How can multilayer structural parts avoid electrochemical corrosion or thermal expansion mismatch when laminating dissimilar metals?
Publish Time: 2025-08-28
In modern high-end manufacturing, multilayer structural parts are widely used in aerospace, energy equipment, rail transportation, and precision machinery due to their excellent overall performance. When metal materials with different functional or mechanical requirements are laminated, joining dissimilar metals becomes a crucial means of achieving structural optimization. However, differences in electrochemical activity and thermophysical properties between different metals also pose challenges to the long-term stability of the structure, with electrochemical corrosion and thermal expansion mismatch being the most prominent. If not properly addressed, these potential risks can lead to interlayer delamination, joint failure, and even structural damage.Electrochemical corrosion occurs due to the potential difference between dissimilar metals in an electrolyte environment. When two or more metals are in close contact and exposed to moisture, salt spray, or industrial atmosphere, the metal with the more negative potential becomes the anode, accelerating corrosion, while the metal with the more positive potential acts as the cathode, providing protection. This phenomenon is particularly pronounced in common dissimilar metal combinations such as aluminum and steel, and copper and titanium. To block corrosion pathways, isolating the dissimilar metals from direct contact is crucial. A common approach is to introduce insulating interfaces between layers, such as polymer films, ceramic coatings, or specialized anti-corrosion gaskets. These materials can withstand assembly stresses while effectively preventing electron migration. Surface treatments such as anodizing, plating, or spray-on anti-corrosion coatings can also form a protective barrier on the metal surface, reducing its activity in electrochemical reactions.In some applications where complete isolation is not possible, designers will minimize potential differences by matching materials. Preferring metals that are close in the electrochemical sequence for lamination can fundamentally reduce the driving force for corrosion. Furthermore, structural design should avoid closed gaps or areas of water accumulation to prevent long-term electrolyte retention. Drain holes, ventilation structures, or sloped surfaces can help keep joints dry and reduce the environmental conditions that can lead to corrosion.Thermal expansion mismatch is another hidden threat. Different metals expand and contract differently with temperature changes. When a structure experiences thermal cycling, such as engine start-stop, day-night temperature fluctuations, or seasonal changes, the different expansion coefficients of the metal layers cause relative displacement. If this differential stress cannot be relieved, it will accumulate at the interfaces or joints between layers, leading to warping, cracking, or loosening of the connectors. To mitigate this problem, the choice of interlayer connection method is crucial. While rigid connections such as full welds or high-strength bolts offer high load-bearing capacity, they also restrict free deformation and can easily lead to stress concentration. In contrast, flexible connections, sliding joints, or elastic pads can allow each layer to expand and contract independently to a certain extent, reducing mutual constraints.In terms of material layout, gradient matching can be achieved through intermediate transition layers. For example, an alloy or composite material with intermediate properties can be added between two metal layers with significantly different expansion coefficients to create a gradual transition in thermophysical properties and reduce peak interfacial stress. Furthermore, structural geometry can optimize stress distribution, such as by using corrugated, honeycomb, or segmented structures to increase local flexibility and absorb thermal deformation energy.Controlling prestress during the manufacturing process is equally important. During assembly or welding, prestressing or controlling the cooling rate can offset some of the residual stresses generated by thermal cycling. Subsequent heat treatment processes can also help to equalize internal stresses and improve structural stability.In summary, when laminating dissimilar metals in multilayer structural parts, a multi-dimensional approach, including material selection, interface engineering, connection design, and structural optimization, must be employed to systematically address the challenges of electrochemical corrosion and thermal expansion mismatch. This is not only an application of materials science but also a profound consideration of structural durability and reliability. Only by fully anticipating and addressing these potential risks at the initial design stage can the long-term stable operation of multilayer structures in complex service environments be ensured.
