Effect of oscillating arc motion in pulsed arc GMAW-WAAM: a multi-aspect study of additively manufactured AM70 high-strength low-alloy steel

This study investigates the influence of oscillating arc motion during pulsed arc GMAW-WAAM (gas metal arc welding-based wire arc additive manufacturing) on the microstructural, crystallographic, and mechanical properties of AM70 HSLA (high-strength low-alloy) steel walls. Samples fabricated with and without torch oscillation are examined across different height zones and build orientations. Microstructural analysis using optical and scanning electron microscopy reveals finer and more homogeneous acicular ferrite and bainite structures in walls fabricated with torch oscillation, while energy-dispersive spectroscopy indicates more uniform manganese and nickel distribution. X-ray diffraction analysis confirms a consistent ferritic phase, stronger α-Fe (ferrite) peak intensities, and smaller crystallite sizes in oscillated samples. Residual stress analysis using the sin2ψ method shows higher compressive stress throughout the walls fabricated with torch oscillation. Mechanical testing reveals improved and more uniform hardness, enhanced yield and tensile strength (up to 526 MPa and 816 MPa, respectively), and fracture surfaces with fine, ductile features. A slight reduction in elongation and orientation-dependent variations in impact toughness are observed, with up to 12% improvement in the vertical direction. These findings highlight the role of torch oscillation in promoting thermal uniformity and process stability, contributing to improved structural performance in WAAM-fabricated AM70 steel components.