Effect of ultrasonic melt processing and Al-Ti-B on the microstructural refinement of recycled Al alloys

Refining the α-Al grain size and controlling the morphology of intermetallic phases during solidification of Al alloys using ultrasonic melt processing (USMP) and Al-Ti-B have been extensively used in academic and industry. While, their synergy effect on the formation of these phases has not yet clearly demonstrated. In this paper, the influence of USMP and Al-Ti-B on the solidified microstructure of multicomponent Al-4.5Cu-0.5Mn-0.5Mg-0.2Si-xFe alloys (x = 0.7, and 1.2 wt%) has been comparatively studied. The results show that the USMP + Al-Ti-B method produce a more profound refinement effect than the individual methods. In addition, the area of single Fe-rich phases in both alloys with USMP + Al-Ti-B are also refined compared with conventional methods. A mechanism is proposed for the refinement, which are the deagglomerated TiB2 parties induced by USMP providing more effective nucleation sites for α-Al, and the refined interdendritic regions limited the growth of Fe-rich phases in the following eutectic reaction. Finally, the application of combined USMP + Al-Ti-B methods is feasible in microstructural refinement, resulting in the improving the casting soundness and mechanical properties of alloys.