Figure 15 shows typical optical micrographs showing the microstructure of the cross-section of the cast component obtained from the gauge of an as-cast tensile bar of Al Al- loy 2024. Figure 15(a) shows the microstructure for 2024T casting with the non-dendritic morphology of the primary Al phase and Figure 15(b) shows the dendritic morphology of the primary Al phase in a 2024TC casting with a distinct shrinkage porosity defect as expected in a conventional cast- ing of the wrought alloys. Figure 16 shows typical images of the fracture surface obtained on the tensile test bars after testing for 2024T and 2024TC samples. Figure 16 (a) shows a reasonable compact structure of 2024T sample with a nearly ductile fracture and no discernable dendritic structure could be observed. Figure 16 (b) shows a defective casting of 2024TC sample with several voids (porosity) evident from the clearly defined dendrites in the microstructure. Figure 17 shows the typical thermal data obtained from the pour- ing cup during the tilt-pour casting trials of Alloy 2024T. The data was obtained before, during and after the mixing process in the pouring cup. The thermal data in Figure 17 shows that point B lies well below the liquidus temperature, TL1
predicting a good CDS process.
Figure 18 shows typical optical micrographs showing the microstructure of the cross-section of the cast component obtained from the gauge of an as-cast tensile bar of Al Al- loy 6082. Figure 18(a) shows the microstructure for 6082T casting with the non-dendritic morphology of the primary Al phase with no discernable casting defect and Figure 18(b) shows the dendritic morphology of the primary Al phase in a 6082TC casting with a distinct shrinkage porosity defect as expected in a conventional casting of the wrought alloys. Figure 19 shows typical images of the fracture surface ob- tained on the tensile test bars after testing for 6082T and 6082TC samples. Figure 19 (a) and (b) show a reasonable compact structure of Alloy 6082T with a nearly ductile fracture and no discernable dendritic structure could be ob-
served. Figure 19 (c) and (d) show a defective casting of 6082TC sample with several voids (porosity) evident from the clearly defined dendrites in the microstructure. Figure 20 shows the typical thermal data obtained from the pour- ing cup during the tilt-pour casting trials of Alloy 6082T. The data was obtained before, during and after the mixing process in the pouring cup. The thermal data shows that the point B lies well below the liquidus temperature, TL1
predict- ing a good CDS process.
Figure 21 shows typical optical micrographs showing the microstructure of the cross-section of the cast component obtained from the gauge of an as-cast tensile bar of Al Al- loy 7075. Figure 21(a) shows the microstructure for 7075T casting with the non-dendritic morphology of the primary
Figure 17. Typical thermal data obtained from the pouring cup during the tilt-pour casting trials of 2024T samples. The data reflects the regions before, during and after the mixing process in CDS for this alloy.
Figure 18. Typical microstructure of the gauge section of tensile bars for 6082 Al alloy (a) 6082T and (b) 6082TC. (b)
(a) International Journal of Metalcasting/Spring 11 55
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