Abstract
Friction stir welding (FSW) experiments were conducted using three different aluminium alloys (a workhardened alloy, an age hardened alloy and a cast alloy) followed by metallographic examination focusingon the upper weld zone and the surface layer. The examination has revealed the features of the majorforward flow resulting from the forward motion of the tool shoulder. A thin shear layer due to tool rotationwas identified between the tool shoulder and the workpiece with a distinctive shear flow direction. Thethickness of the shear layer was alloy dependent. An embedded layer in the upper weld zone has also beenidentified. The flow phenomena leading to this will be discussed. A velocity profile in the shear layer, basedon the apparent alignment of Si particles in the cast alloy after welding, has suggested a dominant slidingcontact condition.
