Effects of Alternating Cusp-Shaped Magnetic Field on Penetration Behavior, Microstructure, and Mechanical Properties in TIG Welding

This study investigates the effects of an alternating cusp-shaped magnetic field on the penetration behavior, microstructure, and mechanical properties of TIG-welded 304 stainless steel. Experimental results demonstrate that the applied magnetic field dynamically alters arc morphology through Lorentz forces, cyclically compressing or expanding the arc. This alteration leads to a reduced effective arc area on the workpiece, significantly enhancing penetration depth. At optimal parameters (25A excitation current, 200Hz frequency), the penetration depth increased to 3.55 mm, doubling compared to non-magnetic welding. Microstructural analysis revealed substantial grain refinement, with an average grain size reduction of 41% under the 25A magnetic field, alongside a weakened {001}<100>-cube texture, where the maximum pole density decreased from 8.10 to 3.13. The suppression of this texture, which is detrimental to tensile strength, is attributed to disrupted heat flow alignment and continuous oscillation-induced variations in the temperature field during solidification. Consequently, the tensile strength of welded joint improved to 777 MPa (99% of the base metal), primarily due to grain boundary strengthening and randomized grain orientation. These findings highlight the alternating cusp-shaped magnetic field as an effective method to enhance TIG welding efficiency by optimizing penetration and microstructure, providing insights into texture control and mechanical property enhancement in welded joints.