强磁场作用下二元铝合金凝固行为之晶体学研究

The aim of the present research project is to explore the effect of high magnetic field on the solidification behaviors of binary aluminium alloys from the perspective of crystallography and to investiate the macro- and microstructures under different high magnetic fields, such as the growth, distribution, arrangement, aggregation, size and nucleation number of the primary phases and the morphology of the corresponding matrixes. Considering the intimate relationship between the final morphology of the solidified structure and its related crystallographic features, EBSD technology will be made full use of to accurately acquire the orientation data of the crystallized microstructures of the experiment samples, and then the crystallographic features of the primary phases and matrixes (e.g. preferential growth direction, growth interface (facet) indices, orientation, misorientation, certain crystallographic direction (parallel or perpendicular to the magnetic field) and twinning of the primary phase; respective orientations of the two phases in the eutectic matrix; orientation relationship between the two phases in the eutectic matrix; orientation relationship between the primary phase and one of the two phases in the eutectic matrix, etc.) will be caculated and determined with the related crystallographic theory and softwares. Based on the solidification theory of alloys under high magnetic field, plus the analysis of the relationship between the crystallographic features of the primary phases & matrixes and the magnetic field, the mechanism of the macro- and microstructural modification induced by the magnetic field will be deeply discussed.

本科研项目旨在从晶体学角度探讨强磁场对二元铝合金凝固行为的影响，考察在不同强磁场条件下合金凝固的宏微观组织差异，如初生相的长大、分布、排列、聚合、尺寸、形核数目等及相应基体形貌。考虑到合金凝固组织的最终形貌与它们的晶体学特征密切相关，本项目将充分利用EBSD技术，精确采集实验后样品结晶组织微区的取向数据，结合相关晶体学知识和软件实现初生相和基体晶体学特征（初生相的择优生长方向、生长界面指数、取向、取向差、平行或垂直于磁场方向的特定晶体学方向和孪晶；共晶体中两相的分别取向；共晶体中两相之间的取向关系；初生相与共晶体中某一相之间的取向关系等）的计算和确定。基于强磁场下合金凝固理论，结合分析不同的磁场条件与初生相和基体晶体学特征的关系，最终深入探讨磁场导致样品所呈现的宏微观组织形貌的改变机理。

目前，强磁场作用下的合金凝固实验对象种类较少，因此有必要进一步扩大研究对象的范围。其次，在考察凝固组织形貌时，较少全面描述其晶体学特征，从而不能深入的掌握组织变化信息。基于此，本项目在强磁场下凝固了Al-95.55wt.%Zn，Al-3.25wt.%Mn和Al-3Ti-1B合金及固态Cu/液态Al，液态Pb/液态Sn和液态Sn/液态Zn扩散偶，研究了磁场对初生富锌β，Al6Mn和Al3Ti相的析出行为及α-Al,β-Sn和β-Zn的定向生长行为的影响。利用EBSD技术对各初生相和相关组织进行了晶体学表征，分析了磁场对初生相及相关组织的影响机制。对于Al-95.55wt.%Zn合金，初生β枝晶由沿<0001>方向生长较慢的主干轴和从上面长出的沿<10-10>方向快速生长的六个二次枝晶臂构成的扁平晶体。施加的磁场趋于消除初生β枝晶的重力偏析，并使初生β枝晶发生旋转：<0001>方向趋于垂直于磁场方向取向。对于Al-3.25wt.%Mn合金，初生Al6Mn相呈四棱柱形貌。施加的磁场诱发初生Al6Mn相在锐棱处分叉，形成“聚合物”，并趋于消除其重力偏析。此外，磁场还使初生Al6Mn相发生旋转：<100>方向趋于平行于磁场方向取向。对于Al-3Ti-1B合金，初生Al3Ti相呈四棱柱形貌。施加的磁场使样品底部形成的沉积层厚度和α-A晶粒尺寸增加，并趋于使样品上部与沉积层交界处长棒状和沉积层中细小的性初生Al3Ti相发生旋转：<100>方向趋于平行于磁场方向排列。对于固态Cu/液态Al扩散偶，α-Al枝晶自上而下呈现定向生长特点。施加的磁场使得α-Al呈现出规则排列生长和一致偏转。对于液态Pb/液态Sn扩散偶，施加的1-5T磁场使β-Sn枝晶呈现较为规则的定向生长形貌，但相对于纵轴方向发生了一定程度的偏转。对于液态Sn/液态Zn扩散偶，β-Zn枝晶呈片状生长，随磁场强度的增加，趋于规则排列，并以c轴垂直于磁场的方向取向。本项目在实验和理论上丰富了EPM领域的知识。