The microstructure and corrosion resistance of samples fabricated by Q345 and 308 bimetallic feedings using two kinds of processes of wire-arc additive manufacturing (WAAM) was observed and compared with that of sample manufactured by a single feeding wire of Q345 or 308. The results show that the interface between the Q345 and 308 had no defects and metallurgical bonding. The hardness of bimetal Q345/308 additive manufacturing samples was higher than that of Q345 or 308 single wire additive manufacturing. The sample made of Q345 single wire had serious electrochemical corrosion, while the sample made of 308 single wire had pitting corrosion. The pitting corrosion of the sample reinforced by bimetal Q345/308 feeding wires was improved.

In this work, an Inconel 625 thin-wall structure was fabricated by the gas tungsten arc welding (GTAW) hot-wire arc additive manufacturing process. The microstructure and mechanical properties of the Inconel 625 samples, extracted from different orientations and locations of the thin-wall structure, were investigated and compared. The results showed that the additively manufactured Inconel 625 component, made by hot-wire GTAW, had good quality. Its microstructure consisted of dendrites, equiaxial crystals, and cellular crystals. The average hardness from the bottom to the top was similar, indicating that the thin wall had good consistency. The plasticity in the deposition direction was better than those in the other three regions, which was related to the dendritic structure in the sedimentary direction.

Because low thermal conductivity and high viscosity are common characteristics of austenitic steel, it is easy to cause a large amount of heat accumulation in the chip area, resulting in tool edge collapse or wear, and the traditional preparation method is unsuitable for preparing large and complex austenitic steel components. Wire + arc additive manufacturing (WAAM) provides a great application value for austenitic stainless steel because it can solve this problem. The cold metal transfer (CMT)-WAAM system with good control of heat input was used to fabricate the multi-trace and multilayer stainless steel 321 (SS 321) workpiece in this study. The microstructure and corrosion properties of the SS 321 workpiece were observed and compared with those of an SS 321 sheet. The results showed that the microstructure of the SS 321 workpiece from top to bottom was regularly and periodically repeated from the overlapping remelting zone, inter-layer remelting zone, and primary melting zone. There was white austenite matrix and black ferrite, and a small amount of skeleton and worm ferrite was distributed on the white austenite matrix. The average hardness value from the top to the bottom region was approximately uniform, indicating that the workpiece had good consistency. The corrosion properties in 0.5 mol/L H₂SO₄ solutions were compared between the SS 321 workpiece and the SS 321 sheet. The results showed that the corrosion properties of the top region of the workpiece were better than that of the middle and bottom part, and the corrosion properties of the SS 321 workpiece were better than that of the SS 321 sheet.

In this study, CoCrFeMnNiW medium-entropy alloy coating on Q235 was fabricated by plasma surfacing technology. The wear performance of the prepared one-layer coating and the two-layer coating was studied by a friction and abrasion tester. The microstructure and performance of the CoCrFeMnNiW coating were researched by optical microscope, a nano-indentation test, SEM, and hardness tester. The results show that the microstructure of the coating is made up of a fusion zone, equiaxed dendrites near the fusion zone, coarse columnar crystals, and near-surface with a certain direction between the near-fusion zone and near-surface fine equiaxed grains. The wear mechanism of one layer coating was abrasive with wear and fatigue wear. The wear mechanism of the two-layer coating was adhesive with wear and fatigue wear. For CoCrFeMnNiW MEA coating, the main factors determining their wear resistance were the value of its depth recovery ratio (η_h) and EIT.

Plasma arc welding (PAW)-cable-type seven-wire GMAW (gas metal arc welding) hybrid welding is known as a high-efficiency welding combining plasma arc, GMAW arc and cable-type welding wire. In this study, numerical simulation via Fluent of the molten pool temperature field and flow field and experimental verification were conducted on Q235 thin plate hybrid welding with cable-type wire to explore molten pool fluid behavior. The simulation results show that keyholes form in the molten pool due to the strong penetration ability of a plasma arc and then the evolved pores by the surface tension float out of the molten pool. When the GMAW welding current increases, both the length and width of the weld pool enlarge, the weld reinforcement increases and the flow rate of molten metal in the weld pool also speeds up. While the PAW current increases, the weld pool length also increases and the molten metal in the weld pool significantly flows faster, but the weld reinforcement decreases. When the welding speed increases, the weld pool length and fusion depth decrease, but the reinforcement will first increase and then decrease. The experimental results are in strong agreement with the simulation results. It shows that the numerical analysis model established in this paper is accurate, laying a certain theoretical foundation for the popularization of PAW-cable-type seven-wire GMAW hybrid welding.