Mitru Andrei, Semenescu Augustin, Simion George, Scutelnicu Elena, Voiculescu Ionelia
Faculty of Materials Science and Engineering, Politehnica University of Bucharest, 313 Splaiul Independentei St., 060042 Bucharest, Romania.
National Research and Development Institute for Gas Turbines COMOTI, 220 D Iuliu Maniu Bvd., 061126 Bucharest, Romania.
Materials (Basel). 2022 Aug 11;15(16):5535. doi: 10.3390/ma15165535.
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 was noticed in the fusion zone, in comparison with the copper material, where the average measured microhardness was 82 HV. 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.
具有不同化学、物理、热学和结构特性的异种金属焊接工艺，需要进行专门研究并予以特别关注。本研究的主要目的是通过机器人钨极气体保护电弧焊（GTAW），在不使用填充金属且不对材料进行预热的情况下，研究99.95%铜管材与304L不锈钢板材之间异种接头的可焊性，并找出最佳焊接规范。基于对主要工艺参数（焊接速度、摆动频率、脉冲频率、主焊接电流、脉冲电流以及焊接结束时焊接电流的下降时间）的反复调整，确定了最佳工艺，进而能够实现无裂纹和气孔、全熔透、致密性良好且具备密封性能的接头，确保在运行条件下的安全性。微观结构分析表明，熔合区是一种多元素合金，由于有色金属元素与铁的混合，铜在其中占主导地位。焊接过程中形成了富含铜或铁的球状化合物，通过扫描电子显微镜（SEM）检测到这些化合物。此外，能量色散X射线分析（EDAX）记录了在熔合区与304L不锈钢界面处形成的一个狭窄的双混合区的存在，该区域含有约66 wt.%的铁、18 wt.%的铬、8 wt.%的铜和4 wt.%的镍。由于形成了富含铁、铬和镍 的化合物，与铜材料相比，熔合区的硬度增加到了127 HV，铜材料的平均测量显微硬度为82 HV。通过依次调整参数值，进一步分析焊接对焊缝几何形状和外观的影响，实现了机器人焊接规范的优化。最后，采用最佳焊接规范（焊接速度14 cm/min、主电流125 A、脉冲电流100 A、摆动频率2.84 Hz和脉冲频率5 Hz），获得了无缺陷的合适异种接头。
