for the tensile data of each of the two test conditions are shown in Table 7. It is important to note the averages of each set of tensile data were nearly identical; the un- treated condition in Table 7 corresponded to the metal in Fig. 12(a), and the treated condition corresponded to the rotary degassed metal shown in Figure 12(b). The data presented overlaid with the model true-stress–true strain flow curve is presented in Fig. 13, and the corresponding quality chart is presented in Fig. 14.


On first examination, considering only the mean values presented in Table 7, it would seem that there was little


or no benefit in rotary degassing of the molten metal. This would appear to be a very surprising result and not con- sistent with what is known about the advantages of degas- sing molten metal. One important observation was that there was no increase in the upper bounds of the data set corresponding to the treated (degassed) metal. This tends to suggest that hydrogen did not have an adverse effect in the current sample geometry, since if it did, it would be expected that an overall improvement would be observed in the treated metal, similar to the differences seen be- tween melt velocities of 26 and 82 m/s. It may however be likely that, in thicker sections, hydrogen would have a


Table 7. Data for Alloy 4 Samples Produced from Recycled Metal, either a) Untreated, or b) Treated by Degassing with High Purity Argon


Figure 12. Reduced pressure tests for (a), as-melted alloy, untreated, ρ = 2.39g/cm3. (b), rotary degassed alloy, ρ = 2.74g/ cm3. (c), as (b) +16h hold before taking sample; ρ = 2.5g/cm3


. Sample diameter was 5cm at the base. 50 International Journal of Metalcasting/Summer 2011


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