Numerical study of dendrite coherency during equiaxed solidification by the Discrete Element Method

Equiaxed solidification of Al alloys has been simulated by a continuum model in 2D, producing morphology variations from near-globular to highly-branched dendritic. The resulting microstructures were taken as initial samples to perform direct-shear simulations using the Discrete Element Method (DEM) and study the dendrite coherency point. Crystal rearrangement in response to direct-shear is analysed in different grain morphologies with a focus on force transmission and crystal translations and rotations. The simulations show that the coherency point decreases significantly as the morphology becomes more dendritic. Significant rotation was observed around the shear plane, leading to local dilation. The modelling results reproduce the key trends reported in prior experiments on the effect of grain size and morphology on dendrite coherency, and suggest that the coherency point depends on both the internal fraction of liquid within the crystal envelopes and also on the shape of envelopes.