to ascertain casting quality. The gross weight of the ejected cast component was approximately 900 grams. Subsequent to casting the samples, the test bars were machined out of the casting and microstructural analysis was carried out in a sample sectioned from the gauge length in one of the cast tensile bars. Five samples each were set aside for tensile property assessment in each of the three tempers (F, T4 and T6), respectively. For each and every tilt-pour casting trial, a K-type thermocouple was inserted in the pouring cup to continuously monitor the melt temperatures before, during and after the mixing process in CDS.
The resultant castings were deemed successful and sound when the following was achieved:
• No visual hot-cracking or hot-tearing on the cast component.
• No visual shrinkage or defect feature on the surface of the cast test bars.
• Non-dendritic morphology of the primary Al phase in the microstructure obtained from the cross-sec- tion of the gauge in the tensile test bar.
• Reasonable tensile properties of the as-cast samples. • Reasonably compact features in the optical low magnification micrograph of the fracture surface of the tensile bars.
Commercial purity raw materials were used in prepar- ing all of the alloy compositions in this study. All com- positions presented in this study were given in weight percentage of the respective solute element. Table 1 presents the nominal compositions of the three alloys used in this study.
Results and Discussion
The results of this study are presented in the following format for each alloy:
• Optimization of the Precursor Alloys • Tilt-Pour Shaped Casting Trials • Foundry Returns Management
Optimization of the Precursor Alloys
In this section the optimization of the precursor alloy compositions and temperatures, as shown in Figure 2, are presented for each of the three alloys in this study.
Mass Fraction of Cu
Figure 5. Isopleth of Al-Cu-Mg Phase Diagram showing the optimum average compositions of Alloy 1, Alloy 2 and Alloy 3 to cast 2024 aluminum alloy by CDS process.
Table 1. Nominal Composition (Weight %) of 2004, 6082 and 7075
Alloy 2024 For Alloy 2024, an initial mass ratio, mr = 6 was selected.
The required weight of Alloy 2024 (Alloy 3) was 350 grams as dictated by the crucible size and the density of Alloy 2024. Hence, m1
and 543C (1009F), respectively. The difference between the two liquidus temperatures, TL1
and TL2
selected for Alloy 1 as 653C (1207F), 666C (1231F) and 676C (1249F) for optimization. Table 2 shows the notations and optimized precursor alloy compositions in addition to the various process variables used temperature optimization stage of the CDS experiments of Al wrought Alloy 2024.
which is greater than the prescribed 55C (99F) in Figure 2. The three superheat melt temperatures, T1
were measured to be 651C (1207F) and TL2
was 108C (194.4F) above TL1
were
For conventional casting experiments approximately 350 grams of Alloy 2024 (Alloy 3) was melted and solidified as described by the procedure in the section titled ‘methodolo- gy’ in this manuscript. All conventional casting experiments have the notation CC (Conventional Casting) following the respective alloy code in Table 2.
favorable isopleth from the Al-Cu-Mg phase diagram was simulated and shown in Figure 5 wherein all the three alloy compositions could be visualized. The values of the liquidus temperatures TL1
was 300 grams and m2 was 50 grams. A
International Journal of Metalcasting/Spring 11
47
Temperature (ºC)
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