Preparation methods and problems of aluminum foam sandwich panels

The preparation of aluminum foam sandwich panelsis divided into two categories as a whole. The first category is to prepare the aluminum foam first, and then connect the aluminum foam with the Metal panel in different ways, such as cemented connection, surface thermal spraying method, and welding connection. The second type is to prepare the prefabricated body of the aluminum foam sandwich panel, and then the prefabricated body is heated to make the core layer foam, and the foam is cooled after the completion of the foam that is the aluminum foam sandwich panel. Commonly used preparation methods include hot pressing - powder metallurgy foaming method, rolling - coating - foaming method, and so on.

1. Glued connection

Gluing refers to the method of making sandwich panels by bonding aluminum foam to metal panels with appropriate adhesives. The gluing process adopts the phySical connection to prepare the sandwich panel, and the method has the advantages of simple procedure and high production precision. However, due to the structural characteristics of the high porosity ofaluminum foam, the removal of impurities in the holes on the surface of the aluminum foam is relatively heavy; in this connection method, the panel and the core layer are mainly glued at the aperture prongs, and the actual effective bonding area is small, which results in a low bonding strength of the sandwich structure; the adhesive fails at high temperatures or in strong corrosive environments, which causes the separation of the core layer from the panel and the destruction of the structure.

2. Welding connection

Welding methods for the preparation of foam aluminum sandwich panels include laser beam welding, ultrasonic torsion welding, and brazing connections. Laser beam welding is the use of a laser's high thermal energy to panel materials and foam aluminum surface layer melting, cooling after the two composite together, spot welding position, and welding sequence shown in Figure 1. Laser beam welding is highly accurate and can effectively control the melted joint area. Although this method can carry out continuous operation, the efficiency is low, and the product bond strength is also low. The principle of ultrasonic torsion welding is to join two materials together by ultrasonic energy. However, this method requires a certain welding area, and it is not possible to complete the welding of all target surfaces, which limits the use of this method in actual production. The brazing connection will be hindered by the oxidized layer of foam aluminum, so it is critical to remove the oxidized layer, and when applying brazing technology without brazing flux in foam aluminum sandwich panels, some anti-corrosion measures should be taken into account to prevent zinc-based and other alloys from combining with aluminum corrosion. In addition, the parts connected by this method only have hole prongs, so the bond strength will be reduced.

3. Surface thermal spraying method

The coating process generally requires a high degree of flatness on the surface of the component, so the method is not suitable for more complex structures. Thermal spraying belongs to a surface technology, which is realized by melting wires or powders. This method utilizes a jet of air to accelerate the melted material and transfer it to the surface of the component to be coated, enabling the processing of components with complex shapes. In this method, the heat source is generally an electric arc. However, this method is difficult to industrialize due to the complexity of the process.

4. Hot pressing - powder metallurgy foaming method

In this method, the core layer powder used for foaming is firstly placed in the panel, and then they are put into the mold together, and a hydraulic press is used to apply cold pressure to them, after which the blanks are held at 450 ℃ for about 1 h and then hot pressed to obtain the prefabricated blanks which can be operated for foaming. The preform is then heated and foamed in a closed mold, and the sandwich panel is obtained after cooling. The presence of the mold in this method will have some limitations on the size of the finished aluminum foam sandwich panel.

5. Rolling-coating-foaming method

This method is the original powder for foaming using appropriate rolling means to make the core material, after the panel and the prefabricated core material for rolling, coating, to obtain the pre-fabricated blanks, foaming after cooling to get a good structure of the sandwich panel. This method of preparation of products with high bonding strength can realize continuous production but needs to overcome two technical difficulties: one is the need to densify the powder, and the second is the effective combination of core material and panel rolling.