Fig. 5. Solidification paths for Al-5% Si alloys are plotted.
Fig. 6. Solidification paths for Al-9% alloys are plotted.
researchers calculated solidifica- tion paths for numerous silicon contents. In this way they derived a map of safe iron contents for their casting (Fig. 8). The results of related research,
conducted by Caceres and co- workers, should also be consid- ered. They produced castings in a number of alloy compositions and measured mechanical properties. Some of their results are shown in Fig. 9, which illustrates the impor- tance of microsegregation during segregation, and how higher silicon contents may be used to advantage in Al-Si based alloy castings. The tensile strengths for cast- ings heat treated to the T6 tem- per are shown on a quality plot (Ultimate Tensile Strength [UTS]
versus the log of elongation). The red lines show constant val- ues of quality index (in MPa). The blue arrows indicate the change in alloy composition. For example, iron was added to alloy 1 to obtain alloy 2. The result was a significant loss in casting quality—about 120 MPa according to the quality index. Silicon was added to alloy 2 to
from alloys 1 → 6 → 7, except in this case copper was added along with the iron.
The loss in quality with the
combined addition of iron and copper was larger—about 200 Mpa—but that loss was regained by
obtain alloy 3. Nearly all of the lost quality was regained by increasing the silicon content from 4.5 to 9%. A similar result was found going
increasing the silicon content. By contrast, when copper was
added by itself; in the alloys 1 → 4 → 5, only a small loss of quality was found in alloy 4.
This article was based on Paper 13-1224, which was presented at the 117th Metalcasting Congress.
ONLINE RESOURCE
The B-F equations and data used to calcu- late solidification paths have been placed into Excel programs. You may download a few of these calculations by going to
www.moderncasting.com. The Excel programs make it easy to do your own calculations.
Fig. 8. A solidification map to avoid primary β is shown.
Fig. 9. The plot shows the properties of heat treated (T6) castings for seven different alloy compositions: (1) 4.5Si-1Cu-0Mg-0.2Fe; (2) 4.5Si-1Cu-0.1Mg-0.5Fe-0.25Mn; (3) 9Si-1Cu-0.1Mg-0.5Fe-0.25Mn; (4) 4.5Si-4Cu-0.1Mg-0.2Fe; (5) 9Si-4Cu-0.1Mg-0.2Fe (6) 4.5Si-4Cu-0.1Mg- 0.5Fe-0.25Mn; (7) 9Si-4Cu-0.1Mg-0.5Fe-0.25Mn.
38 | MODERN CASTING June 2014
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60