Abstract
In the present paper, an attempt has been made to link friction stir welding (FSW) process control and response variables. Substantial similarities among the relationships between torque, nugget grain size, x axis force and tool rotation rate have been elucidated for three different aluminium alloys. Comparison of the experimental work to results from process simulation indicates that in each case a temperature limit is reached above some critical value of tool rotation rate. A simple method of estimating the strain and strain rate in friction stir welds is presented. The flow stress during FSW is calculated from measured torque values and analysed with respect to aluminium alloy flow stresses measured in standard, high temperature torsion and tensile tests. Results indicate that perhaps either sticking friction conditions are not always applicable during FSW (on all or part of the tool) or that, above a critical tool rotation rate, intermittently lubricated contact is present due to local melting in the weld process zone.