Impurities in Al–5Ti–1B grain refiner rod

Abstract

Two different Al–5Ti–1B (wt-%) grain refiner rods (Rod A – a 'poor' refiner and Rod B – a 'standard' refiner) were examined using induced coupled plasma – optical emission spectroscopy (ICP-OES), computed tomography (CT) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) spectroscopy. CT with its digital geometrical processing allowed 3D images of non-destructed sections of the rod to be analysed. Results for Rod A revealed the presence of several types of inclusions up to several mm in size. Qualitative micro-chemical analysis using an SEM with EDX indicated that the inclusions were Ti, K and/or F rich. This would thus imply that the particles observed were, undissolved Ti/Al-Ti compounds namely Al3Ti and/or Al3Ti(Si), and potassium and fluoride spent salts namely KF-AlF3 flux. These findings are indicative of an inefficient, non-optimal manufacturing process. An assessment of the grain refining efficacy of both the rods using the TP1 test showed the standard rod (Rod B) to be more effective in promoting refinement. Furthermore, the grain size observed for Rod A was not as consistent. Thus the quality of the grain refiner rod used in industrial practice is important as the grain size, feedability, cleanliness, uniformity of microstructure and integrity of the as-cast part may all be deleteriously affected.