Effect of Gd on microstructure and refinement performance of Al-5Ti-B alloy

Al-5Ti-B and Al-5Ti-B-Gd master alloy refiners were fabricated by fluorine salt casting method. The microstructure and phase constitution of the master alloys were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Al-Ti-B alloy refiner consists of Al₃Ti phase and TiB₂ phase. After Gd is introduced into the intermediate alloy, Ti₂Al₂₀Gd phase appears in the alloy, the size of Al₃Ti is significantly reduced, and Ti-Al-Gd phase is found in the edge of Al₃Ti phase. At the same time, some independent Ti-Al-Gd phases appear in local areas, which are Ti₂Al₂₀Gd phase determined by micro-area electron diffraction analysis. Analysis and calculation results of the high-resolution images of the Ti₂Al₂₀Gd/Al structure show that there is no other compound at the junction between the Ti₂Al₂₀Gd phase and Al, and Ti₂Al₂₀Gd phase has a great difference in atomic space with the α-Al, which cannot be directly used as heterogeneous nucleus. But, after being decomposed in the aluminum melt, the Ti₂Al₂₀Gd phase can promote the refinement effect of the refiner. In the Al-Ti-B-Gd master alloy, there are many dispersed Al₃Ti particles with a size of less than 1 µm, which can promote the Al-5Ti-B refining effect.