Applicability of Solid Solution Heat Treatments to Aluminum Foams
Abstract
:1. Introduction
2. Experimental Section
2.1. Preparation of Aluminum Foams
Diameter/Height (mm/mm) | Foams Density (kg·m−3) | Solid Cylinders | |||
---|---|---|---|---|---|
40/40 | 420 | 660 | 900 | 1200 | Yes |
50/50 | 670 | Yes | |||
60/60 | 650 | Yes | |||
70/70 | 690 | Yes |
2.2. Mesoscale Density Analysis
2.3. Heat Treatment and Temperature Measurement
- The specimen is introduced into a pre-heated furnace at 530 °C for 2 h, allowing the solid solution to be formed.
- Sample is extracted from the furnace and rapidly quenched in cold water (~25 °C). Thus, the previous state is stabilized at room temperature, obtaining a supersaturated solid solution. The sample is then kept for 72 h at room temperature in order to promote natural ageing.
- Lastly the sample is introduced into a pre-heated furnace at 175 °C for 10 h (artificial ageing) leading to the formation of precipitates in fine dispersion.
2.4. Heat Transfer Modeling
2.5. Microhardness Tests
3. Results and Discussion
3.1. Cellular Structure and Density Distribution
Diameter/Height (mm/mm) | Experimental density (kg·m−3) | Computed density (kg·m−3) | Percentage difference (%) |
---|---|---|---|
40/40 | 420 | 450 | +7.1 |
40/40 | 660 | 690 | +4.5 |
40/40 | 900 | 840 | −6.7 |
40/40 | 1200 | 1120 | −6.7 |
50/50 | 670 | 720 | +7.5 |
60/60 | 650 | 700 | +7.7 |
70/70 | 690 | 670 | −2.9 |
3.2. Temperature Evolution During the Quenching Process
3.2.1. Solid Cylinders
3.2.2. Foamed Cylinders
3.2.3. Average Cooling Velocities in the Critical Range
3.2.4. Water Ingression Inside the Foams
3.3. FEM Simulation
3.3.1. Solid Cylinders Verification
3.3.2. Heat Transfer Coefficients
3.3.3. Temperature Distribution and Temporal Evolution
3.3.4. Treatability
3.4. Microhardness Measurements
4. Conclusions
- The developed simulation model has been able to reproduce the experimental temperature evolution inside the foams during the quenching process. To this end, the model must consider the real density distribution -for example by using the SSDD methodology-, otherwise the temperature evolution could only be reproduced for the inner regions.
- The observed water infiltration during the quenching reveals the presence of defects –perforated cell walls– in the cellular structure that can clearly influence the process and should be considered in future modeling. This effect was not directly considered in the present FEM model but was overcome thanks to the IHCP iterative methodology used.
- The lower cooling rates exhibit by Al foams in comparison to solids can be explain in terms of: (i) The increased thermal resistance due to the lower density, the possible inhomogeneities in the inner structure and the small defects like cell wall cracks; (ii) The completely different boundary conditions in the case of foams due to the skin rugosity and internal defects (water infiltration through cracks in cell walls), that change the interface between the sample and the external medium. As a consequence of this, the calculated effective values for h, using the proposed model, have shown to be 3.5 to 6 times lower for aluminum foams (~1500 W/m2·K) in comparison to solid samples (~7000 W/m2·K).
- Both predictions and experimental data confirm the existence of certain limits for a complete treatment of foamed aluminum. In one of the studied cases (70/70 mm foam) it was possible to correlate the simulation predictions with the experimental microhardness profile, confirming the limit of 33 K/s in the critical temperature range for the selected alloy. Based on this, an extended prediction has been proposed for foams of different density and size.
Acknowledgments
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Lázaro, J.; Solórzano, E.; Escudero, J.; De Saja, J.A.; Rodríguez-Pérez, M. Applicability of Solid Solution Heat Treatments to Aluminum Foams. Metals 2012, 2, 508-528. https://doi.org/10.3390/met2040508
Lázaro J, Solórzano E, Escudero J, De Saja JA, Rodríguez-Pérez M. Applicability of Solid Solution Heat Treatments to Aluminum Foams. Metals. 2012; 2(4):508-528. https://doi.org/10.3390/met2040508
Chicago/Turabian StyleLázaro, Jaime, Eusebio Solórzano, Javier Escudero, Jose Antonio De Saja, and Miguel Rodríguez-Pérez. 2012. "Applicability of Solid Solution Heat Treatments to Aluminum Foams" Metals 2, no. 4: 508-528. https://doi.org/10.3390/met2040508