in Figure 6, and only one casting existed for each composi- tion to supply mechanical test samples.
Component Casting-Engine Block—Stage 2
Once analysis of the wedge castings was completed, on two of the four alloys which rendered the highest and lowest dispersed porosity, they were then cast into the V8 engine block cast- ings. In order to provide complete filling of the zircon engine block sand package, the melt temperature was adjusted to 760C (1400F), and the degassed melt rendering a density of 2.70g/ cc for the RPT test samples was used as the minimum density.
analysis were performed on the tensile test bars at the gripped end. See the location of the reduced gauge section of test bars in Figure 9b. The 49 analytical fields and the mag- nification 50X is indicated in Figure 7 for the wedge casting.
The metallurgical process flow, testing and analysis of the com- ponent engine block are shown in Figure 1 as Stage 2. The heat treatment used following the Thermal Sand Removal (TSR) operation had the same parameters for both the wedge castings and the U328 engine blocks. However, the quench rate after the solution stage is not known as the engine block is quenched in water (held at 90C) for a total of 5 minutes before entering the age furnace. After heat treatment, the castings were sectioned to extract the inner bulkhead sections. Figure 9a shows the V8 en- gine block and the five bulkheads. The inner bulkhead sections solidified more slowly than the front and the rear bulkheads (A & E) therefore they have a coarser structure than the front and rear ones. In addition, the inner bulkheads sustain the highest cyclic stress during the engine running operation. Both tensile and fatigue test samples were extracted from bulkheads B, C and D as shown in Figure 9a. PAF porosity, largest pore diam- eter and λ2
Vickers microhardness was performed on the metallographic test samples after completion of image analysis.
Elevated Temperature Fatigue Testing— Wedge & Engine Block Castings
The fatigue test samples were tested using a fully reversed (R = -1, defined as σmin
of 40Hz. The fatigue test temperature of 120C (248 F) was maintained using an environmental temperature chamber that housed the high temperature grips. Forty minutes were required to ramp the test sample and grips to 120C (248 F) prior to the test. The fatigue test samples were tested in compliance with the ASTM E-466-96 protocol using the Instron 8801 machine.
/σmax
Due to the limited number of wedge castings, seven fatigue test samples were extracted for each composition cast, and were tested at a single stress level of 105 MPa. Preliminary testing indicated that this stress level resulted in failure ev- ery time. The number of cycles until failure was plotted in sequence from the highest to the lowest ones.
The staircase, or “up and down” method, originally intro- duced by Dixon & Mood27
was used for the fatigue testing of ) sinusoidal axial profile at a frequency
Figure 9a. Component engine block casting with bulkhead sections indicated.
International Journal of Metalcasting/Fall 10
Figure 9b. Location of the fatigue and tensile test bars taken from bulkheads B, C and D.
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