Quantitative phase-field simulation of dendrite growth in rapidly solidifying WE43 magnesium alloy

In the additive manufacturing of magnesium alloys, layer-by-layer melting and rapid cooling are the core process characteristics; the solute trapping and drag effects significantly influence dendrite growth and final microstructure. This study develops a quantitative phase-field model incorporating a modified anti-solute trapping term that is decoupled from the interface width to investigate the solute drag, temperature gradient ( G ), pulling velocity ( V p ), and sixfold-symmetric anisotropy intensity in dendrite growth during rapid directional solidification of WE43 magnesium alloy. Results show that complete solute drag reduces the peak solute concentration between dendrites by approximately 30%, effectively mitigating microsegregation and delaying morphological instability of the flat interface. Increasing G and V p drives a microstructural transition from dendritic to cellular crystals, causing the dendrite growth direction to shift from the preferential crystallographic orientation toward the heat flux direction, such that the growth angle θ decreases monotonically. As the anisotropy intensity increases, secondary dendrite arms nucleate earlier and side branches become more developed; this effect is particularly pronounced under low temperature gradients. A clear relationship exists between the primary dendrite arm spacing λ d and the process parameters: λ d ∝ G − 1 / 2 V p − 1 / 4 . High temperature gradients enhance directional heat conduction, while high pulling velocity increase interfacial undercooling and reduce the thickness of the solute diffusion boundary layer; together, these factors promote refinement of the dendrite array. This study elucidates the intrinsic mechanisms of dendrite growth under rapid solidification conditions and provides a theoretical basis for precise microstructural design in magnesium alloy additive manufacturing.