Visualization of the material flow in AA2195 friction-stir welds using a marker insert technique

The material flow in solid-state, friction-stir, butt-welded AA2195-T8 was investigated using a marker insert technique (MIT). Markers made of AA5454-H32 were embedded in the path of the rotating friction stir welding (FSW) tool and their final position after welding was detected by metallographic means. Changes in material flow due to welding parameter and tool geometry variations were examined. The method provides a semiquantitative, three-dimensional view of the material transport in the welded zone. Because of the placement of markers at different positions at the weld centerline, the material transport in the longitudinal, transverse, and the vertical directions could be studied. Markers embedded in the path of the tool remain continuous after welding. The material transport, which is not symmetrical about the weld centerline, was such that the bulk of the material was transported to a position behind its original position, Superimposed on the primary motion of material in the horizontal plane of the weld is a circulation about the longitudinal axis of the weld. This circulation is found to increase with increasing weld energy.