Abstract
The assistance of ultrasonic vibration during the friction stir welding (FSW) process has been verified as an effective approach for the improvement of joint strength. In the present study, experimentation on Al/Mg dissimilar alloys in butt joint configuration is implemented by employing FSW with and without the assistance of ultrasonic vibration. An optimized tool shoulder diameter of 12 mm is utilized, and the ultrasonic vibration is applied perpendicularly onto the tool along the welding direction, which is named UVaFSW. The results of joint appearance and macrostructure, characteristics of the intermetallic compounds (IMCs), as well as joint strength and fracture appearance are compared between Al/Mg FSW joints with and without ultrasonic vibration. It is demonstrated that the material intermixing between Al and Mg alloys is substantially strengthened in the UVaFSW joint compared with that in the FSW joint. Additionally, the ultrasonic vibration can be beneficial for the reduction of IMC thickness, as well as the formation of intermittently distributed IMC phases at the Al–Mg bonding interface. Consequently, the mechanical properties of Al/Mg FSW joints are significantly improved with the assistance of ultrasonic vibration. The maximum ultimate tensile strength is 206 MPa at tool rotation speed of 800 rpm and welding speed of 50 mm/min for the Al/Mg UVaFSW joint.
Highlights
For the purpose of environmental protection and energy saving, aluminum (Al) and magnesium (Mg) alloys have shown great potential in aerospace, automobile and railway transit industries as constituent parts of lightweight structures [1,2,3,4]
The results showed that the formation of less brittle Ni-based intermetallic compounds (IMCs) phases instead of Al12Mg17 could result in an improved tensile strength of the dissimilar Al/Mg friction stir welding (FSW) joint
It can be seen that the arc banded features are visible in both FSW and UVaFSW joints, and the surface perfection of FSW joint is improved with the assistance of ultrasonic vibration by visual impression from the figures without the filtering processing shown in Figure 3a,b for the joints of FSW and UVaFSW, respectively
Summary
For the purpose of environmental protection and energy saving, aluminum (Al) and magnesium (Mg) alloys have shown great potential in aerospace, automobile and railway transit industries as constituent parts of lightweight structures [1,2,3,4]. Numerous experimental studies in recent years have demonstrated that tool profile, tool rotation speed, welding speed and relative position of Al/Mg plates significantly influence on heat generation, plastic material flow and intermixing between Al and Mg, type of reaction at Al–Mg bonding interface, as well as macro-/microstructure and mechanical properties of the Al/Mg dissimilar FSW joint [1,4]. The ultrasonic vibration was found to be beneficial for the Al/Mg dissimilar FSW process, the maximum tensile strength of the Al/Mg dissimilar joint was limited to a value of ~178 MPa [33], which was relatively lower compared with that of the base material. The correlation of Al/Mg dissimilar FSW joint mechanical properties with macroscopic material intermixing and IMC distribution with and without ultrasonic vibration are discussed
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