Abstract
Laser beam welding is a widely used joining process in industrial application. Within the
process a highly inhomogeneous temperature field in the joined materials is generated,
which causes changes in mechanical properties, residual stresses and component distortion.
The high temperatures in the liquid pool and in the heat-affected zone lead to a
severe change in material microstructure. The mechanical properties depend strongly
on the microstructure and change therefore dramatically in the fusion- and heat-affected
zone compared to the properties in the base material.
This work determines the residual stress field in a butt joined, precipitation hardened
aluminum alloy via a phenomenological continuum model. The material behavior is
defined by a thermomechanical material model, which changes the behavior from viscoplastic
below the solidus temperature to a pure viscous behavior above the liquidus
temperature. A mixed finite element formulation is used to ensure incompressible
material behavior above the melting temperature. The temperature field is described
based on the heat conduction equation in combination with a three-dimensional Gaussian
power distribution. The temperature field is solved by a semi analytical solution which
utilizes the method of Greens- Functions. As a consequence of the severe change
of mechanical properties based on the dissolution of precipitations a kinetic model is
used, which describes the dissolution of precipitations. Residual stresses of butt welded
specimens are measured with synchrotron x-rays and compared with the numerically
determined stress fields.
