Impact of depositional direction and current on microstructure and mechanical properties of the bimetallic wall of ER5356/ER4043 fabricated by cold metal transfer based wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is increasingly gaining attraction from researchers and industries worldwide due to its low cost and the ability to produce intricate parts in a shorter time. In this study, the bimetallic wall of aluminium alloys (ER5356/ER4043) is fabricated by cold metal transfer based WAAM technique using two deposition directions (unidirectional and bidirectional) and three current combinations (115 A/90 A, 120 A/95 A, 125 A/100 A). The effect of deposition direction and current on microstructure evolution, mechanical properties, and residual stress has been investigated. Experimental results displayed better properties in bi-directional wall build at a current combination of 115 A/90 A. This is confirmed by optical microstructure as well as field emission scanning electron microscopy, which shows equiaxed grains on the ER4043 layer, fine grains on the ER5356 layer, and columnar-fine grains at the interface of the bi-directional wall while discontinuous dendritic grains is displayed in ER5356 layer of unidirectional wall. Energy dispersive spectroscopy analysis indicates a main difference in weight percentage for Si and Mg contents at the interface layer of the bidirectional wall than the unidirectional wall, with X-ray diffraction analysis specifying the intermetallic compounds like α-Al, Al₁₂Mg₁₇, Mg₂Si, AlMg, and Al_3.21Si_0.47 in both depositional directions. Tensile strength at the interface layer of the bi-directional wall surpasses the tensile strength of the unidirectional wall's interface layer, with fracture morphology indicating ductile fracture in all specimens. The microhardness test reveals an increase in hardness in the transverse direction at the current combination of 115 A/90 A and also in the bidirectional deposition wall compared to the unidirectional wall. Bidirectional deposition has generated less residual stress than unidirectional walls.