Morphological Evolution of TiB(2) and TiAl(3) in Al–Ti–B Master Alloy Using Different Ti Adding Routes

Three different Ti addition routes were used to prepare an Al–5Ti–B Master Alloy: the halide salt route, the Ti-sponge route, and the partial Ti-sponge route. In the halide salt route, the raw materials were Al + KBF(4) + K(2)TiF(6); K(2)TiF(6) was completely replaced by pure titanium for the Ti-sponge route versus the halide salt route; in the partial Ti-sponge route, K(2)TiF(6) was partially replaced by pure titanium. Here, 30% Ti-sponge or 60% Ti-sponge route means that 30% or 60% K(2)TiF(6) was replaced by pure titanium, respectively. The above Ti addition routes have a significant influence on the growth pattern and morphological evolution of TiAl(3) and TiB(2), which greatly affect the refining performance of Al–Ti–B Master Alloy. When using the halide salt route, a streamlined “rich Ti, B area” exists in the aluminum melt, which is a complex compound of (Ti(x), Al(1−x)) B(y). The “rich Ti, B area” is essential for the nucleation and growth of TiAl(3) and TiB(2). Blocky TiAl(3) was obtained and its average size was 4.7 μm based on the halide salt route. In the Ti-sponge route, the nucleation of TiAl(3) mainly depends on the mutual diffusion of Al and Ti, and TiAl(x) forms around pure Ti particles, i.e., the so-called Ti–TiAl(x) mechanism. The average size of the blocky TiAl(3) was 9.8 μm based on the Ti–TiAl(x) mechanism. For the partial Ti-sponge route, the “rich Ti, B area” gradually decreases with the increase in Ti powder’s contents, and large TiAl(3) coexists with the small TiAl(3). Compared with the Ti-sponge route, the halide salt route can form smaller TiAl(3). In the Ti-sponge route, there is a small amount of “rich Ti, B area” due to the influence of the Ti–TiAl(x) mechanism, which does not meet the requirements of TiB(2) growth. In the halide salt route, there is sufficient “rich Ti, B area”, which is conducive to the formation of TiB(2). Both the crystal defects and the crowded growth environment caused by the “rich Ti, B area” are fundamental reasons for the fragility and the irregular shape of the TiB(2). The refining effect of the Al–Ti–B Master Alloy prepared by the halide salt route is better than the Ti-sponge route. The refining effect of 30% Ti-sponge route is better than that of Ti-sponge route and worse than that of halide salt route.