A MODEL OF GRAIN REFINEMENT MECHANISM FOR ADDING AL-TI-B MASTER ALLOYS INTO ALUMINUM

摘要

Al-Ti-B master alloys have been used as grain refiner for Al castings for long time, although the mechanism, especially the role of boron in grain refining process, is not very clear till now. In this work, a model based on the study of some Al-5%Ti-1%B master alloys of different microstructures is suggested. According to this model, the Al_(1-x)Ti_xB2 phase in Al-Ti-B master alloys is an additional nucleus for soid Al besides the Al_3Ti phase. The Ti released from Al_(1-x)Ti_xB_2 particles may help the nucleation of α-Al. Due to the surface energy between Al and Al_(1-x)Ti_xB_2, as well as the liquid agitation in Al melt, α-Al nucleates more easily in the grooves between the Al_(1-x)Ti_xB_2 particles of boride clusters than on the individual Al_(1-x)Ti_xB_2 particles.