Effects Of A High Magnetic Field On The Behavior Of Precipitate Phases In Al-Mn Alloy

The advancement of the material plays an essential role on the development of the national economy and science, because of the fast improving science and technology. Every demand for the new material or techniques is strict and accurate. In material science, it is time to adopt new craft to improve material performance and to develop new technology.Al-Mn alloy has many excellent physics and chemical properties. It is an important metal in the industry fields. If the Mn element distributes equably in the alloy, the hot process property and cold process property is similar to the Al alloy, but the property is higher than that of pure Al. The casting property of Al-Mn alloy is bad, because the solidification zone of it is very narrow, and the fluid is also low. So it is difficult to obtain the ideal alloy in normal condition.Tremendous magnetization energy can be inputted into materials without any contact when the material is placed in a high magnetic field. As a result, the thermodynamic state of the material is changed. At the same time, there are magnetic forces generated in the material. Therefore, the solidification and other phase transformations, the microstructure, shape and distribution of the crystals in the material may be influenced dramatically by the high magnetic field. It shows prosperous future in application and a new area about application of a high magnetic field in processing materials is opened for research.This thesis summarized some relevant developments and main performances of the high magnetic field applied in the research in the past. The solidification behaviors of the Al₆Mn precipitated phase in Al-Mn alloys under high magnetic fields up to 12T have been experimentally studied. The phenomena, behavior and mechanism during the solidification and the evolution of the precipitated phases structure have been examined intentionally and systematically, along with the theory to explain the experimental results. Moreover, the thermodynamics of solidification of pure metals in a high magnetic field has been studied primarily. Following are the main results:1. The precipitated phases Al₆Mn in Al-Mn alloys are oriented with their c-axes parallel to the applied high magnetic field. And it is also found that the longitudinal axes of the Al₆Mn crystals are perpendicular to their c-axes and the laminated alignment structure perpendicular to the applied field is formed.2. The microstructures of Al-5%Mn alloy after the entire melted state and the half solicited state are similar. But the latter's microstructures are tinier and smaller.3. All of the Al-5%Mn alloy can form the orientated microstructures under the different intensity high magnetic field. And with the increase of the magnetic field intensity and size of the Al₆Mn crystals, the extent of the orientation is also increasing.4. The extent of Al₆Mn crystal's aggregation and growth gradually enhances with the time of heat holding becomes longer and longer.5. According to the theoretical analysis, the ferromagnetic crystals with magnetic anisotropy tend to turn their crystal axes with maximum susceptibility parallel to the direction of the magnetic field, and the diamagnetic crystals with magnetic anisotropy tend to the crystal axes with absolute maximum susceptibility perpendicular to the direction of the applied field.