Weld metal composition change during conduction mode laser welding of aluminum alloy 5182

Selective vaporization of volatile elements during laser welding of automot ive aluminum alloys affects weld metal composition and properties. An exper imental and theoretical study was carried out to seek a quantitative unders tanding of the influences of various welding variables on vaporization and composition change during conduction mode laser welding of aluminum alloy 5 182. A comprehensive model for the calculation of vaporization rate and wel d metal composition change was developed based on the principles of transpo rt phenomena, kinetics, and thermodynamics. The calculations showed that th e vaporization was concentrated in a small high-temperature region under th e laser beam where the local vapor pressure exceeded the ambient pressure. The convective vapor flux driven by the pressure gradient was much higher t han the diffusive vapor flux driven by the concentration gradient. The comp uted weld pool geometry, vaporization rates, and composition changes for di fferent welding conditions agreed well with the corresponding experimental data. The good agreement demonstrates that the comprehensive model can serv e as a basis for the quantitative understanding of the influences of variou s welding variables on the heat transfer, fluid flow and vaporization occur ring during conduction mode laser welding of automotive aluminum alloys.