Experimental method for segregation behavior of impurity elements in large wheel hub by reverse squeeze casting

The test material is A356 aluminum alloy, and its chemical composition is controlled according to American Standard b108-03a. A heavy truck hub with a nominal diameter of 500mm and a maximum wall thickness of 40mm was obtained by squeeze casting with vertical direct pressure reverse filling method, as shown in Fig. 1, and as shown in Fig. 2. The main process parameters of squeeze casting are as follows: pouring temperature is 690 ℃, specific pressure is 100MPa, starting pressure time is 15s, holding pressure for 1min.

Three wheels of the same batch were randomly selected for anatomical sampling. The sampling method is as follows: take 3 longitudinal sections symmetrically along the same circle, and take 8 30mm longitudinal sections on each longitudinal section according to the position shown in Fig. 2 × 30mm sample, corresponding to the number 1 ~ 8 position, the physical meaning of each position is: the number 1 position is the center under the punch (indenter), called the wheel center; Position 2 and position 3 are respectively 1 / 2 and 3 / 4 of the punch radius, which are located on the spoke plate of the hub and are the channel position for horizontal flow; Position 4 is the outer rim position with the thinnest wall, which is the first position to solidify, and mainly solidifies under gravity; Position 5 is the beginning of the gap formed by punch and die (the intersection of rim and spoke), which is the beginning of reverse filling; Position 6 and position 7 are 1 / 5 and 1 / 3 of the rim height respectively, which are the channel positions for reverse filling; Position 8 is the uppermost part of the rim, and the inner rim position is the farthest end of the reverse filling.

After the surface of each sample is removed by 5mm by cutting, the plane formed is used as the detection surface. The content of each element was detected by spark labm11 direct reading spectrometer, and the average value was taken as the content of each element; The average value of each element content of three sections with the same physical meaning along the circumference is taken as the composition at 1-8 above.

Because the basic content of different elements is different, some even have order of magnitude differences. In order to quantitatively express the segregation degree of each element, a dimensionless segregation ratio is used to reflect the segregation degree of each element. The segregation ratio is defined as the ratio of the maximum content to the minimum content difference and the average content of each element ψ w、 ψ r、 ψ H segregation ratio can quantitatively express the segregation degree of the whole casting, radial and longitudinal respectively.

Where, CW max, CW min, Cr max, Cr min, ch Max and CH min are the maximum and minimum contents of each element in the whole casting, the maximum and minimum contents in radial direction and the maximum and minimum contents in longitudinal direction respectively; CW, Cr and CH are the average contents of the whole casting, radial and height direction respectively. The segregation position is defined as the position where the deviation between the impurity element content and the average content is the largest.