Formation of intermetallic compounds during reaction between Ti and Al–Mg alloys with various Mg contents

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.