Preparation, Microstructure And Mechanical Properties Of Al Foam And Al Foam Sandwich Panels

ABSTRACT:Al foam as a new kind of structure and function material, has the structure characteristic and the performance advantages of the porous and metal materials. Due to the excellent properties such as low density, lightweight, sound-absorbing, energy-absorbing, it can be considered as a potential material for defence, transportation, aerospace applications. However, so far, there is no report regarding to the industrial production of Al foam in China owing to the production technology. At present, melt foaming process is the most suitable way to prepare of Al foam in industrial production. Since the high melting point of Al (660℃), the TiH2would decompose easily during preparation process, leading to the uneven structure of Al foam.Firstly, the influences of chemical plating coating on the properties of TiH2powders were investigated in this study. And then, the effects of the TiH2addition on the properties of Al foam such as the porosity, the compression performance and the damping performance were also evaluated. Besides, Al foam sandwich panels were manufactured by brazing method with Al-Si based alloy used as filler metal, Al foam used as matrix and pure Al or steel plates used as panels. The microstructure of the soldered interfacial region and the elemental concentration profile were determined by SEM and EDS, respectively. The diffusion of Si and Al were investigated by diffusion theory. In addition, the shear strength of soldered joints were also performed. The main results are obtained as following:(1) The chemical plating on the TiH2powders led to an increase in the starting temperature of releasing H2from450℃to540℃;(2) With the content of foaming agent rising, the porosity of the Al foam increased, and the damping property firstly enhanced and then reduced. According to the characteristic of compression stress-strain curve of Al foam, the elastic deformation stage was from the beginning to approximately0.5%; Plastic deformation stage as a platform area was from0.5%to50～60%, which was the embodiment of the compression strength and the energy absorption process of Al foam; and the densification stage was determined to the final;(3) In Al foam sandwich panels (Al plates as panels), Si was stepped distributed in the solder layer; The welding layer was reinforced by solid solution of Al and Si; The optimal brazing process is that the welding temperature is630℃, welding time is10min, stress relief annealing temperature is400℃and annealing time is30min;(4) In Al foam sandwich panels (steel plates as panels), the microstructures of joints were changed with the welding time. When the welding time is5min, the solder would not be melt thoroughly and a part of joints are not attached closely, led to a low shear strength; When the welding time is10min, the formation of Al and Fe solution as well as Al/Fe intermetallic compound are observed in the joints. Owing to the well connected joints the shear strength is reached the highest value of6.26MPa; With further increasing the welding time, a large number of Al/Fe intermetallic compound are formed in the joints and thus reduced the performance of joints and decreased the shear strength.