The effects of welding parameters on the small scale resistance spot weldability of Ti-1Al-1Mn thin foils

• It is feasible to weld Ti-1Al-1Mn thin foils with SSRSW, the average welded joint strength was 65% of base material.
• The softening was discovered in heat affected zone (HAZ), because of pronounced grain growth.
• The peak load was observed to increase with increasing welding current, electrode force and with decreasing ramp time.
• The welding and holding time have virtually no effect on peak load, however which determine average grain size in HAZ.
• The peak load depended on weld nugget size and failure mode, while grain size effect also played an important role.

The present paper primarily investigates the effects of key welding parameters, including ramp time, holding time, welding time, welding current and electrode force, on small scale resistance spot weldability of Ti-1Al-1Mn thin foils with thickness of 0.05 mm. A single lap joint is performed to estimate mechanical properties of welded joint by tensile-shear test, together with weld morphology, microstructure, microhardness and element distribution examines. Weld morphology examine results demonstrate that diameter and thickness of surface indentation stabilize around 365 μm, 8 μm respectively. The variations of weld morphology with welding parameters differ significantly from large scale resistance spot welding (LSRSW). Microhardness examine results reveal that weld nugget has the highest microhardness value, and softening phenomenon is observed in heat affected zone (HAZ) with respect to base material, which is attributed to pronounced grain growth. Additionally, grain size effect becomes significantly as T/dg (sheet thickness to average grain size in HAZ) ratio below a critical value around 7. In light of obtained results, it could be validated that peak load of welded joint is mainly determined by weld nugget size, failure mode and average grain size of HAZ.

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