Copper and aluminum materials are extensively used in different industries because of its great conductivities and corrosion resistant nature. It is important to join dissimilar materials such as c...

A Review on Dissimilar Friction Stir Welding of Copper to Aluminum: Process, Properties, and Variants

Because joining dissimilar metals is often difficult by fusion joining, interest has been growing rapidly in using friction stir welding (FSW), which is considered a revolutionary solid-state welding process, as a new way to join dissimilar metals such as Al alloys to Mg alloys, Cu, and steels. Butt FSW of Al to Mg alloys has been studied frequently recently, but the basic issue of how the welding conditions affect the resultant joint strength still is not well understood. Using the widely used alloys 6061 Al and AZ31 Mg, the current study investigated the effect of the welding conditions, including the positions of Al and Mg with respect to the welding tool, the tool travel speed, and the tool rotation speed on the weld strength. Unlike previous studies, the current study (1) determined the heat input by both torque and temperature measurements during FSW, (2) used color metallography with Al, Mg, Al3Mg2, and Al12Mg17 all shown in different colors to reveal clearly the formation of intermetallic compounds and material flow in the stir zone, which are known to affect the joint strength significantly, and (3) determined the windows for travel and rotation speeds to optimize the joint strength for various material positions. The current study demonstrated clearly that the welding conditions affect the heat input, which in turn affects (1) the formation of intermetallics and even liquid and (2) material flow. Thus, the effect of welding conditions in Al-to-Mg butt FSW on the joint strength now can be explained.

Al-to-Mg Friction Stir Welding: Effect of Material Position, Travel Speed, and Rotation Speed

In dissimilar-metal friction stir welding (FSW), intermetallic compounds can form in the stir zone and significantly reduce the joint strength. The formation of intermetallic compounds in Al-to-Mg FSW was investigated in lap and butt FSW of the widely used 6061 Al and AZ31B Mg and discussed using the binary Al-Mg phase diagram as an approximation. Temperature measurements during lap FSW indicated a 703 K (430 °C) peak temperature, slightly below the eutectic reaction (Mg) + Al12Mg17 → L at 710 K (437 °C), because the thermocouples were pushed downward during welding. The intermetallic compounds in the stir zone were revealed by color etching and identified by X-ray diffraction (XRD), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM) as Al3Mg2 and Al12Mg17. Additional FSW was conducted near the edge of the upper sheet, and the liquid droplets squeezed out during welding solidified along the edge. Optical microscopy of the solidified droplets and EPMA revealed dendrites of Al3Mg2 and Al12Mg17 and interdendritic eutectics, thus indicating eutectic reactions (Mg) + Al12Mg17 → L (710 K (437 °C)) and (Al) + Al3Mg2 → L (723 K (450 °C)). Differential scanning calorimetry (DSC) confirmed that the solidified droplets melted at 709 K (436 °C) and 722 K (449 °C), nearly identical to the eutectic temperatures. Formation of intermetallic compounds on the order of 1 mm in size suggests they form upon solidification of the liquated material instead of solid-state diffusion.

Formation of Liquid and Intermetallics in Al-to-Mg Friction Stir Welding

At present aluminium-magnesium alloys are widely used in various engineering applications due to its light weight and superior properties. Joining is considered as one of the most complex phenomenon in various precision industries like aerospace, railway, automotive and marine structures because inflexible tolerances are required during different product assembly. The friction stir welding (FSW) of aluminium-magnesium of various grade has incited substantial scientific and industrial importance since it has a potency to transform the product with a good quality joint. The fabrication of such alloys is a challenging task through conventional fusion welding due to its various metallurgical concerns. Therefore, the present work is intended to summarize the recent progress in FSW of aluminium-magnesium alloys. Particular attention has been paid to microstructural evolution, phase transformation, recrystallization mechanism, material flow behaviour and how the process parameters influence the various mechanical properties and associated defects during FSW. Various experimental and numerical simulation results have been mentioned for weld property comparison. Finally, this work not only points out the prominent conclusions of the preceding research but also recommends the upcoming guidance concerning to fabrication of aluminium-magnesium alloys through FSW.

Recent research progress in solid state friction-stir welding of aluminium–magnesium alloys: a critical review

The aim of this investigation was to study material flow during dissimilar friction stir welding of AA 5083-H111 to deoxidised high phosphorus copper plates of 1 mm thickness. The welds were performed using different tool geometries and welding parameters. The positions of the copper and aluminium plates, relative to the advancing and retreating sides of the tool, were also changed. It was found that the tool geometry and relative position of the plates deeply influence the morphology of the aluminium and copper flow interaction zones, influencing the distribution of both materials in the weld and the formation of intermetallic compounds. The material accumulated under the tool during welding was found as another important aspect determining weld morphology.

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Material flow in heterogeneous friction stir welding of aluminium and copper thin sheets

The welding and joining of dissimilar metals which have very different properties, such as aluminium and carbon steel, is considered to be a subject for research and development in the welding/joining sector continuing into the 21st century. There are also huge requirements and expectations for this sector.1 Due to the aforementioned, the research and development of welding and joining of dissimilar materials have been carried out over many years; for instance, eutectic bonding of copper pipe and aluminium pipe was developed 30 years ago and this process is still applied for the heat pipes of refrigerators. Recently it has even progressed for applications in joining of wide plate materials of aluminium alloy and stainless steel by means of the vacuum rolling process2 and also for weldments of aluminium alloy and carbon steel joined by means of friction welding and employed as automobile components.3 However, there are problems from aspects of cost and restrictions concerning the configurations fo...

H Okamura

Papers

Joining of dissimilar materials with friction stir welding