Effect of wire feed rate on ER70S-6 microstructure of wire arc additive manufacturing process

This study investigates the manufacturing and characterization of ER70S-6 single line-wire arc additive manufacturing (WAAM) using a cobot to produce defect-free samples. Adjusting the wire feed rate aims to improve efficiency in fabricating steel frames for building structures. In this regard, 1-mm-diameter ER70S-6 wire samples were fabricated with feeder rates ranging from 4.5 to 6.5 m/min, maintaining a constant robot speed of 7 m/min. The voltage and current of the WAAM machine were controlled between 14.8–16 V and 125–159 A, respectively. Microhardness profiles and grain sizes at grain dilution of the area were systematically compared to monitor the solidification behavior after the process. Electron backscatter diffraction (EBSD) analysis assessed the crystallographic orientations and calculated the grain sizes. Optical microscopy and scanning electron microscopy (SEM) revealed uniform, defect-free surfaces of metal mixing during the WAAM process in the 100 ± 10 µm upper than dilution area. As a result of two types of cooling processes following WAAM, transferring heat into the substrate and environment, the formation of Widmanstätten ferrite on top of the beads’ peaks was more extensive. The grain size in the middle of the bead ranged from approximately 8.6 to 11.6 µm, while at the dilution area, it decreased to 3 to 5.6 µm. This variation influenced the microhardness, which reached 300 ± 15 HV.