Tool-Pin Effects on Material Mixing and Strain Rates in FSW of Al-Cu Binary Alloy Plates

Joining of Al-Cu binary alloy (AA2219-T87) plates by friction stir welding (FSW) with optimum process and tool parameters would give minimal residual stresses and distortion with maximum weldment strength in contrast to the plasma-arc welding processes. The size and shape of the weld zone is influenced by the flow of plasticized material and the shear rate induced by rotating tool, which determine the FSW joint strength. Research groups have experimentally investigated on the effect of circular vs. flat tool-pin surfaces in friction stir butt welds of aluminum alloys, but a detailed discussion on the material flow with mixing as well as the shear rates was limited due to the challenges in measurements. In the present work, an Arbitrary-Lagrangian–Eulerian (ALE) model for the coupled thermal–mechanical-material flow phenomena has been developed to study the effect of FSW tool-pins (conical, triangular and square) on material flow and mixing pattern, strain rates and size of weld zones. The use of appropriate mesh element sizes near the tool-pin and away from it, an interfacial boundary conditions between plasticized-workpiece and rigid-tool materials as well as the selection of suitable solver would enhance the ALE model prediction accuracy. Upon comparison between the measured and predicted size of weld zones, a difference of about 5–7% was found, which is within the acceptable range.