Application of thermal modelling to laser beam welding of aluminium alloys

Abstract

A thermal model has been developed for laser welding which describes the heat input in terms of point and line sources. The model was used to generate weld profiles which closely matched those found by experiment. Outputs of the model (the thermal gradient G_L and the growth rate R) were used to describe the macroscopic grain structure found along the weld centreline. Columnar structures were predicted at low welding speeds (high G_L/R ratio) and equiaxed structures at high welding speeds (low GL/R ratio). Using the thermal model, cooling rates of ～1500 K s^–1 were estimated for the lowest welding speed, which increased by an order of magnitude for the highest welding speed considered. There was excellent agreement between the dendrite secondary arm spacings measured by experiment and those predicted using the thermal model.