大过饱和度下原位TiB2粒子高效细化铝合金机理研究

Grain refinement of aluminium alloys by adding Al-Ti-B master alloys to the melt has become a common industrial practice. A lot of researches were carried out to uncover the grain refinement mechanisms as well as to show the microstructure formation under the effect of grain refiner. These researches demonstrate that an excellent grain refinement can be achieved only with the presence of solute Ti and TiB2 particles of a proper average size and a narrow size distribution. However, the classical grain refinement treatment can’t meet the requirements for manufacturing the high-quality aluminium alloys due to the large size and wide size distribution of TiB2 particles in the Al-Ti-B master alloys. This project proposes a new idea for high-efficiency grain refinement in aluminium alloys by in situ TiB2 particles formed under high supersaturation. The TiB2 particles with a narrow size distribution and proper average size in the melt are prepared through the reaction of Al-Ti with Al-B melt. The resultant Al-Ti-B melt are directly employed to refine the aluminium alloys. This project will explore the controlling principle for the size distribution of TiB2 particles as well as the key influence factor for the grain refinement results. The implementation of this project will provide a new design idea for the grain refinement of high-performance aluminium alloys.

工业生产中常用Al-Ti-B中间合金细化铝合金铸态晶粒组织。有关Al-Ti-B对α-Al晶粒细化机制及对铝合金凝固组织影响的研究已很深入，并取得了显著进展。研究表明，铝合金熔体中同时存在溶质Ti和尺寸适当且分布集中的TiB2粒子时，晶粒细化效果较好。然而，采用传统方法制备Al-Ti-B时，很难制备尺寸分布集中的TiB2粒子，晶粒细化效果已不能满足高性能铝合金的生产需求。项目提出通过瞬间充分混合近饱和的Al-Ti、Al-B熔体，使TiB2在大过饱和度下大量形核、长大，形成尺寸分布集中的粒子，并用其直接细化铝合金的思想；澄清TiB2粒子沉淀析出机制和尺寸及其分布的调控方法，探明原位TiB2粒子高效细化铝合金的关键影响因素。本研究将为高品质铝合金凝固组织的细化提供新的设计思想。

向合金熔体中添加Al-Ti-B中间合金是目前工业生产中广泛使用的一种铝合金凝固组织细化方法。研究结果表明铝合金熔体中同时存在溶质Ti和尺寸适当且分布集中的TiB2粒子时，晶粒细化效果较好。然而，传统方法制备的Al-Ti-B中TiB2的尺寸分布较宽，细化效果有限，已不能满足高品质铝合金的生产需求。项目开展了原位TiB2粒子沉淀析出行为的实验研究，考察了溶质浓度、反应温度、时间等因素对TiB2粒子沉淀析出行为的影响，建立了TiB2粒子瞬态形核和扩散长大共同作用的群体动力学模型，并结合实验开展了模拟研究，明确了熔体过饱和度对TiB2粒子沉淀析出行为及其尺寸分布的重要性；实验研究了Ti添加量对Al-Ti-B中间合金细化工业纯Al晶粒效果的影响，模拟分析了Al-Ti-B中间合金细化工业纯铝过程中TiB2粒子的溶解、粗化和快速长大行为及溶质Ti的影响，发现，TiB2粒子的动力学行为对中间合金细化能力的影响不可忽视，溶质Ti能有效抑制熔体中TiB2粒子的溶解、粗化和快速长大行为，影响Al-Ti-B中间合金的细化能力；实验与模拟相结合，研究了原位TiB2粒子对铝合金凝固组织的细化效果，明确了原位TiB2粒子高效细化铝合金的关键影响因素。