Yuan Xiaoguang

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

Abstract 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

Analysis of principle deviation of subpixel Zernike moments operator

In original Zernike moments subpixel edge operator, ideal step edge model is chosen for calculating four parameters of a pixel point, and therefore principle deviation is caused by edge model. In order to discuss the effect of principle deviation on edge location, sampled edge model is chosen for calculating edge parameters, principle deviation of edge translation l is derived based on Zernike moments edge detection theory, and modified formula of l is given for Zernike moments operator with masks of 5 × 5 size. Both theory analysis and testing result demonstrate that principle deviation is zero when edge translation l is limited in central pixel of a sampled window. In another case, the modification of l should be considered, which results in edge location accuracy of non-subpixel level for this subpixel edge operator.