Friction stir welding (FSW) experiments were conducted using three different aluminium alloys (a work hardened alloy, an age hardened alloy and a cast alloy) followed by metallographic examination focusing on the upper weld zone and the surface layer. The examination has revealed the features of the major forward flow resulting from the forward motion of the tool shoulder. A thin shear layer due to tool rotation 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 welding, has suggested a dominant sliding contact condition.
Knowledge on the contact condition at the tool/workpiece interface is essential for
understanding many aspects of FSW. In the present study, FSW experiments were conducted using
aluminium alloys followed by metallographic examination focusing on the tool shoulder-workpiece
interface region. It was observed that an interfacial intermetallic layer and hence metallurgical
sticking/soldering readily formed. Temperature measurements have suggested the presence of
interface liquid, hence suggesting a mechanical sliding contact condition dominant. This has been
supported by the observation on material flow within the shear layer.
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.
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