Figure 7 is the thermal data obtained during solidification of the various alloys in Table 2. In Figure 7, it can be seen
that the point B for 2024C1 and 2024C2 are below TL1 and that for 2024C3 is above, predicting that 2024C1 and 2024C2 would yield a favorable non-dendritic morphol- ogy and this has been confirmed by the microstructures in Figure 6(a) and (b), respectively. Further, comparing Fig- ure 7 and Figure 6, 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 morphol- ogy of the primary Al phase in the as-cast microstructure. It shall be noted that point B could not be lowered indefi- nitely because of the loss of feasibility to shape cast the alloy in the tilt-pour casting process.
Alloy 6082
The procedure for optimization of alloy com- positions and melt temperatures for Alloy 6082 was similar to that described in Figure 2 and that was used for optimization of Alloy 2024. A mass ratio, mr
= 6, was initially assumed and
(99F). Hence, a mass ratio, mr = 55C (99F). At mr
(= TL1 –TL2
an investigation of the isopleths of the respec- tive alloy multi-component phase diagrams re- vealed that ∆TL
of Alloy 1 was mixed into 30 grams of Alloy 2 to obtain 330 grams of Alloy 3 (6082). Visual- ization of solidification paths of Alloy 1, Alloy 2 and Alloy 3 was not possible in one isopleth from the Al-Mg-Si-Mn phase diagram. Figure 8 shows three isopleths from the multi-compo- nent phase diagrams showing the average com- positions of Alloy 1 (Figure 8a), Alloy 2 (Fig- ure 8b) and Alloy 3 (Figure 8c) for the Alloy 6082. Table 3 shows the alloy notations and values of various variables used for the CDS
sumed and this proved beneficial with a mea- sured ∆TL
= 10, 300 grams
) was less than 55C = 10 was as-
experiments. A procedure similar to that described to cast 2024CC was also used to obtain conventional cast- ing sample 6082CC.
Figure 9 shows that the most favorable microstructure for CDS process of 6082 alloys is obtained with the conditions for 6082C1. The microstructure of 6082C2 was nearly favor- able and those of 6082C3 and 6082CC were unfavorable for a successful CDS process of Alloy 6082. Figure 10 shows the thermal data obtained during solidification of Alloy 3 (6082) under various conditions shown in Table 3. In Figure 10, it can be observed that point B of 6082C1 is below the liquidus temperature TL1,
and those for 6082C2, 6082C3 and 6082CC are above. The thermal data in Figure 10 predicts that 6082C1 will be the most favorable among the alloys for the CDS pro- cess as validated by the microstructures in Figure 9.
Time (s)
Figure 7. Thermal data obtained during solidification of 2024C1, 2024C2, 2024C3 and 2024CC as shown in Table 2.
Table 3. Variables used in CDS experiments to Cast 6082 Al Wrought Alloy
International Journal of Metalcasting/Spring 11
49
Temperature (ºC)
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