Al-1Ti-3B Al-1Ti-3B Grain Refiner
(3-10 μm) particles in Figures 10B and 10C, respectively. The Ti and Al bearing particles were confirmed as TiB2
μm) and AlB2 the particles observed by Fjellstedt et al.20 and AlB2 1Ti-3B grain refiner contained only TiB2 until the TiAl3
limiting reagent in Equation 3 was TiAl3 with TiAl3
grain refiner, the B content exceeded the Ti:B ratio of 1:2.5 and the microstructure contained TiB2
Aluminum diboride particles can also act as nucleating sites as observed by Suresh et al.13
was exhausted. Therefore, the Al- and AlB2
and no TiAl3 . The AlB2
.11
An SEM image of the Al-1Ti-3B grain refiner is shown in Figure 10A with corresponding EDX analysis of TiB2
(< 3
respectively by once again comparing with For the Al-1Ti-3B
The reacted particles. As compared to the Al-5Ti-1B
An Al based particle was found within the center of a Mg grain as shown in Figure 12A. Similar to the sample in Figure 8, the sample representing AZ91E + 1.0 wt.% Al-1Ti-3B after 5 minutes of holding in Figure 12 was etched prior to SEM analysis to improve image contrast. The observed particle in
grain refiner, the Al-1Ti-3B grain refiner has significantly fewer clusters of fine particles which is a possible explanation for requiring 1.0 wt.% addition level to achieve similar grain refining effects as 0.1 wt.% Al-5Ti-1B grain refiner.
The microstructure also contained some potassium and fluo- rine based particles which could have been K2
salts that did not have sufficient time to react during holding. Figure 11 depicts the residual salt alongside AlB2
TiF6 AZ91E + Al-1Ti-3B
and KBF4 particles.
(b) (a)
Figure 10. SEM image of Al-1Ti-3B grain refiner showing TiB2 (b)EDX analysis of TiB2
particle and (c) EDX analysis of AlB2
and AlB2 particle.
particles (a) SEM image of Al-1Ti-3B,
(c)
(b) (a)
Figure 11. SEM Image of Al-1Ti-3B grain refiner showing residual salt particles (a) SEM image of residual salt particles and (b) EDX analysis of salt particles.
36 International Journal of Metalcasting/Spring 11
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