Heterogeneous nucleating role of TiB2 or AlP/TiB2 coupled compounds on primary Mg2Si in Al-Mg-Si alloys

Refinement and modification performance of Al-Ti-B master alloy alone or with Al-P master alloy on primary Mg2Si in Al-12.67% Mg-10.33% Si alloy was investigated in this paper. The experimental results show that perfect effect can be obtained after addition of 1% Al-5Ti-1B master alloy into the Al-Mg-Si alloy. The morphologies of primary Mg2Si Particulates change from dendritic to polygonal shape, and their average sizes decrease from similar to 100 to similar to 20 mu m. The ultimate tensile strength of the alloy increases. EPMA and TEM results show that TiB2 particles act as the nuclei of primary Mg2Si Crystal lattice correspondence indicates TiB2 has a good lattice matching coherence relationship with Mg2Si, and the disregistry is only 4.64%. Furthermore, the addition of Al-5Ti-1B master alloy can significantly improve the refinement and modification effect of AlP on primary Mg2Si. It is also found that coupling particles of AlP and TiB2 exist in the center of primary Mg2Si. (C) 2008 Elsevier B.V. All rights reserved.