction force and the droplet is detached from the filler wire. In conventional short circuiting transfer mode, the electromagnetic pinch force assists in detaching the droplet from the filler wire and thereby high heat input is produced by means of the short current. Where as in CMT short circuit transfer mode, the welding current is decreased to a lower value whenever a short circuit signal is sensed by the power source and the droplet gets separated from the filler wire with the help of the retraction force that is generated during the backward movement of the filler wire. Finally, the heat input is reduced to a lower value with this metal transfer mode. So, the CMT arc welding process was used to join the 3 mm-thick rolled sheets of AA6061 Al and AZ31B Mg alloy dissimilar materials. This article details the microstructural characteristics of an Al/Mg dissimilar joint. The CMT process controlled IMCs in the Al/Mg dissimilar joint and increased weld metal hardness compared to base metal.

The title of Research Paper in the Citation Format

aAddanki Ramaswamy, *aBellamkonda Prasanna Nagasai, aMaheshwar Dwivedy, Sudersanan Malarvizhi, Visvalingam Balasubramanian, Metallurgical Characteristics of AA6061 Aluminium and AZ31B Magnesium Dissimilar Joints by Fusion Welding Technique, Microscopy research and technique, 2024. DOI: 10.1002/JEMT.24510.
Corresponding Author: Bellamkonda Prasanna Nagasai

Collaborations

Dr. V. Balasubramanian, Professor & Director, Centre for Materials Joining & Research (CEMAJOR) Annamalai University, Annamalai Nagar-608002, Tamilnadu

Future Research Plans:

Planning to work on Fusion Welding (CMT, MIG, TIG, LASER, PLASMA and EBW) and Solid State Welding Processes (FSW, Rotary Friction Welding, Resistance Spot Welding, Magnetic Pulse Welding). Working on Additive Manufacturing (Wire Arc Additive Manufacturing on Metals, 3D Printing on Plastics), Cladding and Machinability. Characterisation, Tribology, and Corrosion. Steels and alloys, Aluminum, Nickel and Titanium Alloys.