Study on the Weldability of Copper-304L Stainless Steel Dissimilar Joint Performed by Robotic Gas Tungsten Arc Welding

Andrei Mitru; Augustin Semenescu; George Simion; Elena Scutelnicu; Ionelia Voiculescu

doi:10.3390/ma15165535

Study on the Weldability of Copper-304L Stainless Steel Dissimilar Joint Performed by Robotic Gas Tungsten Arc Welding

Materials (Basel). 2022 Aug 11;15(16):5535. doi: 10.3390/ma15165535.

Authors

Andrei Mitru^{1

2}, Augustin Semenescu^{1

3}, George Simion⁴, Elena Scutelnicu⁴, Ionelia Voiculescu⁵

Affiliations

¹ Faculty of Materials Science and Engineering, Politehnica University of Bucharest, 313 Splaiul Independentei St., 060042 Bucharest, Romania.
² National Research and Development Institute for Gas Turbines COMOTI, 220 D Iuliu Maniu Bvd., 061126 Bucharest, Romania.
³ Academy of Romanian Scientists, 3 Ilfov, 050044 Bucharest, Romania.
⁴ Faculty of Engineering, "Dunarea de Jos" University of Galati, 800008 Galati, Romania.
⁵ Faculty of Industrial Engineering and Robotics, Politehnica University of Bucharest, 313 Splaiul Independentei St., 060042 Bucharest, Romania.

Abstract

The welding process of dissimilar metals, with distinct chemical, physical, thermal, and structural properties, needs to be studied and treated with special attention. The main objectives of this research were to investigate the weldability of the dissimilar joint made between the 99.95% Cu pipe and the 304L stainless steel plate by robotic Gas Tungsten Arc Welding (GTAW), without filler metal and without preheating of materials, and to find the optimum welding regime. Based on repeated adjustments of the main process parameters-welding speed, oscillation frequency, pulse frequency, main welding current, pulse current, and decrease time of welding current at the process end-it was determined the optimum process and, further, it was possible to carry out joints free of cracks and porosity, with full penetration, proper compactness, and sealing properties, that ensure safety in operating conditions. The microstructure analysis revealed the fusion zone as a multi-element alloy with preponderant participation of Cu that has resulted from mixing the non-ferrous elements and iron. Globular Cu- or Fe-rich compounds were developed during welding, being detected by Scanning Electron Microscope (SEM). Moreover, the Energy Dispersive X-ray Analysis (EDAX) recorded the existence of a narrow double mixing zone formed at the interface between the fusion zone and the 304L stainless steel that contains about 66 wt.% Fe, 18 wt.% Cr, 8 wt.% Cu, and 4 wt.% Ni. Due to the formation of Fe-, Cr-, and Ni-rich compounds, a hardness increase up to 127 HV_0.2 was noticed in the fusion zone, in comparison with the copper material, where the average measured microhardness was 82 HV_0.2. The optimization of the robotic welding regime was carried out sequentially, by adjusting the parameters values, and, further, by analyzing the effects of welding on the geometry and on the appearance of the weld bead. Finally, employing the optimum welding regime-14 cm/min welding speed, 125 A main current, 100 A pulse current, 2.84 Hz oscillation frequency, and 5 Hz pulse frequency-appropriate dissimilar joints, without imperfections, were achieved.

Keywords: EDAX chemical composition; SEM microstructure; dissimilar joint; microhardness; robotic Gas Tungsten Arc Welding.

Grants and funding

This research received no external funding.