Influence of yttrium additions on the hot tearing susceptibility of magnesium-zinc alloys

The influence of Y additions on the hot tearing behaviour of Mg-Zn alloys was investigated in this study. In permanent mould castings and in direct chill cast ingots, alloying of a few wt.% Y results in a significant reduction of hot tearing susceptibility. The reduced susceptibility is attributed to the effect of Y on the solidification path at the terminal period of solidification: it increases the solidus temperature and thus shortens the solidification path, which in turn reduces the terminal freezing range. Via thermodynamic calculations it is shown that this is caused by the formation of the ternary phase Mg3YZn6. Using a simplified version of Clyne and Davies' model, the influence of the terminal freezing range on hot tearing susceptibility is clearly illustrated. (C) 2010 Elsevier B.V. All rights reserved.