Numerical analysis of the dwell phase in friction stir welding and comparison with experimental data

Finite element modelling of material flow is used to understand physical phenomena occurring during the dwell phase of friction stir welding (FSW) of thin sheets made of 7075 aluminium alloy. Numerical results are compared to reference experimental data including torque measurements and metallographic observations made at different tool rotational speeds. The effects of the material constitutive parameters and the heat transfer coefficient between the welded sheet and the anvil backing are identified. The model is also used to study the contact at the tool/workpiece interface. Comparison between the experimental and calculated torques shows that the contact condition depends on tool rotational speed. This result is supported by the differences between nugget grain size and nugget shape evolutions obtained with different rotational speed.