Effect of self-induced magnetic field on liquid flow and segregation during VAR process for titanium alloys
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摘要: 采用合金凝固的连续介质模型，模拟了钛合金真空自耗电弧熔炼过程中温度场、溶质场、流场、自感电磁场的演化行为。通过对比浮力单独作用、自感电磁力单独作用以及二者共同作用下的熔池流动及成分偏析结果，揭示了熔炼过程中熔体流动和溶质偏析的形成机理。结果表明，0.3 kA小电流熔炼时，熔池内熔体流动由浮力主导，形成侧壁向下、中心向上的对流；0.73 kA大电流熔炼时，熔池内呈现由电磁力主导的反向对流，熔池最大流速为0.036 m/s；0.45 kA中等电流熔炼时，浮力和电磁力对熔体流动的作用均比较明显，熔池内形成两个流动方向相反的区域，且由于两者相互竞争制约，导致熔池中最大流速达到极低值0.004 m/s。铸锭整体宏观成分偏析随着熔炼电流的增加呈现先上升后下降再上升的变化规律，三阶段宏观偏析的极值分别为0.54%、0.39%与0.57%。当电磁力和浮力作用基本相当时，宏观偏析程度最轻。Abstract: A continuum model for alloy solidification was used to simulate the temperature evolution, solute distribution, liquid flow, and self-induced magnetic field during VAR process for titanium alloys. The work reveals the influence of self-induced magnetic force and/or buoyancy force on the melt flow and solute segregation by contrastively exerting the forces. When a small melting current of 0.3 kA is used, the melt flow is dominantly driven by the buoyancy force that the melt flows downward at the side of the melt pool and upward in the center of the melt pool. When a large melting current of 0.73 kA is used, the melt flow is dominantly driven by the self-induced magnetic force and the melt flows adversely, and the maximum velocity reaches 0.036 m/s. When a medium current of 0.45 kA is applied, both the two forces act evidently, forming two regions in the pool where the melt flow directions are opposite, and the maximum flow rate in the pool can reach a minimum value of 0.004 m/s due to their competition. With increasing the current, the total segregation of the ingot rises at begin, has a reduction stage after a peak, but then increase continuously again. The extreme values of the three stages are 0.54%, 0.39% and 0.57%, correspondingly. The minimum segregation can be obtained when the self-induced magnetic force and buoyancy force act equally.
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Key words:
- titanium alloy /
- vacuum arc remelting /
- continuum model /
- self-induced magnetic field /
- liquid flow /
- macrosegregation
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图 1 VAR过程磁通密度绝对值|B|和洛伦兹力F随时间的演化，每个时刻中左图为|B|分布，右图为F分布
Figure 1. The absolute value of the magnetic flux density (|B|, left) and Lorentz force vector (F, right) evolution with time during VAR process
图 2 不同熔炼电流下（从左往右），浮力与洛伦兹力单独作用及耦合作用下（从上往下）温度场与流场分布，每幅图左半边为温度场、右半边为熔池轮廓和流场
Figure 2. Temperature distribution and melt flow under different current with buoyancy force and/or Lorentz force
图 3 不同熔炼电流下浮力与电磁力综合作用下熔池内温度场和流场分布
Figure 3. Distribution of temperature field and flow field driven by buoyancy and Lorentz force with different remelting current
图 4 熔池内最大流速及熔池深度随熔炼电流的变化规律
Figure 4. The maximum velocity in molten pool and pool depth with different remelting current
图 5 0.45 kA电流熔炼过程中溶质分布随时间演化，每幅图右侧为耦合流场及熔池轮廓
Figure 5. The concentration evolution with time during the 0.45 kA current remelting process, coupled flow field and pool’s profile on the right side of each picture
图 6 0.3 kA (a)与0.73 kA (b)下熔炼到达最大高度时的流场与偏析
Figure 6. Solute distribution and melt flow when the ingot reaches a maximum height using 0.3 kA(a) and 0.73 kA(b)
表 1 计算模型采用的物性参数[13]
Table 1. Physical parameters of the computational model
密度 / （kg·m−3） 扩散系数 / (m2·s−1) 熔化潜热 / (J·kg−1) V分配
系数液相线斜率 / (K·%−1) 热膨胀系
数 / %−1比热容 / (J·kg−1·K−1) 热导率 / (W·m−1·K−1) 流体粘度/ (kg·m−1·s−1) 电导率 / (S·m−1) 磁导率 / (H·m−1) 4170 4.0×10−9 3.77×105 0.95 −2.0 −0.35 975 32.7 3.1×10−3 1.0×106 1.26×10−6 
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