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Results and Discussion Metallography - Set 1


In this section, the microstructural analysis for two of the initial castings, B-F-710 and B-S-710, are presented and the effect of each result on the casting process and product qual- ity is discussed.


Density Plate density can be affected by air entrapment or turbulent flow, as well as solidification shrinkage leading to porosity formation, and measuring this property for each of the sam- ples in Figure 6 provides insight to void locations through- out the plate. Density was measured by an Archimedes prin- ciple-based instrument, which takes an initial measurement of the sample in air, then again after it is submerged in liquid (water). Table 5 lists the results of these measurements for plates of both filling profiles.


From the values displayed in the table above, it is seen the densities for both plates are in reasonable proximity of one an- other and in close range to the reference density7 m3


. In reference to void regions within the plate, the density


variation is representative of a 0.05-0.5% porosity range. This range of fractional porosity presents values well below those found in literature as a result of entrainment during filling.1 These small variations could be attributed to slight differences in feeding or cooling conditions as is reflected in the Dendrite Arm Spacing (DAS) data of the following section.


Secondary Dendrite Arm Spacing One method used to validate or calibrate filling simulations, without direct temperature measurements during casting, is the measurement of the secondary dendrite arm spacing (SDAS). Measurements were conducted on several of the slow and fast fill B plate samples referenced previously, so the data could be used to obtain cooling rate information for several locations within the plate by using known correla- tions of the SDAS for the A356 alloy. Table 6 lists the mean SDAS values obtained from the specimens.


Table 7. Measured Mean Values of Equivalent Pore Diameter of 2680 kg/


Porosity To perform a porosity characterization of the plate, an im- age analysis program for the optical microscope was cre- ated in order to obtain the required information listed in the Experimental Procedures section. Figure 10 shows a typical


Table 5. Density (kg/m3 ) for Fast and Slow Filled B Plates


Table 6. Mean Secondary Dendrite Arm Spacing in Slow and Fast Filled B Plates (mm)


Figure 10. Area section of sample containing a pore.


International Journal of Metalcasting/Spring 2012 73


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