because the samples broke instantaneously after starting the tensile test. The alloy 2024T particularly showed a poor response to heat treatment as compared to alloys 6082T and 7075T, because in Table 6, the copper content of al- loy 2024T was 5.7 wt% which is higher than the nominal copper allowance (shown in Table 1), and this could be a reason for the poor response to heat treatment by this alloy in Table 8. Further, the heat treatment tempers for these alloys were selected from the literature5,6
of Al wrought al-
loy processing which may not be suitable for heat treating shape castings because the microstructure and phase for- mation in a shape cast alloy would be vastly different from those in components that underwent solid-state processing such as forging, extrusion and rolling. Significant improve- ments are possible in the CDS process, alloy composition selection and heat treatment cycles will enable maximizing the tensile properties of these alloys.
The CDS technology used in these tilt-pour casting trials was crude with minimum control over the melt cleanliness and prevention of inclusions and artifacts during the manual
Figure 20. Typical thermal data obtained from the pouring cup during the tilt-pour casting trials of 6082T samples. The data reflects the regions before, during and after the mixing process in CDS for this alloy.
(a)
(b)
Figure 21. Typical microstructure of the gauge section of tensile bars for 7075 Al alloy (a) 7075T showing non-dendritic primary phase and (b) 7075TC showing dendritic primary phase. Two rosette shaped grains are highlighted by arrows in (a).
(a)
(b)
Figure 22. Typical SEM images of fracture surface of the tensile bar cross-section after the testing. (a) 7075T sample showing a reasonable clean and compact structure, (b) 7075TC sample with numerous voids shown by the definition of the dendrites and lack of soundness.
International Journal of Metalcasting/Spring 11 57
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 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88