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temperature) on the tensile properties of the casting were exam- ined. For each of the four unique conditions, five castings were created. Table 1 shows the process parameters used in the DOE.


Flat tensile samples were cut and milled from six specific locations in each casting (Figure 1). Due to a lack of avail- able area on the casting, the ASTM E8-01 sub-sized tensile bar was selected.


Prior to testing, the samples were X-rayed at the Ford Non- Destructive Evaluation facility in Livonia, Michigan. Testing was again conducted in accordance to the procedures outlined in ASTM E8-01. For these samples, the testing was conduct- ed on an MTS Sintech 30/G load frame equipped with a Re- newTM


Interface Works 4.0 data acquisition software system.


Microstructural examination was performed on a total of 13 fractured samples; these samples represented a range of locations and elongation-to-failure values. Metallographic sections were taken a short distance (3–4 mm) below the fracture surfaces on the tensile specimens. These sections were mounted parallel to the thickness direction, polished using standard metallographic techniques, and etched with an acetic glycol etch. Micrographs were taken using a Nikon EpiphotTM


inverted microscope.


Measurements of cell size, ESC size, and porosity were per- formed using the ImageProPlusTM


image analysis software;


at 100x magnification. The distribution of porosity was also quantified using a linear intercept method over the cross- section of each tensile sample.


To classify the type of porosity present, the metallographic samples were then carbon-coated and examined using a JEOL 840A SEMTM


equipped with an Oxford ISISTM X-ray


analysis system. For bulk porosity measurements, sections from directly behind the fracture surface were taken from 51 fractured tensile samples that had failed in the gage length due to porosity. The bulk porosity was then determined using Archime- des’ Method; the fluid used was laboratory water and the theo- retical density of the AM50 alloy was assumed to be 1.775 g/cm3


. Table 2. Elongation-to-Failure Values for AM50 HPDC Castings #9


results Mechanical Properties


The mechanical property results from the castings are present- ed in Table 2 and in Figures 2-4. Table 2 shows the elonga- tion-to-failure data as a function of processing condition and sample location. As this table shows, there are statistically- significant differences in the failure strain based upon sam- pling location for a given processing condition. However, this data also indicates that there are no discernible differences in elongation for a given sample location under different pro- cessing conditions. Therefore, either the processing condi- tions chosen (fast shot speed and oil temperature) were not the significant factors that influenced the failure strain or the factor levels chosen for these two parameters were too narrow to create a measurable difference.


#2 #6 #1


#3 #4


Figure 1. The tensile specimen locations in the “Ladder” Casting are shown. (Note: Areas shown in yellow illustrate the gating used during the casting process.)


Table 1. Processing Conditions used DOE for AM50 HPDC Castings


* Slow shot speed held constant at 0.1 m/sec. and melt temperature held constant at 680°C for all 20 castings. **Data presented as Average +/- 1 Standard Deviation.


18 International Journal of Metalcasting/Winter 2012


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