Microstructure and grain refining performance of melt-spun Al-5Ti-1B master alloy

In the present work, the microstructure and grain refining performance of the melt-spun Al-5Ti-1B (wt%) master alloy have been investigated, using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and grain refining tests. It has been found that the microstructure of the melt-spun At5Ti- 1B master alloy is mainly composed of two phases: metastable, supersaturated a-Al solid solution and uniformly dispersed TiB2 (particles, quite different from that of the rod-like alloy consisting of three phases: a-Al, blocky TiAl)(, and clusters of TiB)(3)(2) particles. Quenching temperatures and wheel speeds (cooling rates), however, have no obvious effect on the microstructure of the melt-spun Al-5Ti-1B alloy. Grain refining tests show that rapid solidification has a significant effect on the grain refining performance of Al-5Ti-1B alloy and leads to the great increase of nucleation rate of the alloy. Nevertheless, the melt-spun Al-5Ti-1B master alloy prepared at different wheel speeds and quenching temperatures possesses the similar grain refining performance. The reasons for the microstructure formation and the improvement of the grain refining performance of the melt-spun Al-5Ti-1B master alloy have been also discussed. 2002 Elsevier Science B.V. All rights reserved.