Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys
Abstract
:1. Introduction
2. Materials and Methods
3. Results and Discussion
3.1. Eutectic Area within the Melt Pool
3.2. Silicon Fiber Refinement within the Melt Pool
3.3. Cooling Rate in the Melt Pools
4. Conclusions
- Microstructures in the melt pools in the laser surface remelted arc-cast hypereutectic Al-20Si, Al-20Si-0.2Sr and Al-20Si-0.2Ce alloys comprised of mixtures of fully eutectic and hypoeutectic (primary Al dendrites and inter-dendritic eutectic). Eutectic regions in LSR Al-20Si alloy contained approximately 18 wt.% Si, which is higher than the equilibrium eutectic composition.
- The Si fibers in the eutectic microstructures of LSR Al-20Si alloys were reduced from a few microns in as-cast to less than 50 nanometers with rapid solidification and rare earth modification. Minimum average silicon fiber sizes in Al-20Si-0.2Ce were observed to be 35 ± 8 nm.
- Si fibers in the regular eutectic structure were found to be more refined towards the top of the melt pool.
- The volume fraction of the fully eutectic morphology in the melt pool depended on the cooling rate. Cooling rates for different experiments were calculated using the Eagar-Tsai approach and 104 K/s was found to be the optimal value to maximize the volume fraction of the fully eutectic morphology in the melt pool.
- The average area percentage of fully eutectic colonies in the melt pool in the investigated Al-20Si, Al-20Si-0.2Sr and Al-20Si-0.2Ce alloys decreased from ≈60% to ≈10% with increasing undercooling, ΔT, from ≈10 K to ≈50 K.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Appendix A
Experiment Number | Power (W) | Scanning Speed (mm/s) | Laser Beam Diameter (mm) |
---|---|---|---|
1 | 187.5 | 25.4 | 0.4 |
2 | 375.0 | 25.4 | 0.4 |
3 | 562.5 | 25.4 | 0.4 |
4 | 187.5 | 101.6 | 0.4 |
5 | 375.0 | 101.6 | 0.4 |
6 | 562.5 | 101.6 | 0.4 |
7 | 187.5 | 177.8 | 0.4 |
8 | 375.0 | 177.8 | 0.4 |
9 | 562.5 | 177.8 | 0.4 |
10 | 750.0 | 25.4 | 2 |
11 | 1500.0 | 25.4 | 2 |
12 | 2250.0 | 25.4 | 2 |
13 | 750.0 | 101.6 | 2 |
14 | 1500.0 | 101.6 | 2 |
15 | 2250.0 | 101.6 | 2 |
16 | 750.0 | 177.8 | 2 |
17 | 1500.0 | 177.8 | 2 |
18 | 2250.0 | 177.8 | 2 |
Experiment Number | Eutectic Formation of Al-20Si | Eutectic Formation of Al-20Si-0.2Ce | Eutectic Formation of Al-20Si-0.2Sr | |||
---|---|---|---|---|---|---|
Total Area (in μm2) | Percentage | Total Area (in μm2) | Percentage | Total Area (in μm2) | Percentage | |
1 | 3502.0 | 32.47% | 2983.5 | 26.91% | 11,269.5 | 54.58% |
2 | 25,528.6 | 71.51% | 6777.5 | 21.00% | 50,978.1 | 93.50% |
3 | 50,436.0 | 65.61% | 6814.3 | 11.11% | 85,823.7 | 72.33% |
4 | 301.0 | 2.97% | 206.4 | 1.98% | 304.9 | 1.82% |
5 | 682.3 | 2.42% | 0.0 | 0.00% | 5696.0 | 10.19% |
6 | 2339.1 | 5.05% | 273.5 | 0.54% | 27,124.3 | 28.70% |
7 | 1525.2 | 14.16% | 183.6 | 1.59% | 988.2 | 6.40% |
8 | 2157.5 | 7.59% | 0.0 | 0.00% | 0.0 | 0.00% |
9 | 10,707.5 | 24.72% | 0.0 | 0.00% | 6246.7 | 8.04% |
10 | 38,384.2 | 20.27% | 58,671.0 | 12.19% | 74,450.3 | 12.26% |
11 | 421,665.5 | 33.60% | 376,566.2 | 29.29% | 319,443.3 | 27.84% |
12 | 116,915.8 | 7.82% | 104,641.0 | 7.88% | 223,802.7 | 17.97% |
