Continuous wave-Nd: yttrium-aluminum-garnet laser welding of AM60B magnesium alloy

This study shows that the formation of macroporosity and overfill in the weld pool were the most pronounced problems during continuous wave Nd:yttrium-aluminum-garnet laser welding of AM60B die cast magnesium alloy. The influences of various welding parameters on the formation of porosity and overfill were investigated with particular emphasis on the mechanism and prevention of porosity formation. It was found that the macro pores in the weld pool were mainly formed by the expansion and coalescence of the preexisting pores in the base metal. The amount of macroporosity in the weld pool could be reduced to approximately that in the base metal by reducing heat input, i.e., by increasing welding speed and decreasing laser power. Increasing the beam defocusing did not reduce porosity in the weld metal until the beam was highly defocused and a shallow weld pool, characteristic of conduction mode welding was obtained. Overfill was observed for deep penetration autogenous welds and its formation could be attributed to porosity formation and the resulting displacement of the liquid metal over the top surface of the workpiece. (C) 2000 Laser Institute of America.