铝合金熔体偏析提纯过程中锰元素分配系数调控机理研究

It is difficult to effectively remove the impurity elements whose partition coefficients are close to 1, Such as Mn, when segregation method is used to purify secondary aerospace aluminum. It severely restricts the application of segregation purification method in the high quality secondary aluminum industry. In this proposal, to remove the excess Mn from the recycled aerospace aluminum alloy, a novel approach has been proposed by the applicants to decrease the partition coefficient of Mn in Al alloy melt by using the strong interaction between Mn and Si, with the purpose to improve the purification efficiency of Mn. By coupling the CALPHAD method with micro scale solidification model, the influence of the initial Mn concentration, the atomic ratio of Si to Mn as well as the solidification rate on the partition coefficients of solute in Al-Mn-Si system are investigated, and the corresponding relationship among the composition, solidification rate, solid fraction and the partition coefficients of solute can be established. Furthermore, the ab initio molecular dynamics calculation is used to study the structural characteristics of Al-Mn-Si melt and the migration path of solutes nearby the solidification interface. Combining the spatial distribution of the solutes which can be obtained by the quenching during the segregation purification experiments, the mechanism for the formation of preferred clusters and the migration behavior of solutes nearby the solid-liquid interface in Al-Mn-Si melt can be revealed, which is the theoretical basis for the establishment of the regulatory mechanism of the partition coefficient of elements. This work has a positive significance to develop an efficient purification technology for the metal and semiconductor material.

偏析法提纯再生航空铝合金时无法有效去除Mn等溶质分配系数接近于1的杂质元素，严重制约了偏析提纯方法在高品质再生铝领域的应用。本项目提出通过Mn、Si元素间强交互作用降低铝熔体中难偏析Mn元素溶质分配系数，提高再生铝熔体中Mn元素偏析净化效率的新思路。利用相图计算耦合微观凝固模型，研究Al-Mn-Si熔体中Mn初始浓度、Si/Mn原子比和冷却速率等关键因素对溶质分配系数的影响规律，建立熔体成分、冷却速率和固相分数与溶质分配系数的对应关系。并通过分子动力学方法计算Al-Mn-Si熔体中熔体结构特征和凝固界面处溶质元素迁移路径，结合偏析提纯时对熔体快速冷淬获得的溶质原子空间位置分布特征，揭示元素交互作用下Al-Mn-Si熔体中溶质元素择优成簇机理和凝固界面处溶质原子迁移行为，为元素交互作用下溶质元素分配系数调控奠定理论基础。上述研究工作对于建立高效的金属及半导体材料偏析提纯技术具有积极意义。

偏析法提纯再生航空铝合金时无法有效去除铝熔体中Mn等平衡分配系数接近于1的杂质元素，严重制约了偏析提纯方法在高品质再生铝领域的应用。本项目较为系统地研究了Si元素对铝熔体中Mn元素偏析行为的影响。利用相图计算方法耦合微观凝固模型，研究了Si/Mn原子比、冷却速率对Al-Mn-Si熔体中溶质元素分配系数的影响规律，发现随着凝固速率增加，Mn的溶质分配系数有明显的下降，但凝固初期Mn元素溶质分配系数的变化较慢，随着固相分数的增加，变化速率会急剧增加。尤其Si/Mn较高时，可能是由于合金成分与凝固速率的影响叠加的原因，Mn的溶质分配系数降低更为明显。基于从头算分子动力学计算方法研究了Al-Mn-Si三元合金熔体的团簇特性，结果表明Mn和Si之间可能存在较强的相互作用，从而导致Mn-Si偏好成键，但Mn和Si并不是一直成键，而是存在一定的结构起伏，即成键和非成键交替出现。此外，偏析提纯实验也表明Si的引入一定程度上促进了Mn元素向液相排出。本研究工作探索了铝熔体偏析提纯时Mn元素溶质分配系数的调控方法，对于铝合金废料高效偏析净化技术的建立具有积极意义。