Effect of TiB2 particulate on partial remelting behavior of Mg-11Al-0.5Zn matrix composite

Partial remelting behaviors of Mg-11Al-0.5Zn alloy and TiB2/Mg-11Al-0.5Zn composite are investigated by the isothermal holding at the temperatures of 510 and 545 degreesC. The result shows that, although, the TiB2 addition has no influence on the remelting characteristics of eutectic and liquidus temperatures of the composite, it has a great effect on the remaining liquid located at the grain boundary. With a processing temperature of 545 degreesC, the remaining liquid is dramatically decreased in the composite, compared with that in the unreinforced matrix alloy. Furthermore. the solid alpha-Ma grain size in the composite does not significantly reduce compared with that in the matrix alloy; however, the microhardness of the alpha-Mg grain is increased in the partial remelting microstructure in the composite. Although most of the TiB2 particulates are present in the remaining liquid phases distributed at the grain boundaries, some liquid islands are entrapped inside alpha-Mg grains. As a consequence, the TiB2 particulates can eventually reside within the grains after complete solidification. However, it is difficult that TiB2 particulate is directly incorporated (engulfed) into the Mg-11Al-0.5Zn matrix alloy during the regular solidification process. Furthermore, the DTA, SEM and XRD results reveal that no reaction occurs between the TiB2 particulate and matrix alloy during the partial remelting process, which indicates that TiB2 particulate is thermodynamically stable at the Mg-11Al-0.5Zn matrix alloy. (C) 2004 Elsevier B.V. All rights reserved.