Optimization of CMT-WAAM process parameters to minimize the porosity and surface roughness in bimetallic wall of aluminium alloys

Porosity and surface roughness are significant challenges that occur during the fabrication of aluminium alloy components via wire arc additive manufacturing (WAAM), as they directly affect the mechanical and structural properties of the final product and thereby make it essential to minimize these issues. In this study, the Taguchi technique is employed to optimize three key process parameters that significantly influence the reduction of porosity and surface roughness: current for ER5356 wire (I_ER5), current for ER4043 wire (I_ER4), and travel speed (TS). These parameters are further involved in the fabrication of bimetallic walls of aluminium alloys (ER5356/ER4043) using cold metal transfer-based WAAM. Results from the Taguchi method revealed the optimal parameters for fabricating the final wall as 115 A for I_ER5, 90 A for I_ER4, and 6 mm/s for TS. ANOVA further indicated that I_ER5 had the most significant effect on porosity and surface roughness, followed by I_ER4 and TS. Microstructural analysis of the wall at optimum parameters displayed a heterogeneous structure characterized by coarse equiaxed grains in the ER4043 layer, finer grains in the ER5356 layer, and a mix of fine equiaxed and columnar grains at the interface layer. Energy-dispersive spectroscopy (EDS) analysis showed significant differences in Si and Mg weight percentages at the interface. ER5356 layer exhibited the highest hardness (76.88 HV), which is 9.75% and 18.02% higher than the interface layer (70.05 HV) and ER4043 layer (65.14 HV). The interface layer displayed better strength with a value of 185.52 MPa and 16.64% elongation, having a ductile fracture mode marked by dimples and voids.