Wire and arc additive manufacturing (WAAM) produces thin-walled parts superior to other additive manufacturing methods, because of its high efficiency, good compactability, and low cost. However, the WAAM accuracy is limited by its large heat input. Here, 0.8 mm 316L stainless steel welding wire is deposited via speed cold welding to form 30-layered thin-walled samples, with 2 mm thickness, and up to 65 mm height. The effects of three process parameters (the bottom current mode, scanning speed, and cooling time) on the deposition process stability, macro morphology, structure, and mechanical properties are studied. In the experiment, the probability density curves of electrical parameters of sample #GRBC-30 cm/min-10 s on the third and tenth layers were narrower than other samples, which implied a more stable process. The three process parameters mainly affect the deposition morphology and have a minor performance effect. The hardness and tensile properties mainly depend on the deposition direction. Gradual, layer-by-layer current reduction improves the bottom molding and performance, and the deposition efficiency, and stabilizes the process. Scanning speed enhancement or cooling time reduction destabilizes the end formation, reduces the effective deposition rate, and slightly degrades the performance. All deposited samples are distinctly anisotropic, but satisfy the industrial standard. Overall, deposition in speed cold welding mode, with 10 s cooling time, 30 cm/min scanning speed, and gradually reduced bottom current exhibits good stability, and the molding efficiency and mechanical properties are optimal.

Wire and arc additive manufacturing (WAAM) has advantages of high efficiency and low cost. However, different welding current processes lead to different heat input and repeated heating treatment during the deposition process, which has an influence on the forming and performance. In this study, 30 layers of reciprocating depositions for 316L stainless steel were carried out by speed cold and speed arc welding processes, and the morphology, effective deposition rate per power, microstructure, and properties of depositions were compared. The outcomes indicated that different welding current processes make different shaping appearances, and the effective deposition rate per power of speed cold welding is 15.2% higher than that of speed arc welding. The microstructures of depositions are columnar crystals; however, the higher power of speed arc welding leads to the coarse structure, and the enhanced thermal cycle and preheating effect produce a uniform hardness and 4.9% higher tensile strength, but lower toughness than those of speed cold welding. Due to the direction of deposition, the tensile strength of depositions by two processes has obvious anisotropy that can reach to 8.18% and 13.3%, respectively.

The cold metal transfer plus pulse (CMT + P) process was performed to produce a 316L vertical wall through the single-channel multi-layer deposition method. The microstructure of different regions on deposited samples was observed by an optical microscope and a scanning electron microscope (SEM). The phase composition of the as-deposited wall was checked by X-ray diffraction, and the element distribution in the structure was analyzed by an energy-dispersive spectrometer. The tensile strength and microhardness of samples were tested, and the fracture morphology was observed by an SEM. Finally, the electrochemical corrosion characteristics of the as-deposited wall in different regions along the building direction were tested. Results from the experiments indicated that the microstructure of metallography showed a layer band. The metallurgical bounding between layers was carried out by dendrite remelting and epitaxial growth. Along the building direction, the alloy of different regions solidified in an ferritic-austenitic (FA) manner, and due to having undergone different heat histories, their SEM microstructures were significantly distinct. The ultimate tensile strength (UTS) and yield strength (YS) of the vertical specimens were higher than those of the horizontal specimens, displaying obvious anisotropy. Due to a large amount of precipitation of precipitated phases in terms of intermetallic compounds in the middle and upper regions, the tensile strength and microhardness along the building direction showed a trend of first decreasing and then increasing. In the bottom region, a small amount of ferrite precipitated in the austenite matrix, while in the middle of the as-deposited wall, the amount of ferrite gradually increased and was distributed in the austenite matrix as a network. However, due to the heat accumulation effect, the ferrite dissolved into austenite in large quantities and the austenite showed an obvious increase in size in the top region. A stable passivation film was caused by a relatively low dislocation density and grain boundary number, and the middle region of the arc as-deposited wall had the best corrosion resistance. The large consumption of chromium (Cr) atoms and material stripping in the top region resulted in the integrity of the passivation film in this region being the weakest, resulting in the lowest corrosion resistance.