Four relative defect ratings were defined to compare the de- fect levels for different casting processes according to the presences of different types of defects. The microporosity was not taken into account since it appears in all castings and had similar area percentages, as shown in Figure 6(a). The defect ratings were defined in the following manner Level 0: samples with no apparent defect (NAD); Level 1:
sample with only either a crack-like defect less than 2500 µm or sponge shrinkage with the average diameter less than 3000 µm; Level 2: samples with larger crack-like defect or sponge shrinkage, or with a gas pore less than 600 µm diameter; Lev- el 3: samples with gas pores larger than 600 µm and/or the sponge shrinkage larger than 3000 µm. The defects analysis for each casting group is summarized in Table 2. For squeeze
Table 1. Porosity Analysis Results for Each Casting Process
(a) Squeeze Cast
(b) LPPM
(c) T-Mag
(d) Ablation
Figure 8. Typical metallographic images for four different casting processes illustrate the different defects found during testing. (a) Squeeze Cast, (b) LPPM, (c) T-Mag, (d) Ablation.
International Journal of Metalcasting/Fall 2011 41
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