2. At this mass ratio, 300 grams of Alloy 1 was mixed into 50 grams of Alloy 2 to obtain 350 grams of Alloy 3 (7075). Visualization of the solidification paths of Alloy 1, Alloy 2 and Alloy 3 was not possible in one isopleth of the Al-Zn- Cu-Mg phase diagram. Figure 11 shows three isopleths of various multi-component phase diagrams showing the av- erage compositions of Alloy 1 (Figure 8a), Alloy 2 (Figure 11b) and Alloy 3 (Figure 11c) for the Alloy 7075. Table 4 shows the notations and values of various variables used for the CDS experiments of Alloy 7075. A procedure simi- lar to that used to cast 2024CC and 6082CC was also used to obtain conventional casting sample 7075CC (Table 4).
In Figure 12, (a), (b), (c) and (d) are typical microstructures of 7075C1, 7075C2, 7075C3 and 7075CC (Table 4), re- spectively. It can be observed that the 7075C1 and 7075C2 samples show a favorable non-dendritic morphology of the primary Al phase in Figure 12(a) and (b), respectively. Figure 12(c) shows that 7075C3 is partially dendritic with regions of rosette and dendritic morphologies, respectively in the microstructure. Figure 12(d) shows the unfavorable dendritic morphology of the primary phase in 7075CC al- loy samples.
Mass Fraction of Mg
for 7075C3 is above, thus predicting that conditions for 7075C1 and 7075C2 should be favorable for CDS as con- firmed by the microstructures in Figure 12. Further, com- paring Figure 12 and Figure 13, it can be hypothesized that the lower the point B in the thermal data obtained during mixing of the pre-cursor alloys, the more equiaxed is the morphology of the primary Al phase in the as-cast microstructure.
Figure 13 presents the thermal data obtained during so- lidification of 7075C1, 7075C2, 7075C3 and 7075CC alloys. In Figure 13, it can be seen that the point B (in Figure 1), for 7075C1 and 7075C2 are below TL1
and that (b)
Tilt-Pour Shaped Casting Trials
The observations and results from the experiments in the previous sub-section were used to design, optimize and shape cast the 2024, 6082 and 7075 Al wrought alloys into test bars for mechanical property evaluation in tilt- pour casting equipment. Table 5 presents the variables used in the tilt-pour casting trials of the three alloys in
(a)
Mass Fraction of Zn (c)
Mass Fraction of Zn Time (s)
Figure 10. Thermal data obtained during solidification of 6082C1, 6082C2, 6082C3 and 6082CC as shown in Table 3.
International Journal of Metalcasting/Spring 11
Figure 11. Three Isopleths from the Al-Zn-Cu-Mg Phase Diagram showing the average compositions of (a) Alloy 1, (b) Alloy 2 and (c)Alloy 3 (7075).
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Temperature (ºC)
Temperature (ºC)
Temperature (ºC)
Temperature (ºC)
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