纵向强磁场对定向凝固Al-4．5％Cu合金显微组织的影响

EFFECT OF HIGH LONGITUDINAL MAGNETIC FIELD ON THE MICROSTRUCTURE OF DIRECTIONALLY SOLIDIFIED Al-4.5%Cu ALLOY

强磁场可明显影响Al-4．5％Cu(质量分数)合金定向凝固组织,在温度梯度G_T=38 K／cm,生长速率较低(R=5μm／s)时,10 T强磁场使液-固界面处的树枝晶变得不规则,低于共晶温度以下的固相区定向枝晶组织消失,组织细化；在生长速率R=50 μm／s时,10 T强磁场使得枝晶沿与凝固方向成一定角度定向排列,X射线衍射表明(111)方向转向磁场方向；在生长速率较高(R=100 μm／s)的情况下,10 T强磁场使得枝晶粗化,一次枝晶间距增大,从热电磁流体理论和磁晶的各向异性角度分析了上述现象。

An investigation of the microstructure of directionally solidified hypoeutectic Al- 4.5%Cu （mass fraction） alloys under a longitudinal magnetic field of 10 T showed that the field has a great influence on the dendritic arrays. The field caused severe distortion of the dendritic array morphology in the mushy zone and the directional dendrites disappeared below the eutectic isotherm at lower growth speed of R=5 μm/s, opposed to the well-aligned dendritic crystals in the absence of the field. At the growth speed of R=50 μm/s and a temperature gradient of 38 K/cm in the liquid, the alignment structure formed and the crystal （111） direction turned to the direction of the magnetic field, opposed to the dendrite growth along the crystal （100） direction. It has also been found that the field caused the increase of primary dendrite arm spacing at the growth speed of R=100 μm/s. Above phenomena are analyzed on the base of theories of the TEMHD and crystal magnetic anisotropy.