Experimental study of friction taper plug welding for low alloy structure steel: Welding process, defects, microstructures and mechanical properties

• Defect-free 25 mm deep welds are made by friction taper plug welding (FTPW).
• FTPW process and relationships between welding parameters are studied.
• Hardness distribution and microstructures of the welds are investigated.
• Tensile properties and fracture mechanisms for FTPW joints are discussed.
• Process parameter influence on weld qualities and mechanical properties are studied.

A research investigation has been undertaken to identify the various stages and variation of welding parameters in friction taper plug welding (FTPW) process and to explore their effects on the performance and properties of the welds. According to the variation of axial force, the overall FTPW process is divided into feeding phase, pressing phase, welding phase, and forging phase. The rotating speed, welding force, and burn-off rate remain nearly constant in welding phase. However, the torque peaks in welding phase when after few seconds of welding force setting is reached. Rising the welding force would increase the peak torque, welding torque, and burn-off rate, but decrease the welding time. When improper welding parameter is used lack of bonding and incomplete filling defects would form within the weld. The microstructure of the weld metal is consist of retained austenite, pearlite, and various Widmanstätten ferrite. In heat affect zone, it is mainly of lathy upper bainite. Defect free welds exhibit favorable tensile properties of which 548.3 MPa tensile strength and 27.5% elongation that equal to the base metal could be found.