Influence of C/Ti stoichiometry in TiCx on the grain refinement efficiency of Al-Ti-C master alloy

doi:10.1016/j.jmst.2017.04.015

Abstract

Abstract:

TiC_x contained Al-Ti-C is a kind of grain refiner for Al alloys. In this work, the influence of C/Ti stoichiometry, i.e. the x value in TiC_x on grain refinement efficiency was investigated. TiC_x particles have been obtained in five Al-5Ti-mC (m = 0.1, 0.5, 0.8, 1, 1.25) master alloys and the x values were measured to be 0.72, 0.75, 0.79, 0.81and 0.8, respectively. It was found that the refinement performance of the master alloys had a close relationship with the x value of TiC_x. The Al-5Ti-mC alloy with lower-x TiC_x shows better refinement efficiency and anti-fading capability. It is supposed that TiC_x particles with lower x are more preferred to release Ti atoms during nucleating process and have a better Ti-absorbing capability. This contributes to the Ti-rich zone formation at TiC_x/melt interface, thus enhancing the refinement and anti-fading capability.

Key words: Al alloys, Nucleation, Grain refinement, TiC_x

Yang Huabing, Gao Tong, Wang Haichao, Nie Jinfeng, Liu Xiangfa. Influence of C/Ti stoichiometry in TiC_x on the grain refinement efficiency of Al-Ti-C master alloy[J]. J. Mater. Sci. Technol., 2017, 33(7): 616-622.

Figures/Tables 11

Fig. 1. (a) XRD patterns of Al-5Ti-mC (m = 0.1, 0.5, 0.8, 1 and 1.25 wt%) master alloys; (b, c) microstructures of Al-5Ti-0.5C and Al-5Ti-1.25C, respectively; (d, e) EDS analyses of spectrum 1 and 2 in (b).

Fig. 2. (a) Typical morphology of synthesized TiCx; (b) lattice structure of TiCx crystal (face-centered cubic); (c) XRD patterns of extracted TiCx particles from Al-5Ti-mC; (d) lattice parameter and x value in TiCx as a function of m value in Al-5Ti-mC master alloys.

Table 1 Type and addition level of refiners of six group of grain refinement tests.

Tests	Addition level of refiners	The equivalent amount
		TiC_x	Free Ti
No. 1	0	0	0
No. 2	0.30% Al-5Ti-0.1C	0.002%	0.013%
No. 3	0.063% Al-5Ti-0.5C + 0.23% Al-5Ti	0.002%	0.013%
No. 4	0.041% Al-5Ti-0.8C + 0.25% Al-5Ti	0.002%	0.013%
No. 5	0.034% Al-5Ti-1C + 0.26% Al-5Ti	0.002%	0.013%
No. 6	0.033% Al-5Ti-1.25C + 0.26% Al-5Ti	0.002%	0.013%

Fig. 3. α-Al grain macrostructures of commercial pure Al before and after refined by different master alloys at 720 °C holding for 5 min before solidification in KBI mould: (a) unrefined; (b-f) with simultaneous addition of a certain amount of Al-5Ti-mC, m = 0.1, 0.5, 0.8, 1 and 1.25 wt%, respectively and Al-5Ti to ensure the addition level of TiCx and free Ti are the same.

Table 2 Average α-Al grain size of six groups of refinement tests (Table 1) after the addition of refiners for 5 min (d5) and 60 min (d60), respectively.

Holding time	No. 1	No. 2	No. 3	No. 4	No. 5	No. 6
5 min (d₅)	4200	235	266	328	841	671
60 min (d₆₀)	4180	343	428	574	1598	1241

Fig. 4. Grain refinement fading ratio in 60 min (f60) as a function of m value in Al-5Ti-mC master alloys.

Fig. 5. Lattice parameter of TiCx in Al-5Ti-0.1C as a function of holding time at 720 °C.

Fig. 6. (a) Microstructure and (b) XRD pattern of Al-5Ti-1.5C master alloy.

Fig. 7. Linear scanning analysis for high purity Al (99.99%) refined by 5% Al-5Ti-1.5C: (a) secondary electron image of microstructure; (b-d) results of Al, C, Ti elements, respectively.

Fig. 8. Equilibrium Ti level at the TiCx/Al melt interface as a function of x value in TiCx at 720 °C.

Table 3 Lattice disregistry between α-Al and TiCx in Al-5Ti-mC, m = 0.1, 0.5, 0.8, 1, 1.25, respectively (used in Table 1).

TiC_x	No. 2	No. 3	No. 4	No. 5	No. 6
δ (%)	6.31	6.34	6.38	6.39	6.38

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