Electrical conductivity field analysis: A prognostic instrument for real time monitoring of friction stir welding process

Abstract

Constant monitoring of manufacturing processes is crucial for ensuring high-quality products and cost-effectiveness. Non-destructive testing (NDT) techniques, such as eddy current testing (ECT), offer a direct and accurate means of evaluating weld quality in real-time. ECT can assess microstructural changes in welded materials by measuring electrical conductivity. Establishing a robust correlation between electrical conductivity and microstructural changes induced by FSW process parameters remains a critical step to bridge existing knowledge gaps. In this study, electrical conductivity field analysis using eddy currents was conducted on AA6082-T6 FSW joints. A pivotal factor controlling process heat input and influencing defect formation and weld microstructural features is the ratios of FSW tool rotational speed (ω) to travel speed (v). Previous works often evaluated only one set of process parameters, while our study examines multiple combinations of ω and welding speed v to develop a more robust correlation between electrical conductivity and microstructural changes. Both defective and defect-free joints were obtained employing various ω/v ratio and electrical conductivity results were compared with hardness measurements and tensile test results. The analysis reveals a consistent trend between electrical conductivity variations, microstructural changes in weld zones, and microhardness as the ω/ν ratio varies. Our findings show that, at a constant travel speed, an increasing ω/ν ratio is associated with enhanced microhardness and decreased electrical conductivity, attributed to grain refinement. Conversely, at a constant rotational speed, a higher ω/ν ratio leads to increased electrical conductivity, due to the enhanced dissolution of strengthening precipitates. Furthermore, analyzing electrical conductivity profiles and identifying local maxima corresponding to weld failure zones could strengthen the correlation. This approach suggests the potential to assess variations in mechanical properties resulting from process drift, specifically influenced by changes in the ω/v parameter over time. Microstructural analysis through electrical conductivity evaluation emerges as a valuable and predictive tool for assessing weld properties, with promising applications in process monitoring.