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利用定量相场模型,以Mg-0.5 wt.%Al合金为例模拟了基面((0001)面)内镁基合金的等温自由枝晶生长过程.通过研究该合金体系数值模拟的收敛性,获得了最优化值耦合参数λ=5.5及网格宽度△x/W_0=0.4,并在该参数下系统研究了各向异性强度和过饱和度对枝晶尖端生长速度、尖端曲率半径、Peclet数及稳定性常数σ~*的影响.结果表明,由微观可解性理论得到的稳定性系数σ~*与ε_6拟合值σ~*∝ε_6~(1.81905),更接近理想值σ~*(ε_6)∝ε_6~(1.75).此外,当过饱和度Ω<0.6时,稳定性系数σ~*不随ε_6的变化而变化,而当Ω>0.6时,稳定性系数σ~*随着ε_6的增加而减小.这反映了枝晶的生长由扩散控制向动力学控制的转变.随着过饱和度的增加,枝晶形貌由雪花状枝晶向圆状枝晶转变.
By using the model of quantitative phase field, the isothermal free-dendrite growth process of Mg-0.5 wt.% Al alloy in the base (0001) plane was simulated. By studying the convergence of numerical simulation of the alloy system, The optimized coupling parameter λ = 5.5 and the grid width Δx / W_0 = 0.4 were obtained. Under this parameter, the effects of anisotropy intensity and supersaturation on the growth rate of tip dendrites, tip radius of curvature, Peclet number And the stability constant σ ~ *. The results show that the stability coefficient σ ~ * and ε_6 fitting value σ ~ * αε_6 ~ (1.81905) obtained by the theory of microscopic releasability are closer to the ideal value σ ~ * ( In addition, when the degree of supersaturation Ω <0.6, the stability coefficient σ ~ * does not change with the change of ε_6, while when Ω> 0.6, the stability coefficient σ ~ * increases with ε_6 Which reflects the change of dendrite growth from diffusion control to kinetic control.With the increase of supersaturation, the dendrite morphology changes from snowflake dendrite to circular dendrite.