Effect of Mg Addition on the Foaming Behaviour of AlSi7 Based Alloy Prepared by Powder Metallurgy Method

The effects of high Mg addition (2 wt%, 4 wt% and 6 wt%) on the foaming behavior of AlSi7 based alloys were researched. The results show that Mg can react with Al2O3 phase and Si element, and then the produced MgAl2O4 phase which has a good wettability with Al melt and Mg2Si phase are formed. Both of them can uniformly distribute in the alloy and induce a particle based stabilization mechanism, which can significantly reduce the negative impact of gravity drainage and capillarity. High Mg content can also change the pores formation in early stage, as a result, the pores grow and nucleate in a pool of liquid in a fairly spherical way. Therefore, a high expansion rate and good pore structures can be obtained. The disadvantage of high Mg content is the decrease of surface tension which makes pores easy to bust. A good trade-off between the beneficial and adverse effects of Mg content is 4 wt% for AlSi7 based alloy