Metal composite panels, as a multi-layered structural material formed by metallurgically bonding different metals, often face the risk of interlayer delamination during the forming and processing process. This delamination typically stems from insufficient interfacial bonding strength, processing stress concentration, or differences in material properties. Therefore, targeted measures must be taken from multiple dimensions, including process design, parameter control, and equipment optimization.
In the rolling composite process, the bonding quality between metal layers is directly affected by the rolling force and deformation. Insufficient rolling force leads to inadequate interfacial contact, easily resulting in incomplete welds or porosity; while excessive rolling force may cause excessive formation of brittle intermetallic compounds, reducing bonding strength. Therefore, rolling parameters need to be adjusted according to the characteristics of the composite material. For example, asynchronous rolling technology can be used, creating a "rolling zone" through the difference in linear speed between the upper and lower rolls. This utilizes interfacial friction to generate heat, promoting metal atom diffusion and simultaneously breaking down the surface oxide film, enhancing the contact and bonding of fresh metal. Furthermore, multi-pass rolling with small deformation amounts can gradually release processing stress, avoiding interlayer tearing caused by a single large deformation.
Heat treatment is a crucial step in improving the interlayer bonding stability of metal composite panels. After hot or cold rolling, annealing can eliminate work hardening, promote interfacial atomic diffusion, and form a denser metallurgical bond. The annealing temperature needs precise control: too low a temperature results in insufficient atomic diffusion and limited improvement in bond strength; too high a temperature may trigger excessive interfacial reaction, generating a brittle phase. For example, during annealing of titanium-steel composite plates, excessive diffusion of titanium and iron must be avoided to prevent the formation of a hard and brittle FeTi phase. Rapid heating and short-time holding processes are typically used to reduce element diffusion time. Simultaneously, controlling the annealing atmosphere is crucial; vacuum or inert gas protection can prevent interfacial oxidation and ensure bonding quality.
Stress management during processing is another key aspect in preventing interlayer delamination. In forming processes such as bending and punching, uneven deformation between metal layers can easily lead to localized stress concentration. For example, during wide-edge bending, if the bending radius is too small, the outer metal layer will be overstretched while the inner metal layer will be undercompressed, potentially causing copper layer splitting or wrinkling. Therefore, a reasonable bending radius must be designed based on material properties, and side-bending dies or segmented bending processes should be used to balance the deformation of each metal layer. During punching, the clearance between the punch and die must be strictly matched to prevent separation of the copper layer from the aluminum core due to excessive clearance. Simultaneously, the punching position should be far from the end face to prevent interlayer cracking caused by edge stress.
Material selection and pretreatment have a fundamental impact on the quality of interlayer bonding. The mechanical properties and coefficients of thermal expansion of the base and cladding metals should be matched as closely as possible to minimize deformation differences during processing. For example, in aluminum-steel composite plates, aluminum's coefficient of thermal expansion is much higher than that of steel, easily generating thermal stress during heating or cooling, leading to interlayer separation. Therefore, it is necessary to alleviate thermal stress by adding a transition layer or adjusting the composite ratio. Furthermore, impurities such as oil and oxide films on the metal surface can hinder metallurgical bonding, requiring strict surface treatment before processing, such as mechanical grinding, chemical cleaning, or electrolytic etching, to ensure interface cleanliness.
Equipment precision and process stability are also important factors in preventing interlayer separation. Roll gap control, tension adjustment, and other parameters of the rolling mill must be precisely calibrated to avoid uneven rolling force caused by equipment vibration or parameter fluctuations, which can lead to interlayer slippage. In continuous composite molding, such as horizontal composite molding, it is crucial to ensure the synchronous feeding of the foam plastic raw material and the metal facing material to prevent poor local bonding due to uneven material distribution. Simultaneously, the movement speed of the mixing head and the coordination of the pressure rollers must be consistent to avoid excessive accumulation of reactants at the edges of the sheet, which would affect the quality of interlayer bonding.
For specific applications, the anti-separation capability of metal composite panels can be improved through structural optimization. For example, in components that need to withstand alternating loads, a gradient composite structure can be used to gradually transition the material properties at the interface, reducing stress concentration; or the mechanical interlocking force at the interface can be improved through fiber reinforcement and particle filling. Furthermore, during welding, appropriate welding methods and process parameters must be selected to prevent interlayer melting or embrittlement due to excessive heat input. For example, inert gas protection should be used when welding titanium-steel composite panels to prevent titanium layer oxidation, while controlling the welding heat input to reduce the width of the heat-affected zone.
Preventing interlayer separation of metal composite panels during molding requires a comprehensive approach, including process optimization, parameter control, material pretreatment, and equipment upgrades. By precisely controlling the rolling force and deformation, optimizing the heat treatment process, managing processing stress, strictly controlling surface treatment, improving equipment precision, and innovating structural design, the interlayer bonding quality of metal composite panels can be significantly improved, meeting their stringent application requirements in the petroleum, chemical, shipbuilding, and power industries.
