Effect of backward median current on stability, microstructure and mechanical properties of SUS304 weldments fabricated by local dry underwater MIG welding

Abstract

Abstract Local dry underwater backward median pulse MIG welding (LDU-BMPMIG) was proposed in this study. The effects of different backward median currents on welding process stability, weld forming, microstructure, and mechanical properties of weldments were investigated comprehensively. The results reveal that the backward median current waveform effectively improved the welding stability. With the increase of backward median current, the welding stability increased first and then decreased. With the backward median current of 200 A, the welding process stability was the most satisfied. The quality of weld formation was consistent with welding stability. LDU-BMPMIG weldments exhibited fewer macroscopic defects and better overall morphology compared with LDU-PMIG weldment. The weldment microstructure was mainly composed of γ-austenite and δ-ferrite with different morphologies. The satisfied stability of the welding process contributed to improving the microstructure uniformity. The variation trend of tensile strength for LDU-BMPMIG weldments was approximately kept consistent with welding process stability. The weldment prepared by 200A showed considerable mechanical properties with minimal fluctuation, which reached 97.5% of maximum average tensile strength, which meant the most excellent compared to the others. The experimental results can improve the stability of local dry underwater welding and provide a theoretical basis and technical support for the application of underwater welding.