1. Overview:
- Title: Vacuum Rheocasting Heat Sinks with Significantly Improved Performance
- Authors: M. Hartlieb, J.-C. Tawil, S. Bergeron, F. Niklas
- Year of Publication: 2023
- Journal/Conference: NADCA (North American Die Casting Association) Die Casting Congress & Tabletop
2. Research Background:
The demand for heat sinks across various industries (e-mobility, telecommunications, electronics, etc.) is significantly increasing, along with stricter performance requirements. A primary requirement for heat sinks is high thermal conductivity. Pure aluminum exhibits excellent thermal conductivity (247 W/mK), but it's challenging to cast and possesses low strength. Typical die-casting alloys offer thermal conductivity in the range of 100-130 W/mK; permanent mold (PM) alloy A356-T6 shows approximately 150 W/mK, while 6000 series extrusions achieve 160-200 W/mK. Reducing silicon content enhances conductivity but compromises the ability to cast thin and intricate shapes (such as cooling fins) using High Pressure Die Casting (HPDC). Beyond thermal conductivity, maximizing heat dissipation necessitates maximizing surface area for heat transfer to the cooling medium. Designers aim for the highest number of long, thin fins arranged to maximize turbulence within the cooling medium, thereby enhancing heat evacuation from the heat sink's surface. Die-casting offers considerable advantages over PM casting or extrusion for such designs, enabling cost-effective production of intricate, thin-walled components in a single casting.
3. Research Objectives and Questions:
- Research Objective: To demonstrate a die-casting approach for producing heat sinks with significantly improved performance using high-vacuum rheocasting (Comptech process) and provide improved, economical, and sustainable solutions applicable to various industrial applications.
- Key Research Questions: Can high-vacuum rheocasting (Comptech process) produce heat sinks achieving a thermal conductivity exceeding 180 W/mK and a yield strength above 80 MPa?
- Research Hypothesis: High-vacuum rheocasting, combined with optimized alloy composition and heat treatment, will yield heat sinks surpassing the performance of conventional die-cast heat sinks in terms of both thermal conductivity and mechanical properties.
4. Research Methodology:
- Research Design: A Design of Experiments (DOE) approach was employed to investigate the influence of Si, Mg, Fe, and Mn content, along with heat treatment, on the mechanical properties and thermal conductivity of Rheocool® alloys.
- Data Collection Methods: Specimens were produced using Comptech rheocasting technology with a solid fraction of 25-45%. Heat treatment was conducted between 150 and 300°C. Thermal conductivity measurements were taken at room temperature, 50°C, and 100°C. Mechanical properties (yield strength, tensile strength, elongation, etc.) were also measured.
- Analytical Methods: Statistical analysis of experimental results was performed to determine optimal alloy composition and heat treatment parameters.
- Subjects and Scope: The study focused on Rheocool® alloys, examining the effects of varying Si, Mg, Fe, and Mn content and heat treatment on thermal conductivity and mechanical properties.
5. Major Research Findings:
- Key Findings: A thermal conductivity exceeding 180 W/mK at 100°C and a yield strength above 80 MPa were achieved by reducing Si content (to 1.8%), incorporating an optimal amount of Mg (0.26%), and employing T5 heat treatment. Adding Sr did not enhance high-temperature thermal conductivity. Manganese addition proved detrimental to thermal conductivity. The distance from the gate in the casting process also impacted thermal conductivity (Figure 2).
- Statistical/Qualitative Analysis Results: Figures 3 and 4 illustrate the impact of silicon content, Mg addition, and heat treatment on thermal conductivity and yield strength. Figure 5 compares yield strength across different alloy compositions. Results indicated that various factors, including solid fraction, design, gate location, and heat treatment, influenced thermal conductivity and mechanical properties.
- Data Interpretation: The study demonstrates the feasibility of producing heat sinks exceeding 180 W/mK thermal conductivity at 100°C and 80 MPa yield strength by utilizing low-silicon alloys (1.8% Si), appropriate Mg additions, and optimized heat treatment. Alloys with higher Si content (up to 3.5%) could also meet the target properties with optimized heat treatment and composition.
- Figure List and Description:
![Figure 1. Fin designs on heat sinks: left with all parallel fins, right with angled fins increasing turbulence in the air (cooling medium) and increasing air exchange between the fins to maximize cooling [2].](https://castman.co.kr/wp-content/uploads/image-114-png.webp)
6. Conclusions and Discussion:
This research presented a method for manufacturing high-performance heat sinks using high-vacuum rheocasting (Comptech process), achieving superior thermal conductivity and mechanical properties. The optimal alloy composition (low Si, appropriate Mg) and heat treatment enabled the attainment of thermal conductivity exceeding 180 W/mK at 100°C and yield strength surpassing 80 MPa. These heat sinks can incorporate complex designs with thin fins and are producible using 100% recycled aluminum. This study offers significant implications for heat sink design and manufacturing, particularly in applications demanding high performance. However, close collaboration between designers and casting experts is crucial for optimizing design, gating, and the overall process to achieve optimal results given the influence of process variables such as gate location and heat treatment on the final product.
7. Suggestions for Future Research:
This study focused on specific alloy compositions and processing parameters. Further research should investigate a broader range of alloy compositions and process variables. Long-term durability and reliability testing under various operating conditions are necessary. Performance evaluation across different cooling mediums (air, liquid) should also be conducted. Finally, further research is needed to optimize heat sink design and manufacturing processes for diverse applications.
References:
- I. Belov, M. Payandeh, A. E. W. Jarfors, P. Leisner and M. Wessén, "Effect of fillets on heat transfer in a Rheocast aluminum heatsink," 2016 17th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), Montpellier, France, 2016, pp. 1-6, doi:10.1109/EuroSimE.2016.7463320.
- A. Lafors, J. Zheng, L. Chen, J. Yang, Recent advances in Commercial Applications of the Rheometal Process in China and Europe M. Hartlieb, P. Jansson, S. Zetterström, High Vacuum Rheocasting for the Production of Large, Ultra-Thin-Walled Telecom Castings with High Thermal Conductivity, NADCA Transactions 2021.
- M. Payandeh, I. Belov, A.E.W. Jarfors, and M. Wessen, “Effect of Material Inhomogeneity on Thermal Performance of a Rheocast Aluminum Heatsink for Electronics Cooling,” Journal of Materials Engineering and Performance, Volume 25, Number 5, 2016, ISSN 1059-9495
- P. Olafsson, R. Sandstrom, Å. Karlsson, Comparison of experimental, calculated and observed values for electrical and thermal conductivity of aluminum alloys, Journal of materials science, 32 (1997) 4383-4390.2.
Copyright and References:
This summary is based on the research paper "Vacuum Rheocasting Heat Sinks with Significantly Improved Performance" by M. Hartlieb et al.
This summary is for informational purposes only and should not be used for commercial purposes without permission from the authors and the NADCA.
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