Effectiveness and efficiency of tool alignment and simultaneity factors on double-sided friction stir welding for joining heat-treatable aluminum alloys: a review

Friction stir welding (FSW) can be challenging for joining thick heat-treatable aluminum alloy plates due to limitations with the single-pass method and heat distribution. To address these challenges, the double-sided FSW (DS-FSW) method was developed. It allows for welding the unwelded side of the plate which cannot be reached by the pin’s height at the first pass. DS-FSW has been proven to overcome many challenges and has been found to be a great solution for FSW in welding thicker plates. During DS-FSW implementation, some drawbacks related to machine parameters were discovered but were addressed through tool development. However, the time efficiency issue was only solved when two identical tools were used. This approach, known as simultaneous DS-FSW (SDS-FSW), significantly reduced processing time. It also led to improved microstructures and mechanical properties based on survey results. The dual-tool simultaneity provided flexibility for dwelling into the workpiece in different ways, such as parallel side-by-side, tandem in-line, and staggered transverse, which were mostly used for lap welding in single-pass FSW and showed remarkable performance. Regardless of the dwelling method used, the impact of process parameters in FSW must always be taken into consideration, emphasizing the importance of the tool profile and machine-related parameters being in optimal working order.