Effect of Welding Time on Microstructure and Mechanical Properties of Rotary Friction Weld Joints of AA6061

This study conducted an experiment to investigate the metallurgical and mechanical properties of joints made through rotary friction welding (RFW) using AA6061 aluminum alloy rods. The examination of the microstructures in the RFW joints was carried out by employing optical microscopy, along with observing the weld macrostructure using a low magnification microscopy to examine the flow behavior during the RFW process. Subsequently, the characterizations of RFW joints were conducted using Vickers microhardness measurements, tensile tests and fatigue tests using a rotating bending machine in combination with fractographic study. It was discovered that the higher welding time led to improved strength of the AA6061 weld joints but accompanied by the formation of more flashes and higher burn-off length. In contrast, at a low welding time, typically 5 s, the RFW process was inadequate to produce the friction heat required to make sound weld joint hence resulting in low strength. It appeared that the most satisfactory weld joint was achieved at 10 s welding time as indicated by its high strength, around 223.2 MPa with less flash was produced compared to the weld at the welding time of 15 s. This particular RFW joint had the fatigue strength lower than that of AA6061 base metal and the fatigue crack origin was located at the HAZ of AA6061 owing to softening during the welding process.