Increased quality and welding efficiency of laser butt welding of 2205/X65 bimetallic sheets with a lagging MIG arc

Abstract

2205/X65 bimetallic sheets were butt welded by a fiber laser with single pass based on flow behavior of molten pool in full penetration welding processes. Optimal welding parameters were defined based on experiments using orthogonal arrays design to ensure highest relative independence of the upper and lower fusion zones (FZ). Balance of ferrite and austenite was found to be completely disrupted. To counterbalance excess α-ferrite formed in the lower fusion zone, laser-Metal Inert Gas (MIG) tandem welding was introduced for butt welding of 2205/X65 bimetallic sheets. Microstructures and corrosion properties of welded joints were investigated using optical microscopy, scanning electron microscopy (SEM) and potentiodynamic tests. Metallographic observations indicated that MIG arc followed the rear of laser beam reheated the laser weld in the front. This resulted in increased austenite nucleation and growth in the FZ region of the flyer layer. Thermal power of MIG arc and laser arc distance were important factors, which affected grain size and alloy element content in ferrite and austenite. Potentiodynamic tests indicated that the FZ consists of fine grains with increased corrosion resistance, which was close to the parent metal exposed to chloride solution.