Experimental and numerical investigation of copper–steel cold metal transfer wire arc additive manufacturing

This study presents an integrated experimental and numerical investigation of a CuAl8–ER70S-6 bimetallic structure fabricated by Cold Metal Transfer (CMT) Wire Arc Additive Manufacturing (WAAM). The work aims to assess microstructural evolution, interfacial characteristics, and distortion mechanisms in multi-material WAAM while developing a computational framework to predict bead geometry and thermo-mechanical deformation. Bimetallic tower specimens were produced using a controlled snail-pattern deposition strategy and characterised using high advanced microscopy. The CuAl8 region showed cellular–dendritic solidification with directional grain growth governed by steep thermal gradients, whereas ER70S-6 exhibited a mixed columnar-equiaxed ferritic microstructure driven by cyclic reheating. At the interface, a narrow dilution zone with limited Cu–Fe mixing was observed, without brittle intermetallic compounds, confirming effective heat input control using CMT. EDS and EBSD results indicated asymmetric diffusion, with deeper Fe penetration into CuAl8 and shallow copper enrichment within the steel. To capture process-induced distortion, a hybrid analytical-FEM approach was implemented to estimate bead geometry and simulate thermal fields and residual stresses. The model predicted bead flattening, layer curvature, and an inverted-frustum distortion profile consistent with experiments. The results confirm the feasibility of CMT-WAAM for copper–steel structures and validate the proposed simulation strategy effectively.