The matching of thermal expansion coefficients (TECs) in metal composite panels at high temperatures is a core challenge for their application as functional materials in aerospace, power electronics, and chemical equipment. Since composite panels are formed by metallurgically bonding two or more metals, differences in the TECs of different components can lead to interfacial stress concentration at high temperatures, causing interlayer delamination, warping, and even structural failure. Therefore, ensuring TEC matching requires a multi-dimensional approach encompassing material design, process control, structural optimization, and performance testing.
During the material design phase, the principle of "complementary performance" must be followed, selecting components with similar or gradient TECs. For example, in aluminum-based composite panels, aluminum has a high TEC; if combined with ceramics or high-carbon steel, the overall expansion behavior needs to be adjusted by adding low-expansion phases (such as silicon carbide particles). Similarly, stainless steel composite panels often use a base layer of carbon steel for strength and a cladding layer of stainless steel for corrosion resistance, but the cladding thickness must be controlled to balance thermal stress. For extreme high-temperature scenarios, metal-ceramic composites or particle-reinforced metal matrix composites (MMCs) are preferred, as they reduce the overall coefficient of thermal expansion through the constraint of the ceramic phase while maintaining the toughness of the metal.
Process control is crucial for ensuring compatibility, especially during rolling composite processes where synergistic deformation of the component materials is required. Hot rolling softens the metal at high temperatures, reducing deformation resistance and allowing the components to interdiffusion under pressure to form a metallurgical bond. However, strict control of rolling temperature and speed is necessary to avoid reduced bond strength due to oxide films or interface contamination. Cold rolling relies on large reductions to achieve atomic-level bonding, but subsequent diffusion annealing is required to eliminate work hardening. Asynchronous rolling technology introduces a "rolling zone" through the speed difference between the upper and lower rolls, promoting the exposure of fresh metal at the interface, enhancing bond strength, and reducing average rolling pressure and residual stress.
At the structural optimization level, transition layer design is an effective means of mitigating thermal expansion mismatch. For example, inserting functionally graded materials (FGMs) at the metal-ceramic interface allows for a smooth transition of the coefficient of thermal expansion through compositional gradients, avoiding abrupt stress changes. For multilayer composite panels, a symmetrical stacking structure can balance thermal stress in all directions, reducing the risk of warping. Furthermore, reserving expansion gaps or designing elastic buffer layers, such as adding flexible metal foil or polymer interlayers, can absorb some thermal strain and improve structural stability.
Simulation analysis provides theoretical support for thermal expansion matching design. Finite element analysis (FEA) simulates the stress distribution of composite panels under high-temperature conditions, predicting potential failure areas and optimizing material combinations and structural parameters. For example, for aluminum/steel composite panels, simulation results show that when the aluminum layer thickness exceeds 60%, the interfacial stress increases significantly under thermal cycling, requiring adjustments to the layer thickness ratio or the introduction of a low-expansion interlayer to improve performance. Such simulation results provide clear direction for experimental verification, shortening the R&D cycle.
Experimental testing is the final step in verifying matching. Thermal cycling tests simulate temperature fluctuations under actual operating conditions to evaluate the interlayer bonding strength and dimensional stability of the composite panel. Thermomechanical analysis (TMA) can directly measure the coefficient of thermal expansion of the material, ensuring it meets design requirements. Shear and tensile tests verify the mechanical properties of the composite panel in the directions perpendicular to and parallel to the interface, respectively, and determine the impact of thermal stress on the bond strength. For critical applications, long-term high-temperature aging tests are also required to observe the microstructural evolution of the composite panel, such as interface diffusion and phase transitions, providing a basis for reliability assessment.
Ensuring the matching of the thermal expansion coefficients of metal composite panels is a systematic project that needs to be implemented throughout the entire process of material design, process preparation, structural optimization, and performance testing. Through scientific material selection, precise control of process parameters, rational structural design, and rigorous verification, the adaptability of composite panels in high-temperature environments can be significantly improved, expanding their application potential in high-end equipment manufacturing. In the future, with the rapid development of wide-bandgap semiconductors, nuclear energy equipment, and other fields, the high-temperature performance requirements for metal composite panels will become more stringent, making the research and development of new low-expansion, high-thermal-conductivity composite materials an important direction.
