Design and Performance Evaluation of a FSW Tool for Welding of AW 7075-T651 Aluminum Alloy

Friction stir welding (FSW) is a solid-state joining process capable of producing high-quality joints in materials that are difficult to weld, particularly lightweight alloys. It is especially suitable for high-strength aluminum alloys like AW7075-T651, which are prone to hot cracking and mechanical degradation during conventional fusion welding. The AW7075-T651 alloy is one of the strongest commercially available aluminum alloys, whose high strength is primarily provided by MgZn2 precipitates. The influence of welding parameters, especially welding speed, on heat input was studied using thermocouples positioned beneath the tool shoulder and in the weld root region. Tool lifetime was evaluated using WC-Co probes with different Co content, while tool wear was analyzed by 3D scanning. Microstructural characterization was performed using EBSD and TEM analyses. The maximum tool lifetime reached 2.7 km. Welding speed significantly affected the temperature in the weld root region, and a minimum temperature of 0.58TM was required to produce a sound weld. Weld efficiency of 90% was reached; microhardness profiles showed a typical W-shape. TEM and SAED analyses confirmed the presence of an α-Al matrix and strengthening MgZn2 precipitates and showed a more uniform distribution and refinement of precipitates in the stir zone.