Effect of processing temperature on the microstructure of Al-7Ti master alloy and on refinement of α-Al dendrites in Al-7Si alloys

The present work aims at evaluating the grain refining performance of Al-7Ti master alloys with different microstructures on Al-7Si alloys. Al-7Ti master alloys were prepared in an induction furnace by salt route involving the reactions between K2TiF6 and molten Al. Reaction temperatures chosen for producing Al-7Ti master alloys were 800 o C, 900 o C and 1000 o C while reaction time was kept constant at 60min. These indigenously prepared master alloys at different temperatures were characterized by chemical analysis; particles size analysis, XRD and SEM/EDX microanalysis. Results of particle size analysis suggest that mean size of Al3Ti intermetallic particles in Al-7Ti master alloys were increased from 15.8µm to 22.4 µm as temperature is increased from 800 o C-1000 o C. SEM/EDX studies revealed fine blocky morphology, large blocky and flaky/petal morphologies of Al3Ti intermetallic particles in Al-7Ti master alloys at 800 o C, 900 o C and 1000 o C respectively. Results of grain refinement studies suggest that Al-7Ti master alloy prepared at reaction temperature of 800 o C shows better grain refinement performance on Al-7Si alloy when compared to the Al-7Ti prepared at 900 o C and 1000 o C. In future, the influence of reaction time on microstructural and grain refining behaviour of Al-7Ti master alloys will be evaluated and the performance of these Al-7Ti master alloys will be compared with Al-B and Al-Ti-B master alloys.