Abstract: The reactions between Ti and Al-Mg alloys were systematically investigated by heating the Ti/Al-Mg alloy powder mixture compacts with Mg contents ranging from 5.09 to 40.36 wt.% at 660 °C. Mg element in the Al-Mg alloys contributed to the breakage of the oxide films on the surfaces of the Ti and Al-Mg alloy powders, thus, promoting the reactions. In the samples with Mg contents varying from 5.09 wt.% to 25.93 wt.%, the first-formed intermetallic compound was Al₁₈Ti₂Mg₃, and then Al₃Ti generated at the Al₁₈Ti₂Mg₃/Ti interface. Since the Mg content in the Al-Mg melts decreased during the subsequent heating process, the previously formed Al₁₈Ti₂Mg₃ in the Ti/Al-5.09Mg sample transformed into Al₃Ti accompanied by the reaction of Al with Ti to newly form Al₃Ti, generating a single Al₃Ti phase. In contrast, the new formation of Al₃Ti and its transformation to Al₁₈Ti₂Mg₃ proceeded continuously in the Ti/Al-13.54Mg and Ti/Al-25.94Mg samples, resulting in a mixture of Al₁₈Ti₂Mg₃ and a little Al₃Ti residue. In the Ti/Al-40.54Mg sample, Al₃Ti was the unique reaction product throughout the heating process. The final Al₃Ti particles in the Ti/Al-5.09Mg sample were in a blocky shape, while they were in a plate-like form in the Ti/Al-40.54Mg sample, which was caused by the enhanced growth anisotropy due to the decreased interfacial energy between Al₃Ti particles and Al-Mg melts with the increase of Mg content. A twin plane re-entrant mechanism was suggested for the growth of Al₁₈Ti₂Mg₃ particles, weakening the anisotropic growth caused by the directional supply of Ti atoms, and contributing to the blocky morphology of Al₁₈Ti₂Mg₃ particles. In addition, the volume difference between the formed Al₁₈Ti₂Mg₃ and consumed Ti was greater than that between the Al₃Ti and Ti, and the Al₁₈Ti₂Mg₃ has worse plasticity than the Al₃Ti, resulting in the Al₁₈Ti₂Mg₃ reaction product fracturing more easily during thickening, thus forming a petal-like structure, but the Al₃Ti product being in an almost continuous layer.

Key words: Mg content, Intermetallic compound, Phase transformation, Morphology, Twin