The tensile specimens were heat
treated using a T61 treatment and solution heat treated at a tempera- ture of 1,004F (540C) for 4 hours, followed by a quench in water at 122-140F (50-60C). The specimens were held for 24 hours at room temperature and then were aged at 320F (160C) for 6 hours. Out of the 20 specimens cast, 10 were randomly selected and tested using the ASTM E8 standard. The second experiment was the
fading set of experiment. A356.2 with Ca-Si-Ba additions of 200 ppm
3
of barium (224 ppm of calcium) was held at 1,391F (755C) for 24 hours. Optical emission spectroscopy and metallography samples, using the modified B108 mold, were cast at 0 minutes, 30 minutes, 1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 10 hours and 24 hours. Sets of five modified B108 castings were cast after 2 hours, 6 hours and 24 hours to evaluate the evolution of mechanical properties. T e last experiment was the remelt-
ing experiment. An A356.2 melt charge of 264.6 lbs. (120 kg) with 200
ppm of barium added (224ppm of calcium) was prepared (Melt 1). Ten ASTM B108 molds were cast out of melt 1. T e rest of melt 1 was cast into ingots to be remelted (remelting 1). Ten ASTM B108 molds were cast from remelting 1. T e rest of remelt- ing 1 was cast into ingots (remelting 2) to be remelted again. Ten ASTM molds were cast from remelting 2. T e same degassing and casting procedure that was mentioned before was used again with the exception that no wait- ing time for dissolution was used for remelting 1 and remelting 2.
Results and Conclusions
The experiment of using pure A356.2 without any addition resulted in a completely unmodified microstructure (level of modifica- tion 1 from AFS rating), as can be observed
by the coarse and angular eutectic silicon in Fig. 2. Following additions of phosphorus with the barium
and calcium, there was a small to negligible effect on the contamination of the modification. For addi- tions of 50 ppm of barium (56 ppm of calcium) with 30 ppm of phosphorus, a fully modified microstruc- ture is obtained (level 4). The same can be noted for larger additions of barium and calcium with additions of phosphorus (Figs. 3–4). This demonstrates that barium and calcium through Ca-Si-Ba additions are not susceptible to phosphorus contamination and as thus, they can act as a viable replacement for stron- tium additions. While the yield strength and ultimate tensile
strength values do not vary much, elongation mea- surements varied significantly. As expected, pure A356.2 presented a lower elongation with an average of 3.85%. This shows the effect of the angular and coarse silicon eutectic. With the 50 ppm of barium addition experiment, the 6.34% elongation is simi- lar or greater than what can be obtained in a higher concentration of Ca-Si-Ba additions. However, when 30 ppm of phosphorus is added, elongation drops to 4.93%. This indicates that even though a fully modi- fied microstructure is obtained, the phosphorus still negatively affects the mechanical properties. However, this effect disappears for additions of barium of 100 ppm and more. For higher additions of barium than 100 ppm and 112 ppm of calcium, there is no differ- ence in elongation between the different experiments. An ANOVA test was used to compare the different
results for experiments with additions of 150 ppm of strontium without barium/calcium and experiments
with additions of barium higher than 100 ppm with and without phosphorus additions. No significant differences between the different means could be observed (ANOVA (F (6,64)=1.36, p=0.24)). This signifies that when using additions of 100 ppm of barium and 112 ppm of calcium
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