Achieving a stable arc is a major challenge in dissimilar metal corner welding during the fabrication of aerospace engines. However, severe arc deflection occurs during arc initiation and stabilization. In this study, the arc deflection mechanisms were revealed in dissimilar nickel/stainless steel gas tungsten arc welding (GTAW) corner joints based on welding experimental observations and numerical simulations. At arc initiation, two separate molten pools were formed on the base metals; the arc deflected toward the nickel side, because the higher electrical conductivity of nickel made it more favorable for initial current transfer and arc attachment along the shortest arc path. As welding proceeded, a common molten pool was formed; the electrical conductivity difference inside the molten pool was diminished, while thermal effects became dominant. Because stainless steel has a lower thermal conductivity than nickel, the steel side reached a higher surface temperature and experienced stronger metal evaporation, which enhanced plasma conductivity and promoted arc deflection toward the steel side. The weld showed an asymmetric morphology with undercut at the nickel-side weld toe and near burn-through on the steel side. Compared with the 90° corner joint, the 120° corner joint exhibited more concentrated temperature and current density near the root, weaker arc deflection, less weld asymmetry, and better weld formation. These results provide a useful reference for understanding arc deflection in dissimilar corner-joint welding using GTAW and for optimizing the welding process.

The engine thrust chamber, which consists of an electroformed nickel (Ni) outer wall and a copper-zirconium alloy (Cu-Zr alloy) inner wall, is widely used in the aerospace field. With regenerative cooling technology, the Cu-Zr alloy wall is milled with grooves through which the low-temperature fuels of liquid hydrogen and oxygen can flow to absorb heat in the chamber. When joining the thrust chamber with other parts by arc welding, the Ni/Cu-Zr alloy interfacial bonding strength decreases because of the high temperature, and large welding stress may occur at the interface, resulting in debonding. In this study, the interfacial bonding strength between the electroformed Ni and the Cu-Zr alloy was measured at different temperatures, and the thermal and mechanical processes of the Ni/Cu-Zr alloy interface during welding with different parameters were investigated by numerical simulation. Tensile test results show that the Ni/Cu-Zr alloy interfacial bonding strength decreases significantly with the increase in temperature, resulting from the microstructural deterioration of the Cu layer at the interface. The model calculation results show that the interface temperature exceeds 700 degrees C due to the welding heat input, and a significant stress concentration occurs on Cu-Zr alloy rib edges near the weld, leading to debonding. Reducing welding power and adjusting welding speed may result in insufficient Ni penetration, and the debonding tendency still exists. It is found that precisely adjusting the welding heat input while enhancing the inner wall heat conduction by a water-cooling fixture can prevent the Ni/Cu-Zr alloy interface from debonding and ensure the weld quality.

Segregation affects the solute content within the grains, as well as the content and distribution of the secondary phases at grain boundaries, leading to structural and property inhomogeneity. It also influences the microstructure evolution during the remelting and post-heating in directed energy deposition-arc (DED-Arc), ultimately impacting product performance in both as-built and heat-treated states. In this study, a 2219 aluminum alloy wall was fabricated using DED-Arc. Numerical simulation was employed to calculate the temperature field of the additive manufacturing process and solidification parameters. The segregation behavior and microstructure characteristics were analyzed. Both macrosegregation and microsegregation were observed in the as-built wall. Within a single layer, the Cu content is higher at the top where the metal solidifies last, than at the bottom where it solidifies first. The microsegregation is more severe in the first few layers due to the higher cooling rate. As the DED-Arc process progresses, eutectics enriched in the interlayer form a reticular network due to remelting, while a finer grain size is achieved through Cu enrichment and Al3Zr nucleants. As the layer-by-layer deposition process continues, the as-built wall alternates between coarse-grained unmelted intralayers, coarse-grained partially remelted intralayers with network-distributed eutectics, fine-grained remelted interlayers with network-distributed eutectics and fine-grained newly deposited interlayers.

采用拉伸试验测量了电铸镍/锆铜高温下和经过热循环后的结合强度,利用扫描电子显微镜对断口表面形貌和经过高温或热循环后的试样组织进行观察.结果表明:经过高温后,电铸镍、电铸铜发生回复再结晶,晶粒由沿电铸方向的柱状晶转变为等轴晶,组织均匀化.电铸铜晶粒随温度升高长大.随着拉伸温度升高,电铸镍/锆铜结合强度下降,试样由穿晶断裂转变为沿晶断裂.经历最高温度在400℃及以下的热循环后,试样室温结合强度有小幅上升;经历最高温度在500℃及以上的热循环后,试样室温结合强度小幅下降.

针对航天发动机钢套与推力室搭接角接头焊接问题,开展了 GH4169与纯镍异种材料TIG焊搭接角接头的焊接工艺试验,分析了不同焊接参数对接头成形质量及力学性能的影响.研究结果表明:搭接角接头外观质量良好,GH4169侧熔合较好,镍侧熔深较浅.焊接电流主要影响镍侧熔深,焊接速度主要影响镍侧熔宽、焊缝截面尺寸及接头力学性能.接头强度与镍侧熔宽线性相关,强度较低时拉伸试样断裂于焊缝内部,强度较高时断裂于晶粒粗化的镍侧热影响区.分析得到了拉伸力与焊接电流、焊接速度、送丝速度的关系式,总结了满足接头成形及性能良好的焊接参数条件域.

ER2319 welding wires were used to fabricate a wall structure using CMT-PAdv-based wire and arc additive manufacturing (WAAM). Heat treatment was used after the WAAM process. The microstructure and mechanical property anisotropy before and after the heat treatment were studied. There were three areas with different grain morphology along building direction in the as-deposited wall structure. Microstructure difference was clear between interlayer regions and intra-layer regions both in as-deposited and heat-treated state. Netlike second phases became discontinuous after heat treatment, but pores and Fe-rich phases basically unchanged. Mechanical property presented isotropy before heat treatment because α-Al with lower Cu content had low resistance on crack initiation or growth and crack mainly grew via netlike second phases which had no directionality. Mechanical property presented anisotropy after heat treatment because α-Al was strengthened and brittle Fe-rich phases which concentrated in interlayer regions played a leading role in crack initiation. Moreover, the tensile loading force along the building direction was perpendicular to interlayer regions. Thus, mechanical properties in building direction were lower than that in deposition direction.