Microstructure evolution of as-cast Mg-5Sn alloy with Ba addition

This work lays great emphasis on the effect of Ba addition on microstructure evolution of magnesium alloy Mg-5Sn. It is found that the Mg2Sn phase in Mg-5Sn alloy adopts nearly spherical or plate-like morphology, the morphology distinct from the previously reported irregularshape. One thing to be noted is that most of those spherical particles have a distinct defect contrast in the interior. Our results reveal that with trace addition of Ba, a new BaMg2Sn2 phase forms distributed along the grain boundaries, and both the Mg2Sn phase and the secondary dendrite arm spacing of primary alpha-Mg phase are refined. Even more surprising is that the feather-shaped or needle-like BaMg2Sn2 phase is composed of numerous nanocrystals with a radius less than 50 nm rather than a monocrystal, in contrast to a large extent with Mg2Sn phase, a phase to be only a monocrystal. This unusual phenomenon seems to be greatly tied to the oriented attachment mediated growth mechanism of BaMg2Sn2 phase. (C)15 Elsevier B.V. All rights reserved.