MATERIAL FLOW IN THE UPPER WELD ZONE DURING FRICTION STIR WELDING.

Friction stir welding (FSW) experiments were conducted, using a work hardened aluminium alloy and a cast aluminium alloy followed by examination focusing on the upper weld zone. The examination has revealed the feature of the major forward flow due to the forward motion of the shoulder. A thin shear layer was identified between the tool shoulder and the workpiece with a distinctive shear flow direction. The thickness of the shear layer was alloy dependent. An embedded layer in the upper weld zone has also been identified. The flow phenomena leading to this will be discussed. A velocity profile in the shear layer, based on the apparent alignment of Si particles in the cast alloy after FSW, has suggested a dominant sliding contact condition. [ABSTRACT FROM AUTHOR]