Three-dimensional modeling of grain structure evolution during welding of an aluminum alloy

Abstract

The structure and properties of welded and additively manufactured alloys are affected by the microstructural evolution in the fusion zone (FZ) and heat affected zone (HAZ). The motion of the liquid pool and the interdependence of grain growth in both the solid and liquid regions are important in the evolution of the final grain structure. Previous investigations of microstructure evolution have been limited to either the HAZ or the FZ and in many cases in idealized isothermal systems. Here we report the evolution of grain structure and topology in three dimensions in both the FZ and the HAZ considering the motion of the liquid pool. Temporal and spatial distributions of temperature obtained from a well-tested heat transfer and liquid metal flow calculation are combined with Monte Carlo and topology calculations in a computationally efficient manner. The computed results are tested against independent experimental data for arc welding of an aluminum alloy. The average size of the columnar grains in the FZ and the equiaxed grains in the HAZ are shown to decrease with increasing scanning speed. For a given weld, the size and aspect ratio of the columnar grains in the longitudinal and horizontal planes are shown to decrease with distance from the weld interface. It is further shown that the grain size distributions and topological class distributions in the HAZ are largely unaffected by the temporal and spatial variations of the temperature created by different welding parameters.