Aluminum / Aluminium Titanium Carbon (AlTiC) - TiCar®

When comparing grain refiners, test data supports that more Al-Ti-C than Al-Ti-B grain refiner is required to achieve an equivalent grain size, though Al-Ti-C is reported to be more effective in alloys containing zirconium and chromium in the presence of magnesium. In addition, the use of Al-Ti-C grain refiner can provide opportunities in other alloys for cost savings by improved ingot quality and increased production rates. Some of these considerations are highlighted below.

1. Higher casting speeds have been reported using Al-Ti-C than Al-Ti-B grain refiners in certain alloys. Higher yields due to fewer oxide patches, less cracking, bleed-out, and smaller center-line grain size have also been reported.

2. AA5182 is prone to oxide patches that can lead to bleed-out if Al-Ti-B grain refiner is overused. Oxide patches are usually ascribed to the small amount of fluoride salt associated with Al-Ti-B grain refiners. This is not a problem with the use of TICAR® grain refiners since TICAR® is produced by a process that does not use salt. Patches have even been observed when casting under an inert atmosphere.

3. There is evidence that TiC does not wet, and therefore, does not decorate oxide films as does TiB2. Therefore, the use of Al-Ti-C may extend filter life by reducing the capture of desirable particles.

4. Similarly, because fewer TiC particles are captured in a filter, better utilization of the grain refiner occurs and the potential for particle showers is reduced. Capture rates by filters of 10% to 50% of TiB2 particles have been reported. The actual capture rate can vary depending on metal cleanliness, filter rating, etc.

5. Because TiC particles decorate oxides less than TiB2 particles, in applications where alloys such as AA5657, 5252, etc., are anodized or bright finished, the potential for "razor streaks" or other surface defects is minimized.

6. Unlike Al-Ti-B, Al-Ti-C grain refiners are relatively sensitive to casting temperature. For Al-Ti-C, lower introduction temperatures (< 732"C) and lower casting temperatures are required to assure optimum grain refining effectiveness.

7. With either TIBOR® or TICAR® alloys, the residence times must be sufficient for the aluminides to dissolve. This is usually about one minute for rod products, but the residence time should not exceed five minutes for the Al-Ti-C alloy due to its higher fade potential.

8. Literature shows, and our work explains, why the spread in grain size from the perimeter to the center of a billet or ingot is less when using Al-Ti-C than the Al-Ti-B refiner. However, if insufficient grain refiner is added, Al-Ti-C is more prone to the twin columnar grain structure (TCG). TCG can lead to "ghost" grains for bright trim alloys and cracking in 2XXX and 7XXX alloys. Even a very coarse grain size will re-crystallize to a fine grain size on hot working, but TCG will persist.

9. In a recent publication, laboratory tests revealed that TiC particles substantially grew (>20 Microns) within a time period of 20-30 minutes under moderate stirring (60RPMS). This study identifies a possible theory for the rapid fade characteristics of Al-Ti-C under certain circumstances, as these larger particles will settle. This suggests that to optimize grain refining while using Al-Ti-C, the residence time should be minimized and unnecessary stirring of the melt should be avoided after the addition of the grain refiner. One should strongly consider adding Al-Ti-C downstream of metal treatment to maximize effectiveness. The data suggests that stirring practices for grain size tests should be examined to assure consistency of response in laboratory evaluations.

10. TiC particles are not as hard as TiB2 due to a lower Mohs hardness. In the case of extrusion and similar alloys, the smaller TiC particle volume for the same grain refining level means less draw and extrusion die wear as well as longer roll life and a better surface finish when machining.

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Al TiCar® Titanium Carbon