TITANIUM CARBON ALUMINIUM : A NOVEL GRAIN REFINER FOR ALUMINIUM-LITHIUM ALLOYS

This work explores the possibility of achieving grain size control in aluminium-lithium alloys with the titanium carbon aluminium (TiCAl) master alloys invented at the Technical University of Berlin and developed by London and Scandinavian Metallurgical Co Ltd (LSM). Grain refining tests were conducted on a single batch of 8090 alloy using addition rates of 0.2wt% and 0.4wt% of TiCAl and 3/1 titanium boron aluminium (TiBAl). Other tests using 0.4wt% of binary TiAl gave poor results, showing that the grain refinement obtained from TiCAl was not due to the titanium content alone. Results with the ternary master alloys show a decrease in grain size with increase in grain refiner addition. At the lower addition rate TiCAl gives a smaller grain size in the alloy than does TiBAl, but at the higher rate the difference in grain size is less marked. Test-to-test variation is less severe with TiCAl ; at 0.4wt% addition rate TiCAl gives controlled grain refining in 8090 alloy to a grain size of about 200 microns