Thermal and solute diffusion in [formula omitted]-Mg dendrite growth of Mg-5wt.%Zn alloy: A phase-field study

Abstract

Thermal and solute diffusion plays an important role in α-Mg dendrite growth, the diffusion mechanism of which is still unclear. Here, thermal and solute diffusion in α-Mg dendrite growth of Mg-5wt.%Zn alloy under non-isothermal solidification were studied using the phase-field method. Results show that solidification latent heat will be concentrated at the dendrite intersection, which makes thermal field distribution non-uniform, and it is similar to the profile formed by connecting primary dendrite tips. The increase in temperature will shorten primary dendrite arms, reduce side-branching development, increase dendrite tip temperature, and decrease dendrite tip concentration stability. Moreover, solidification latent heat will first diffuse to undercooled melt, then diffuse to other areas, finally, system temperature tends to be unified. The variation range of concentration difference is very small in the solidification process, and solute field distribution is uniform all the time. The local high-concentration areas will be formed after the superposition of the solute enrichment layer, and solute atoms will first diffuse to undercooled melt through the solid-liquid interface, and then concentrate between side-branching and dendrites.