Arc instability in hybrid laser-GMAW welding process using Ni based filler wire NiCrMo-4

Abstract

NiCrMo-4 alloy, due to its excellent low-temperature properties and low ductile-to-brittle transition temperature, is widely used as a filler material for welding critical cryogenic structures such as large LNG storage tanks. However, the ER-NiCrMo-4 wire, with its high melting point, viscosity, and surface tension, tends to soften and exhibit irregular whipping at the wire tip during gas metal arc welding (GMAW) at currents far below the critical spray transfer current. This results in process instability and limits the application of GMAW in welding the inner tanks of LNG storage systems, where high safety and reliability are required. This study first investigates the instability mechanisms of ER-NiCrMo-4 wire during GMAW, and then examines the effects of laser assistance on droplet transfer behavior by analyzing the coupling between laser and arc plasma under different laser-wire distances. Results show that the laser can regulate the droplet transfer stability of ER-NiCrMo-4 wire, and arc stability is influenced by the degree of coupling between the laser and arc plasmas, as well as the competing effects of metal vapor reaction forces. When the laser-to-arc axial distance (D_LA) is set between 2 and 3 mm, a relatively stable arc is achieved.