The diversity of evolution behavior between stoichiometric and non-stoichiometric AlTM intermetallics in Mg melt

In this study, Al-5Ti, Al-18Si-5Ti, Al-12Si-2Sc and Al-12Si-1Sc-1Zr alloys, containing the Al₃Ti, Ti₇Al₅Si₁₂, AlSi₂Sc₂ and AlSi₂(Sc, Zr)₂ particles, respectively, were introduced into a Mg melt to understand the morphological and structural evolution behaviors of AlTM intermetallic compounds. Deposition layers at the bottom of the Mg melt were obtained due to the particle settlement. Scanning electron microscope and X-ray diffraction were employed to analyze the phase morphologies and structures of the AlTM intermetallic compounds in the deposition layers. A morphological transformation, characterized by the cracking of particles into fine clusters, was observed in all these AlTM intermetallic compounds, which is promoted by the inward diffusion of Mg atoms. The phase structures of the final particles remained Al₃Ti and AlSi₂Sc₂ when Al-5Ti and Al-12Si-2Sc alloys were introduced into the Mg melt, indicating no structural evolution. However, structural evolutions were detected from Ti₇Al₅Si₁₂ to Ti₅Si₄ and from AlSi₂(Sc, Zr)₂ to SiScZr when they were introduced in the Mg melt. It is hypothesized that the crystal structure, whether stoichiometric or non-stoichiometric, is closely related to the structural evolution behavior of AlTM intermetallic compounds. This work may provide new insights into phase control by introducing one type of metal matrix master alloy into another metal melt.