CONTROL OF SOLIDIFIED STRUCTURES AND INTERGRANULAR PRECIPITATIONS IN Al-Li BINARY ALLOYS BY HIGH MAGNETIC FIELDS

摘要

The present study is undertaken to investigate the effects of high magnetic fields on the solidified structure and grain boundary of binary Al-Li alloy. Al-3wt.%Li alloys were solidified under both uniform and gradient magnetic field conditions. The secondary dendrite arm spacing (SDAS) and area fraction of grain boundary (AFGB) on the longitudinal section of the alloys were measured using metallographic analysis. Morphology and patterns of the precipitates were also analyzed using optical microscopy, scanning electron microscope (SEM), transmission electron microscopy (TEM) and auger electron spectroscopy (AES). It was found that, when imposing a high uniform magnetic field, the SDAS decreased, while the high gradient magnetic fields were observed to have no more obvious effect than the uniform ones on the SDAS. AES and TEM analysis showed that in all cases, the precipitated phases at grain boundary and in a matrix were δ (AlLi) and δ' (Al<'3>Li) phases, respectively. Furthermore, the AFGB decreased at first and then increased with increase of the magnetic flux density under uniform magnetic field, while it decreased in the case of high gradient magnetic field.