Material flow and mechanical properties on friction stir lap welds of Alclad AA2024 sheet

Abstract

The material flow pattern, especially the flow pattern of the thin pure aluminum clad layer on Alclad 2024 sheet in a friction stir lap weld is crucial to the joint quality. It was interesting to observe that the thin clad layer at lap interface did not scattered in the stir zone after friction stir welding. It remained intractable in the form of a continuous layer in the stir zone despite of a complete penetration of the probe into the upper and lower sheets. By using cylindrical and sector-shape threaded probes, the thin aluminum clad layer can be effectively broken, scattered or deformed in the stir zone. In addition to the flow pattern of the clad layer, the hook formation at clad layer end near the stir zone boundary together with the effective sheet thickness (EST) of the upper sheet also played an important role in the fracture modes and the tensile strength of the FSW lap joint of Alclad 2014 aluminum. Investigation on the macro- and microstructure of the stir zone and its adjacent area allows an interpretation of the tensile performance of the lap joint associated with the material flow patterns and tool geometries.