Evolution of secondary phase particles during deformation of Al-5Ti-1B master alloy and their effect on α-Al grain refinement

Abstract Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl 3 and TiB 2 in Al-5Ti-1B alloy are the main secondary-phase particles for refinement, while the understanding on the effect of their sizes on α-Al grain refinement continues to be fragmented. Therefore, Al-5Ti-1B alloys with various sizes and morphologies of the secondary-phase particles were prepared by equal channel angular pressing (ECAP). Evolution of the secondary-phase particles during ECAP process and their impact on α-Al grain refinement were studied by X-ray diffraction and scanning electron microscope (SEM). Results show that during the ECAP process, micro-cracks firstly appeared inside TiAl 3 particles and then gradually expanded, which resulted in continuous refinement of TiAl 3 particles. In addition, micro-distribution uniformity of TiB 2 particles was improved due to the impingement of TiAl 3 particles to TiB 2 clusters during deformation. Excessively large sizes of TiAl 3 particles would reduce the number of effective heterogeneous nucleus and thus resulted in poor grain refinement effectiveness. Moreover, excessively small TiAl 3 particles would reduce inhibitory factors for grain growth Q and weaken grain refinement effectiveness. Therefore, an optimal size range of 18–22 μm for TiAl 3 particles was suggested.