age and corresponding EDX analysis in Figure 15 show the presence of Ti bearing oxide particles within the AZ91E microstructure. During solidification the Ti particles would move towards the grain boundaries and restrict grain growth because of the near zero solubility of Ti in Mg at a melt tem- perature of 720C. The oxide most probably formed during TEM sample preparation. The presence of carbon is possibly a result of contamination from the graphite mold walls.


Discussion


that provided nucleating sites and restricted grain growth as observed by Liu et al.12


and Wang et al.21


After five minutes of holding, the introduction of the Al- 5Ti-1B grain refiner into AZ91E Mg alloy had a minimum grain size of 323 µm at an addition level of 0.1 wt.%. The Al-5Ti-1B grain refiner contained mostly fine TiB2


particles respectively. Fur-


ther, microscopy analysis is required to determine the more effective nucleating particle, AlB2


Al-1Ti-3B grain refiner to AZ91E led to a minimum grain size of 361 µm at an addition level of 1.0 wt.% after five minutes of holding. An increased amount (1.0 wt.% as compared to 0.1 wt.%) of Al-1Ti-3B grain refiner was required to obtain comparable grain sizes to that of Al-5Ti-1B because of the fewer refining particles observed within the Al-1Ti-3B grain refiner and clustering of TiB2


with Mn-Al particles.


Using simple stoichiometry, it was possible to determine of the amount of nucleating particles available within each grain refiner. For the Al-5Ti-1B grain refiner, one weight percent of


the increase in grain size with increasing addition level. The authors suggest that the Al-5Ti-1B grain refiner shows poor grain refining efficiency at 0.5 and 1.0 wt.% addition levels because of TiB2


or TiB2 particle agglomeration. The introduction of


and the reason to


(b) (a)


Figure 14. SEM image of grain boundary region of AZ91E + 5 wt.% Al-1Ti-3B (a) TiB2 particles at grain boundary and (b) EDX analysis of TiB2


particles.


(a)


(b)


Figure 15. TEM image of AZ91E + 1.0 wt.% Al-1Ti-3B after five minutes of holding (a) Ti bearing oxide within and around grain boundaries and (b) EDX analysis of Ti bearing oxide particle.


38 International Journal of Metalcasting/Spring 11


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