How is the aluminum foam connected to the material?

Bonding is a phySical connection method in whichaluminum foam and panelsare joined. It's a simple process that yields high-precision products. However, the surface cleaning of aluminum Foam and panels before bonding is relatively complex. Adhesives also have poor high-temperature and corrosion resistance, and the bonding strength is relatively low, which has limited the development of this method. Compared to bonding, welding significantly improves interface bonding strength. Currently, brazing and laser welding are the subjects of extensive research.

Brazing Method

Brazing is a widely studied welding method for aluminum foam sandwich materials. The key to this method lies in selecting the appropriate brazing material and removing the oxide film from the surface of the aluminum foam. Due to the electrode potential difference between the brazing joint and the aluminum foam base material, electrochemical corrosion can easily occur, leading to poor heat resistance and low joint strength. Wang Hui et al. used nitrogen protection to improve the stability of brazed joints. Their research indicated that no continuous film formed at the interface; instead, it consisted of contact points at the edges of the end pores. When using Zn-Al-Cu alloy as the brazing material, the welding process itself offers some de-filming functionality, avoiding corrosion issues caused by mechanical scraping. The use of a laying technique combined with ultrasonic vibration during welding ensures that the brazing material uniformly fills the pores, ultimately creating a metallurgical sandwich panel between the brazing material and the aluminum plate, and the brazing material and the aluminum foam. Chen Nannan et al. used a copper foil-aluminum sheet-copper foil composite layer as an interlayer and optimized the welding temperature to uniformly fill the pores, ultimately producing a metallurgical sandwich panel from the brazing material and aluminum plate and the brazing material and aluminum foam. Song Yufeng used an Al-Si-based alloy as the brazing material and pure aluminum plates as the panels. They brazed aluminum foam sandwich panels and employed an orthogonal experiment to examine the effects of welding temperature, time, and annealing process on the sandwich panel's performance. The optimal process parameters were: a welding temperature of 640∘C, a time of 15 min, and stress annealing at 400∘C for 30 min. Furthermore, a comparison of failures in samples brazed at 400∘C and bonded samples showed that the brazing method exhibited better stability at high temperatures than the bonding method.

Laser Welding Method

Laser welding is a method that involves radiating a high-intensity, high-energy laser beam onto a metal surface, melting it, and then joining the pieces together. The advantages of this method include minimal workpiece deformation after welding, high production efficiency, and the ability to achieve continuous production. Zhang Di et al. added 6061 aluminum alloy between aluminum foam (with 70% porosity) and the panel. They used the heat from a laser beam to melt the 6061 aluminum alloy, allowing it to penetrate the pores of the aluminum foam, thereby achieving better welding. The tensile strength of the welded joint was 2.97 MPa, close to the strength of the aluminum foam itself. However, during laser welding, the absorption of laser energy by the aluminum foam base material is limited due to reflection from the pore walls and the confined pore space within the aluminum foam. Under the action of a high-temperature heat source, the internal pores of the aluminum foam may collapse due to heat absorption and melting, forming a dense, wide weld zone. Laser welding is still in its early exploratory stages and has a long research path ahead before it can be used for industrial production.