稳态磁场辅助对激光熔凝层表面波纹的抑制作用研究

Suppression Effect of a Steady Magnetic Field on Surface Undulation During Laser Remelting

利用稳态磁场辅助激光熔凝,在不改变激光工艺参数的条件下,抑制了熔凝层表面的波纹。同时,建立了考虑熔池内部的传热、对流、相变、电磁力和熔池表面形貌的多物理场耦合仿真模型。通过对比实验结果讨论了在稳态磁场作用下,熔凝层熔池内部温度场和流场的变化规律以及表面波纹的抑制原理。结果显示,稳态磁场所提供的洛伦兹力为抑制熔池对流的阻力,其方向与熔池对流方向时刻相反。随着磁场强度的增加,熔池内部的整体流速逐渐降低,但温度场的变化不甚明显。当稳态磁场的强度大于0.5 T时,熔池形状发生变化,熔凝层表面的波纹高度明显降低,但金相组织基本不变。

A steady magnetic field is applied to suppress the surface undulation after laser remelting without changing the laser processing parameters. A two dimensional （2D） transient multi-physics numerical model, concerning heat transfer, fluid dynamics, phase transition, electromagnetic field and the surface morphology of molten pool, is established. Comparing with the experimental results and numerical results, the suppressing mechanism of surface undulation related to the temperature field and velocity field in the molten pool is discussed. The results indicate that the Lorenz force supported by the steady magnetic field is a sort of drag force, whose direction is opposite to the melt flow all the time. With increasing the magnetic flux density, the velocity of molten pool is reduced gradually, while the temperature field remains changeless. When the magnetic flux density is higher than 0.5 T, the shape of molten pool is changed and the height of surface undulation is decreased obviously without changing the microstructure.