In laser keyhole welding of alloys, low meltingpointelements, such as aluminum or magnesium, canbe easily vaporized and lost from the weld region,leading to the changes of composition, mechanicalproperties, and the susceptibility of hard cracking andother defects. In hybrid laser-MIG keyhole welding,compositions of the base metal and filler metal areusually different, allowing some "anti-crack" elementsto be added through the filler metal in anticipation ofreducing or eliminating the aforementioned problems.Apparently, in order to achieve the desired objectives,it is a prerequisite to have good mixing between thebase metal and filler metal in the molten pool. Hence,it is very important to know how well the mixingbetween the base metal and fill metal would be andwhat parameters are controlling the mixingphenomena.In this study, mathematical models and theassociated numerical techniques have been developedto investigate the mixing process in both spot and 3-Dmoving hybrid laser-MIG keyhole welding. Thedynamics of the weld pool fluid flow and theinteractions between droplets and weld pool arecalculated as a function of time. The effects of dropletsize (wire diameter), droplet frequency (wire feedspeed), welding speed, and the distance between theMIG and laser beam on weld pool mixing are studied.It is found that the competition between the rate ofmixing and the rate of solidification determines thecompositional homogeneity of the weld pool.Parameters that can influence either the rate of mixingor the rate of solidification or both are investigated anddiscussed.
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