Influence of process parameters on the physical and material properties of WAAM steels

Wire arc additive manufacturing (WAAM) is a metal 3D printing technique that offers the opportunity to fabricate large-scale structural components with high geometric flexibility and reduced material waste. This study aims to investigate the influence of different process parameters and cooling methods on the physical, mechanical and microstructural properties of WAAM steels with a view to assessing their suitability for use in construction. Six WAAM steel plates with nominal thicknesses of 3.5 mm, 5 mm, 8 mm and 12 mm, printed using ER90S-D2 welding wire, different process parameters and active or passive cooling, were examined. A total of 72 tensile coupons extracted at different orientations relative to the print layers with either as-built or machined surface conditions were tested. 3D laser scanning was performed to capture the as-built surface undulations and facilitate the calculation of surface roughness. X-ray computed tomography (XCT) scanning was conducted on selected coupon specimens to examine the printing defects. The tensile testing revealed that the WAAM steels exhibited largely isotropic elastic behaviour, which aligned with the weak crystallographic texture found in the microstructural analysis. The as-built geometry led to notable reductions in strength and ductility, particularly in as-built specimens loaded perpendicularly to the print layers. The results also showed that the thicker WAAM plates generally exhibited lower yield strength due mainly to the slower cooling rate leading to coarser grains, as revealed by the microstructural examinations. High porosity was observed in the XCT scan results of some coupons and was shown to significantly reduce the material ductility. Finally, the adopted active cooling method was found to increase productivity, but to have a minimal effect on the resulting mechanical properties. The presented findings contribute to the understanding of the material behaviour of WAAM steel and its link to the key process parameters. • The knowledge gap regarding links between process parameters and material properties of WAAM steels was addressed; • An experimental programme on WAAM carbon steels printed using ER90S-D2 welding wire was conducted; • Nominal wall thicknesses from 3.5–12 mm, produced using different process parameters and cooling methods, were examined; • Surface roughness and defects were investigated via 3D laser scanning and XCT scanning respectively; • Tensile coupon tests and microstructural analysis showed that thicker WAAM steels tended to exhibit lower yield strengths.