Single pass hybrid laser–MIG welding of 4-mm thick copper without preheating

• For the first time, hybrid laser–arc welding is used in copper joining process.
• Butt welding of 4-mm copper is achieved at high speed and without preheating.
• Defect-free joint is obtained in butt-joint configuration with a right gap size.
• Laser–MIG hybrid welding is a feasible, efficient welding method for copper.

Laser–arc hybrid welding of highly reflective T2 copper was conducted and significant synergy effect was observed. Effects of primary welding parameters on the shape and integrity of copper joints were studied through bead-on-plate (BOP) welding test. Results of X-ray inspection and infrared photography showed that both porosity susceptibility and crack susceptibility were highly dependent on welding heat input or energy coupling efficiency, but had totally different trend, which narrowed the process window of BOP welding of copper. Hot crack and porosity were successfully suppressed by using a square butt joint configuration with a proper gap size. A 4-mm thick, defect-free butt joint was obtained by single-pass hybrid welding at a speed of 1.3 m/min without preheating the work piece. The microstructure, microhardness, mechanical properties and tensile fracture surface of the butt joint obtained were studied. Tensile strength and elongation rate of the butt joint obtained were about 87% and 56% of that of base metal, respectively. The lowered mechanical properties of butt welded copper joint were related to the softening of fusion zone (FZ) and its vicinity, the coarse microstructure in FZ and heat affected zone (HAZ), and the possible concentration of impurity elements at the central region of FZ.

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