Al-Ti-B晶粒细化剂研究进展:细化机理及第二相控制

Research Progress of Al-Ti-B Grain Refiner:Mechanism Analysis andSecond Phases Controlling

随着铝合金使用日益广泛,人们对高品质Al-Ti-B晶粒细化剂的需求也日益增加。氟盐法是国内外Al-Ti-B晶粒细化剂制备的主流方法,国内研究者们在氟盐法制备工艺方面取得了一定的成果,但依然未能在高品质Al-Ti-B晶粒细化剂的制备上获得突破。Al-Ti-B晶粒细化剂的细化机理主要有硼化物粒子理论、包晶反应理论、双重形核理论等,其中,双重形核理论可以较好地解释Al-Ti-B晶粒细化剂的晶粒细化过程。双重形核理论表明:Al-Ti-B晶粒细化剂中的第二相TiAl 3和TiB 2尺寸越小、数量越多、分布越弥散,则Al-Ti-B晶粒细化剂的细化性能越突出。氟盐反应热力学分析表明:在氟盐反应产物控制方面,TiB 2的生成趋势最大,TiAl 3次之,AlB 2最小;在750~800℃的反应温度范围内,适当缩短反应时间,可在保证TiAl 3生成的同时避免AlB 2的生成。氟盐反应动力学分析表明:TiAl 3和TiB 2的形成由氟盐分解、第二相形核及长大三个过程组成,通过减小氟盐尺寸、提高氟盐分解气体TiF 4和BF 3与Al熔体的接触界面面积、减小Ti、B元素的绝对过饱和度、缩短反应时间等措施,有望获得内含细小弥散第二相的Al-Ti-B晶粒细化剂。本文主要介绍了Al-Ti-B晶粒细化剂的发展历程及制备方法,阐述了国产Al-Ti-B晶粒细化剂与进口产品的差距和存在的问题。基于Al-Ti-B晶粒细化剂的晶粒细化机理、氟盐反应热力学与动力学,讨论了TiAl 3、TiB 2的细化、弥散化控制原理,并对其细化、弥散化控制技术及潜在技术进行了综述和展望。

With the widespread usage of aluminum alloys,the demand for high-quality Al-Ti-B grain refiner is increasing.Fluoride salt method is the mainstream preparation method of Al-Ti-B grain refiners at home and abroad.Domestic researchers have made many efforts to improve the fluoride salt reaction preparation technology of Al-Ti-B grain refiner and obtained some research achievements.However,a breakthrough in preparing the high quality Al-Ti-B grain refiner has not been achieved.The main refining theories of Al-Ti-B grain refiner are the boron particle theory,the peritectic reaction theory and the duplex nucleation theory and so on.Among them,the duplex nucleation theory can explain the grain refining process of Al-Ti-B grain refiner well.The duplex nucleation theory indicates that if the size of the second phase TiAl 3 and TiB 2 is smaller,the number of the second phase TiAl 3 and TiB 2 is higher,the second phase TiAl 3 and TiB 2 is more evenly distributed,the refining performance of Al-Ti-B grain refiner is better.The thermodynamics analysis of fluoride salt reaction shows that the generation trend of TiB 2 is the largest,followed by TiAl 3 and AlB 2 is the smallest.During 750—800℃,shortening the reaction time properly can guarantee the forming of the TiAl 3 and avoid the forming of the AlB 2 at the same time.The dynamics analysis of fluoride salt reaction shows that the forming of the TiAl 3 and TiB 2 composed of three steps,the decomposition of fluoride salt,the nucleation of the second phase,and the growth of the second phase.By decreasing the size of the fluoride salt,increa-sing the contact area between the decomposition gases(TiF 4 and BF 3)and the aluminum melt,decreasing the absolute saturation of titanium and boron,and shortening the reaction time can gain tiny and dispersive second phase.This paper mainly introduces the development history and the mainstream preparation methods of Al-Ti-B grain refiner,describes the gap and the existing problems between domestic and imported Al-Ti-B grain refiners.Based on the grain refinement mechanism of Al-Ti-B grain refiner,the thermodynamics and kinetics of fluoride reaction process,the control principle of refinement and dispersion of TiAl 3 and TiB 2 is discussed,the relevant control technology and potential technology are reviewed and prospected respectively.