13 | 1576.3 | 2.97% | 23,519.3 | 3.80% | 24,559.2 | 14.63% |
14 | 212,394.3 | 37.03% | 36,856.2 | 5.27% | 88,232.0 | 14.15% |
15 | 154,943.6 | 16.95% | 0.0 | 0.00% | 44,948.5 | 5.96% |
16 | 0.0 | 0.00% | 31,319.8 | 7.54% | 0.0 | 0.00% |
17 | 92,172.6 | 20.27% | 264,627.0 | 22.32% | 42,871.2 | 9.95% |
18 | 218,353.0 | 28.97% | 41,944.9 | 6.05% | 248,621.5 | 34.33% |
Symbol | Explanation | Notes |
---|---|---|
a | Thermal diffusivity | |
Cc | Specific heat | |
G | Green’s function | |
k | Thermal conductivity | |
n | Operating parameters | |
q | Net heat input per unit time | (Power) |
Q | Power distribution | |
Q* | Heat source moving with v speed | |
R | Distance to the center of arc | |
R* | Dimensionless distance from the center of the arc | |
T | Temperature | |
Ambient temperature | ||
Critical temperature | ||
u | Dimensionless distribution parameter | |
v | Travel speed of arc | |
w | Distance in x direction in a moving coordinate of speed v | |
y | Y distance | |
z | Z distance | |
Distribution parameter for beam | ||
Density | ||
Incremental amount of heat | ||
Dimensionless time | ||
Dimensionless temperature | ||
Dimensionless distance in the moving coordinate | ||
dimensionless distance y | ||
dimensionless distance z | ||
∞ | infinity |
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Laser Spot Diameter (mm) | Average Fully Eutectic Area Percentage for Al-20Si-0.2Sr | Average Fully Eutectic Area Percentage for Al-20Si-0.2Ce | Average Fully Eutectic Percentage for Al-20Si |
---|---|---|---|
0.4 | 24.93% | 7.60% | 17.62% |
2 | 16.21% | 14.06% | 20.83% |
Experiment # | Cooling Rate (K/s) | Average Eutectic Formation | Std Dev for Eutectic Formation |
---|---|---|---|
1 | 1.80 × 104 | 37.98% | 12.89% |
2 | 6.78 × 104 | 62.00% | 8.28% |
3 | 4.15 × 104 | 49.67% | 9.86% |
11 | 1.16 × 104 | 30.24% | 3.86% |
17 | 9.30 × 104 | 17.52% | 4.40% |
18 | 7.74 × 104 | 23.12% | 13.47% |
6 | 1.57 × 105 | 11.43% | 15.13% |
9 | 2.00 × 105 | 10.92% | 12.61% |
13 | 8.15 × 105 | 7.13% | 6.51% |
15 | 1.12 × 105 | 7.64% | 8.60% |
Experiment # | LOG10 Scale Cooling Rate (K/s) | Vmax (mm/s) | G (K/mm) | Calc. Undercooling ΔTk (K) |
---|---|---|---|---|
1 | 4.3 | 25.4 | 708.7 | 18.1 |
2 | 4.8 | 25.4 | 2667.3 | 13.9 |
3 | 4.6 | 25.4 | 1634.4 | 15.3 |
6 | 5.2 | 101.6 | 1542.8 | 31.0 |
9 | 5.3 | 177.8 | 1174.2 | 43.4 |
11 | 4.1 | 25.4 | 457.2 | 19.8 |
13 | 3.9 | 101.6 | 86.1 | 55.3 |
15 | 5.0 | 101.6 | 1102.4 | 33.2 |
17 | 5.0 | 177.8 | 523.2 | 51.0 |
18 | 4.9 | 177.8 | 435.1 | 52.9 |
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Kayitmazbatir, M.; Lien, H.-H.; Mazumder, J.; Wang, J.; Misra, A. Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys. Crystals 2022, 12, 750. https://doi.org/10.3390/cryst12050750
Kayitmazbatir M, Lien H-H, Mazumder J, Wang J, Misra A. Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys. Crystals. 2022; 12(5):750. https://doi.org/10.3390/cryst12050750
Chicago/Turabian StyleKayitmazbatir, Metin, Huai-Hsun Lien, Jyoti Mazumder, Jian Wang, and Amit Misra. 2022. "Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys" Crystals 12, no. 5: 750. https://doi.org/10.3390/cryst12050750