Study of viscous layer in friction welding of Fe/Al dissimilar metals: Formation, evolution and effect on joint properties

Abstract

In friction welding of aluminum alloys to steel, an interlayer consisting of thermoplastic metal is formed at the interface. However, the current research on this interlayer is still insufficient. In this paper, two different welding control methods are designed using self-developed welding equipment, the control method of “Rotating and Separating after welding” and the control method of “Stopping immediately after welding”. Rotary friction welding of aluminum alloys to steel has been investigated by combining the two control methods. The results show that in rotary friction welding of aluminum alloys to steel, an interlayer consisting of thermoplastic aluminum is formed at the interface, which is called the viscous layer. The formation and evolution of the viscous layer are summarized and quantified by comparing the interface morphology obtained at different times and by different control methods. It was found that the viscous layer first formed at the 1/2–2/3 position of the friction interface, then spread across the interface and finally covered the entire friction interface. At the same time, the interface friction state was changed due to the formation of the viscous layer. The interface friction gradually changed from Coulomb friction between aluminum alloy and steel to adhesive friction between aluminum alloy and viscous layer. It was also found that the viscous layer had an important contribution to the formation of welded joints. The coverage area of the viscous layer, the metallurgical reaction between the viscous layer and the steel, and the microstructure of the viscous layer are the main factors affecting the strength of the joint.