Comparative Analysis of MIG Brazing Modes: Process Stability, Bead Morphology, Microstructure, and Mechanical Properties

Abstract

This study compares various modes of metal inert gas (MIG) brazing concerning process stability, bead morphology, microstructure, and mechanical properties. The pulsed-MIG process produces joints with flatter and wider bead morphology, indicating better wettability compared to cold metal transfer (CMT) and standard-MIG processes. This difference is due to the higher heat input of the pulsed-MIG process at the same wire feed rate (WFR). Analysis of voltage-current signals, probability distribution curves, and cyclograms reveals that the CMT-MIG process is the most stable and defect-free, while the standard-MIG process becomes less stable with increasing WFR. Joints brazed using the pulsed-MIG process have significantly higher shear-tensile strength compared to the other two modes, primarily due to higher wettability. Three modes of failure—horizontal interface (mode 1), vertical interface and bead (mode 2), and base metal (mode 3)—were observed. Excessive wettability reduces the cross-sectional area, negatively impacting static and dynamic performance, especially in pulsed brazing joints under high load amplitudes. Conversely, the bumpy beads in CMT and standard-MIG processes enhance the cross-sectional area, providing better resistance against failure along the vertical interface and bead. This study offers a comprehensive database and guidance for selecting appropriate brazing methods depending on joint application, considering the limitations of each brazing process.