Process envelope and void defect analysis in FSW of AA2024, AA5052 and AA7075 aluminium alloys

This article investigates void defect formation in friction stir welding (FSW) of AA2024, AA5052 and AA7075. A total of 159 bead-on-plate welds were performed with real-time monitoring of temperature, force and spindle power. Travel speeds from 25 to 500 mm/min and tool rotation speeds from 300 to 1500 RPM were investigated. Process maps identified critical parameter ranges for different void defects. A new method was proposed to estimate torque from spindle power. Results show that high temperatures ( $>0.7T_{\mathrm{solidus}}$ ) are necessary but not sufficient for defect-free welds. Torque thresholds can distinguish cavity from tunnel and groove defects, while power input below 1000 W (AA2024) or 1050 W(AA7075) is generally necessary and sufficient to avoid voids. These findings enable real-time defect monitoring and process optimisation in FSW.