Laser beam welding of deoxidized copper: microstructure investigation and thermodynamic consideration

During the deep-penetration welding of phosphorus deoxidized copper, a multitude of reactions occur which influence the formation of phases inside the welding region. Thereby, the microstructure evolution during laser beam welding depends on the chemical composition of the alloy as well as of the gaseous environment. As a result of reactions in a phosphorus rich copper melt, copper phosphides are formed which are located inside the grains as well as at the grain boundaries. Meanwhile, the formation of phosphorus pentoxide and an uncomplete decomposition of copper-I-oxide to elemental copper and phosphorus pentoxide were identified at the keyhole. Thereby, the decomposition of copper-I-oxide depends on the oxygen concentration. Thus, a complete decomposition of copper-I-oxide to elemental copper and phosphorus pentoxide was observed at the bottom side of the welding region due to a higher oxygen concentration.