Al-Ti-C中间合金的相组成及其细化特性

Phases and Refining Performances of Al-Ti-C Master Alloys

用专利方法制备出各种成分的Al Ti C中间合金作为铝及铝合金的晶粒细化剂。对该系列中间合金的组织和物相分析表明 :在制备中间合金过程中 ,C与Ti反应充分 ,生成TiC和TiAl3两种第二相 ,且TiAl3析出量取决于中间合金的Ti含量和Ti/C含量比。用于纯铝的晶粒细化试验表明 :与Al Ti B中间合金相比 ,Al Ti C中间合金的晶粒细化效率更高 ;Al Ti C中间合金只有在组织中TiC与TiAl3保持适当比例时 ,才能对纯铝产生良好的晶粒细化效果 ,不含TiAl3的Al Ti C中间合金的晶粒细化作用很微弱 ;用Al Ti C中间合金细化纯铝晶粒时 ,响应时间短 ,但衰退较快 ,且不能通过熔体搅拌法予以消除。分析和探讨了Al Ti C中间合金的晶粒细化机理 ,认为“碳化物理论”不能充分解释Al Ti C的晶粒细化机理 ,提出“Ti在TiC或TiAl3颗粒表面富集引发包晶反应”的晶粒细化机制。

Al-Ti-C master alloys used as grain refiners of the aluminum and its alloys with various titanium and carbon contents have been prepared through a proprietary way which represents such merits as complete reaction of carbon with titanium, no need of external stirring of melt, short reaction time and low production costs etc. Microstructure and phase analysis indicate that TiC and TiAl 3 are the two secondary phases and that the content of TiAl 3 formed depends upon the Ti content and Ti/C content ratio in the master alloy. The tests of grain refinement on the pure aluminum reveal that the Al-Ti-C master alloys have following refining performances of: higher refining efficiency than that of Al-Ti-B master alloys; TiAl 3 is a must constituent for the master alloys refining the pure aluminum efficiently, and the master alloys must have a proper TiC/TiAl 3 ratio in the microstructure for getting the highest refining efficiency, the master alloys without TiAl 3 only get little refining efficiency for pure aluminum; with a short response time but rapid fading which can not be eliminated by stirring the melt. Finely, it is analyzed and discussed that 'Carbide theory', which is commonly believed to be the mechanism of grains refinement of the pure aluminum by using Al-Ti-C, is found not reasonable enough to elucidate some refining performances, and the mechanism of 'Peritectic reaction induced by the concentration of Ti on the surface of TiC or TiAl 3 particles' has been hypothesized partly on the base of the refining performances.