Microstructure and its influence on refining performance of AlTiC master alloys

Abstract

The microstructures of four different AlTiC master alloys produced through a new method involving the reaction of pure Ti and carbon in an Al melt have been examined using XRD, SEM, EPMA, and TEM, and their re ning ef ciencies tested. Individual TiC particles were found to be single crystals with polyhedral or spherical morphologies. In addition to the aluminium matrix, Al -5Ti -0 . 3C (wt-%) re ners contain TiC and TiAl 3 phases, whereas Al -8 . 4Ti -1 . 8C contains only TiC. Three types of agglomerating behaviour of TiC particles, namely discrete particles, homogeneously distributed clusters, and compact blocks along grain boundaries, were found in master alloys produced at different temperatures, and these further in uence the re ning performances. Ti was found to play an important role in the re nement of Al by AlTiC re ners; observation of grain centres showed that TiC particles are located at the grain centre and the excess Ti segregates to them and forms a roselike structure around them. It is clear that the re nement of Al by AlTiC results from the combined action of TiC and Ti, and it is possible that AlTiC and AlTiB share some common rules in re ning Al. Possible re nement mechanisms have been discussed based on microstructure observations and previous studies. MST/5542The authors are in the Key

Preparation of Al-Ti-B-C Master Alloy and its Grain Refinement Effect for Pure Al

“…7). We have concluded that Al-Ti-C and Al-Ti-B master alloys share some common rules in refining Al [7], which can be further confirmed in the present work. In the Al melt with the addition of Al-Ti-B or Al-Ti-C mastera alloys, surplus Ti atoms as solute have been observed to segregate to TiB 2 or TiC particles [11][12][13]7].…”

“…We have concluded that Al-Ti-C and Al-Ti-B master alloys share some common rules in refining Al [7], which can be further confirmed in the present work. In the Al melt with the addition of Al-Ti-B or Al-Ti-C mastera alloys, surplus Ti atoms as solute have been observed to segregate to TiB 2 or TiC particles [11][12][13]7]. It is possible that an especially thin layer of TiAl 3 phase forms at surfaces of TiB 2 or TiC particles due to the segregation of Ti, then this phase acts as substrates for the nucleation of α-Al [12][13].…”

“…This difference between the two master alloys is most probably because there is surplus Ti (mainly combined in TiAl 3 ) in addition to that combined in TiB 2 and TiC particles in Al-5Ti-0.82C-0.23C. In the study of Al-Ti-C master alloy grain refiner, the similar phenomenon that Al-Ti-C master alloy containing both surplus Ti and TiC particles exhibites a higher refinement efficiency than the one with only TiC particles, has been constantly observed, and it was attributed to the fact that the refinement ability of Al-Ti-C results from a combined action of TiC particles and surplus Ti [7,10]. In the case of Al-Ti-B master alloy, the surplus Ti in addition to TiB 2 particle was also argued to play an important role in the nucleation of Al grain (see citations in Ref.…”

“…The refinement effect of Al-Ti-B-C master alloys for commercial pure Al (99.7wt.%) was tested by a KBI ring method described detailedly in Ref. 7.…”

Al-Ti-C grain refiner made by ultrasonic levitation

“…Comparing to Al-Ti-B grain refi ner, the TiC, a heterogeneous nucleation core, has less conglomeration tendency than TiB 2 and is immunizing to Zr, Cr, Mn, and V [2] . Al-Ti-C is studied emphatically and is a novel kind of grain refi ner with better application prospect [3][4][5][6][7][8][9] .…”