The contents of impurity elements at different positions in A356 aluminum alloy wheel hub by reverse squeeze casting are shown in Table 1. It can be seen that there are certain differences in the content of each impurity element in different positions of the hub, that is, there are different degrees of macro segregation. According to table 1, the segregation ratio of each element in the whole hub can be obtained by further sorting, as shown in Table 2. It can be seen from table 2 that the segregation ratio of each impurity element is obviously different. The longitudinal segregation ratio ψ H is calculated by formula according to the data of positions 5, 6, 7 and 8; Radial segregation ratio ψ R is calculated from the content data of positions 1, 2, 3 and 5 according to the formula; Overall segregation ratio ψ W is calculated from the data of 1-8 points according to the formula. It can be seen from table 2 that the order of segregation degree of impurity elements is as follows:
According to the overall segregation ratio ψ The order of W is p > Zn > Pb > CA > Fe > Mn > Cu > Zr; According to longitudinal segregation ratio ψ The order of H is Zn > Pb > CA > Fe > Cu > P > Mn = Zr; According to radial segregation ratio ψ The order of R is Zn > P > Cu > Fe > CA > Pb > Mn > Zr.
It can be found that the order of segregation degree in different directions is not consistent. Cu with less overall segregation is the third with more serious segregation in radial sorting, while Pb with less overall segregation is the third with less segregation in radial sorting. It is found that the segregation degree of different elements is different in different directions except Zn is in the first place and Mn is in the last place. This shows that the segregation degree of each element can not be simply determined by the size of equilibrium distribution coefficient, but also needs to consider the influence of flow, density and other external factors.
It is convenient for engineering application to divide the segregation grade in small scale. Here, the degree of segregation is divided into four grades: [0 ~ 0.1] is grade 1, and there is no segregation basically（ 1 ~ 0.2] is grade 2, and the segregation is light（ 2 ~ 0.3] is grade 3, with heavy segregation（ 30 ~ 1.0] is grade 4, and the segregation is serious. See Table 3 for the segregation grade of impurity elements. It can be seen that the radial and vertical segregation levels of each element are slightly different, but the vertical segregation level is consistent with the overall segregation level. Zn, Pb and P belong to 4 levels, that is, serious segregation elements; CA belongs to the third order, that is, the elements with heavy segregation; The other impurity elements such as Fe, Cu, Mn and Zr are in grade 2, which belong to light segregation elements.
