Study on in-situ material flow behaviour during friction stir welding via a novel material tracing technology

A novel material tracing technology was proposed using ER2319 aluminium alloy welding wire as the tracer material to study the material flow behaviour at different positions of friction stir welded 6061-T6 aluminium alloy joint. Having been influenced by temperature and driving force of the tool, the displacement of all the tracer materials deposited behind the original position during welding decreased gradually from top to bottom of the stir zone (SZ). The advancing side (AS) and the retreating side (RS) of the SZ are dominated by the shear action and the extrusion action, respectively. The extrusion force and friction force are the driving forces for material flow during friction stir welding. The material flowed downward at the AS and upward at the RS in the vertical plane of the joint, while the material of the SZ flowed to the back of the tool through the RS in all the horizontal planes of the joint. The flow path of tracer material in most positions of the SZ is arc shaped, however, it is a complex curve in the SZ bottom at the AS due to the poor material flowability. The rotation angle of the tracer material decreased from AS to RS of the SZ and from top to bottom of the SZ.